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1997 SLK230K
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Discussion Starter · #1 ·
Hi Everyone

I have been experiencing a problem with my 1997 SLK 230Kompressor R170. This is the first generation, pre-facelift.

It all started when the engine suddenly cut off at a traffic light one day. I tried starting it but the engine would not fire up. It turned over easily as it normally does but after about few seconds the starter would disengage. I tried this for about 10 minutes in the middle of a busy intersection but the engine would not start. After calling for a tow truck I tried once again after a couple of minutes and to my surprise the engine fired up. The car ran fine after that for a few days but did the same thing again with increasing frequency.

It has since developed a misfire upon acceleration and an uneven idle. These symptoms are not consistent, because the idle returns to normal for short infrequent periods.

It has stalled on many occasions since then and when this happens it does not start up again right away. It only starts after many tries (more than 10 tries). Sometimes it only starts up again after it has been left to rest for about half an hour. I have not used the car for about 2 months because it is bound to stall in traffic.

I tried using the iCarSoft MB V2.0 fault finder but no faults show up. It's as though the iCarSoft MB V2.0 is not compatible with the R170. I didn't get much help from the iCarSoft customer care division. Its a useless piece of equipment.

After reading the many posts on this Forum that discussed the symptoms my car was displaying, I replaced the following parts, in the following order, with original Mercedes-Benz parts, without success.

  1. Replaced the K40 relay. No success.
  2. Replaced Fuel pump and fuel filter. No success.
  3. Replaced Fuel Pressure Regulator. No success.
  4. Replaced Crankshaft Position Sensor. No success.
Has anyone observed similar symptoms and how did you correct it?
Does anyone have any thoughts?
I would appreciate you sharing your thoughts.

Thanks
 

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2002 SLK320
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1,086 Posts
My first suggestion would be to look for a decent independent Mercedes specialist who has SDS for a decent scan as you've already thrown a few parts at it. But you would still have to get the car there and it depends how far away it is.

Carsoft is OK(ish) as far as it goes, but it's not much use on the pre-facelift models like yours as they aren't OBD compliant.

If you want to try more parts I would suggest the camshaft position sensor as "Sometimes it only starts up again after it has been left to rest for about half an hour" - ie cooled down a bit - is typical of some faulty sensors. The symptoms sound like my faulty crankshaft position sensor, but you've already replaced that. As you don't seem to be in a big hurry to fix it, I would wait for suggestions from other folk too.
 

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1997 SLK230K
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53 Posts
Discussion Starter · #3 ·
My first suggestion would be to look for a decent independent Mercedes specialist who has SDS for a decent scan as you've already thrown a few parts at it. But you would still have to get the car there and it depends how far away it is.

Carsoft is OK(ish) as far as it goes, but it's not much use on the pre-facelift models like yours as they aren't OBD compliant.

If you want to try more parts I would suggest the camshaft position sensor as "Sometimes it only starts up again after it has been left to rest for about half an hour" - ie cooled down a bit - is typical of some faulty sensors. The symptoms sound like my faulty crankshaft position sensor, but you've already replaced that. As you don't seem to be in a big hurry to fix it, I would wait for suggestions from other folk too.
Thanks for responding. Great suggestions. I was also thinking of going to an independent Mercedes specialist at this point. There are 2 that comes to mind in Brisbane. Im happy to be pointed in the right direction if you know of someone or had experience with a good independent MB specialist mechanic.

I am going to try a new camshaft position sensor tomorrow afternoon and will provide feedback then.

Thanks
 

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2003 SLK200
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43 Posts
Fwiw, I had a similar experience a few years ago on a Volvo I had which turned out to be the cam shaft sensor. As it was an auto I had to switch her from P to D to Reverse and back to P be able to start her up. That bit may have been a placebo of course.
 

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2003 SLK230
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217 Posts
I was guessing K40 , you've done that and more . May I suggest looking at your MAF sensor . No need to buy a new one atm , just check it for oil residue . These engines have an oversight where blow-by goes into the clean air passage, through the S/C, through the Intercooler , and through the MAF . Having read how fellow owners have had to remove all of those parts for a thorough cleaning , I would like it if you can cross that issue of the list .
 

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1997 SLK230K
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Discussion Starter · #6 ·
Fwiw, I had a similar experience a few years ago on a Volvo I had which turned out to be the cam shaft sensor. As it was an auto I had to switch her from P to D to Reverse and back to P be able to start her up. That bit may have been a placebo of course.
Thanks Abe, I’m going to change the cam sensor tomorrow. Fingers crossed.
 

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Discussion Starter · #7 ·
I was guessing K40 , you've done that and more . May I suggest looking at your MAF sensor . No need to buy a new one atm , just check it for oil residue . These engines have an oversight where blow-by goes into the clean air passage, through the S/C, through the Intercooler , and through the MAF . Having read how fellow owners have had to remove all of those parts for a thorough cleaning , I would like it if you can cross that issue of the list .
Thanks Elphie. One of the first things that I did was to clean the MAF sensor. There is definitely no oil residue in that area.

Just as background info: About a year ago there was a misfire so I replaced the Coil packs and the plug leads as well as the plugs. The car has done about 15,000km since then.

Thanks
 

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1999 SLK230K
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How does the car run with the MAF unplugged? It won't engage the supercharger but if it runs the same it rules that out. Cam shaft sensors can cause underload misfires so it is possible but also could be a fuel pump issue too. Try a camshaft sensor but a Bosch one, I always recommend when changing the sensors on these cars you should use Bosch or genuine many folks on here and in my own experience have had no success using cheap sensors and nearly always end up spending more money on a genuine or Bosch part. But only buy from a reputable parts supplier too. eBay and Amazon are often fake branded stuff not worth taking a gamble on, I know you might be thinking it's easy for you to say to spend as much as Bosch or OE sensors cost but it is honestly the least painful route. I like to save folks money if I can but when it comes to actually replacing sensors spend the money.

Also check for spark on all 4 plugs, you shouldn't use the old school methods of pulling the plug and resting it on the metal casing but to be honest it works and I e never done an damage to a coil doing it. The reason I say this is the coils quite often break down on these engines, the earlier pre Evo m111 uses two coil packs for 4 cylinders so 1 coil drives two spark plugs. That is a lot of work for any coil so when one coil goes down you lose two cylinders. Also this is more likely to happen when the engine is warm.

I by no means get it right every time so please only use these as a guide to help educate yourself a bit on these engines, I do occasionally get things wrong but I do these videos just to try give a visual explanation.


You may already know where the sensors are but this gives you an idea of what sensor can cause what issue.

Also check to see if your breather swirl pot is blocked, As elphie said these engines make a nasty habbit of killing MAF sensors and this is what causes it.


The video's may not help you any more than you already know but sometimes seeing is easier than reading.
 

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Discussion Starter · #9 ·
How does the car run with the MAF unplugged? It won't engage the supercharger but if it runs the same it rules that out. Cam shaft sensors can cause underload misfires so it is possible but also could be a fuel pump issue too. Try a camshaft sensor but a Bosch one, I always recommend when changing the sensors on these cars you should use Bosch or genuine many folks on here and in my own experience have had no success using cheap sensors and nearly always end up spending more money on a genuine or Bosch part. But only buy from a reputable parts supplier too. eBay and Amazon are often fake branded stuff not worth taking a gamble on, I know you might be thinking it's easy for you to say to spend as much as Bosch or OE sensors cost but it is honestly the least painful route. I like to save folks money if I can but when it comes to actually replacing sensors spend the money.

Also check for spark on all 4 plugs, you shouldn't use the old school methods of pulling the plug and resting it on the metal casing but to be honest it works and I e never done an damage to a coil doing it. The reason I say this is the coils quite often break down on these engines, the earlier pre Evo m111 uses two coil packs for 4 cylinders so 1 coil drives two spark plugs. That is a lot of work for any coil so when one coil goes down you lose two cylinders. Also this is more likely to happen when the engine is warm.

I by no means get it right every time so please only use these as a guide to help educate yourself a bit on these engines, I do occasionally get things wrong but I do these videos just to try give a visual explanation.


You may already know where the sensors are but this gives you an idea of what sensor can cause what issue.

Also check to see if your breather swirl pot is blocked, As elphie said these engines make a nasty habbit of killing MAF sensors and this is what causes it.


The video's may not help you any more than you already know but sometimes seeing is easier than reading.
Thanks Alex

Okay, so I disconnected the MAF as suggested and it still runs the same. That rules out any problems with the MAF.
I then replaced the Cam Angle sensor with a Honeywell brand (it was the only one I could get today. It cost AUD$140.) It is listed as genuine part for SsangYong and Mercedes M111 engine. Engine still runs rough.

I then confirmed that all plug leads were working by checking for a spark as you suggested. I then attempted to check for spark at all the plugs. I only managed to check numbers 1 and 3. These had good spark. But then I experienced a problem with the removal of the coil packs and think that I may have caused some damage
. The coils packs did not come off in one piece. Both coils packs came off without the lower connector and rubber insulation. Please see the attached pictures. Any advice on removal of the lower part that is attached to number and 2 and 4 plugs will be appreciated.

1. Coil Pack before removal
Gas Automotive exterior Auto part Metal Titanium


2. Lower part of coil pack still attached to plug
Audio equipment Font Gas Auto part Electronic component


3. I used a pair of pliers to pull the connector
Black Office equipment Auto part Gas Automotive wheel system


4. This is the result of pulling the connector
Gas Auto part Font Gun accessory Metal


5. Only the rubber insulation is still attached to the plug
Gas Automotive wheel system Auto part Automotive tire Electric blue



Any advice will be greatly appreciated.
Thanks
 

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*Premium Member
1999 SLK230K
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1,190 Posts
Thanks Alex

Okay, so I disconnected the MAF as suggested and it still runs the same. That rules out any problems with the MAF.
I then replaced the Cam Angle sensor with a Honeywell brand (it was the only one I could get today. It cost AUD$140.) It is listed as genuine part for SsangYong and Mercedes M111 engine. Engine still runs rough.

I then confirmed that all plug leads were working by checking for a spark as you suggested. I then attempted to check for spark at all the plugs. I only managed to check numbers 1 and 3. These had good spark. But then I experienced a problem with the removal of the coil packs and think that I may have caused some damage
. The coils packs did not come off in one piece. Both coils packs came off without the lower connector and rubber insulation. Please see the attached pictures. Any advice on removal of the lower part that is attached to number and 2 and 4 plugs will be appreciated.

1. Coil Pack before removal
View attachment 608684

2. Lower part of coil pack still attached to plug
View attachment 608685

3. I used a pair of pliers to pull the connector
View attachment 608686

4. This is the result of pulling the connector
View attachment 608687

5. Only the rubber insulation is still attached to the plug
View attachment 608688


Any advice will be greatly appreciated.
Thanks
Ive had this happen a few times on GM cars, spray some WD40 or any penetrating lubricant down the centre and around the outer of the rubber but try to leave the top end dry. Let it soak for a 10 mins then use some long nose pliers and very gently pull on it with the pliers not too hard though, keep working it and eventually the rubby boot will come free. The chances are it's water that sat in there and caused corrosion to grip onto the rubber boot.
 

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1997 SLK230K
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Discussion Starter · #11 ·
Ive had this happen a few times on GM cars, spray some WD40 or any penetrating lubricant down the centre and around the outer of the rubber but try to leave the top end dry. Let it soak for a 10 mins then use some long nose pliers and very gently pull on it with the pliers not too hard though, keep working it and eventually the rubby boot will come free. The chances are it's water that sat in there and caused corrosion to grip onto the rubber boot.
Got the rubber boots off eventually, with some WD40. Thanks for the advice.

Tested all spark plugs and all are firing.

Any other suggestions?

Thanks
 

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2003 SLK200
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43 Posts
Got the rubber boots off eventually, with some WD40. Thanks for the advice.

Tested all spark plugs and all are firing.

Any other suggestions?

Thanks
When the engine cuts out, can you recall if there were still lights on the dash or not? It could be the ignition switch at fault if it cuts out and there are no dash lights.
 

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1997 SLK230K
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Discussion Starter · #13 ·
When the engine cuts out, can you recall if there were still lights on the dash or not? It could be the ignition switch at fault if it cuts out and there are no dash lights.
I didn't take notice of the dash lights. But I will keep an eye out for that the next time the engine cuts out.

Thanks
 

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1999 SLK230K
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No worries glad it helped, without diagnostic tools SDS I tend to go with old school check list of air, fuel and spark. So we know you have spark, fuel is a bit more difficult to test and used more questionable methods. The next simple thing is check the throttle body operation, it's not uncommon for the throttle "pedal" position sensor in the engine bay to fail (this is quite an expensive part) when it does fail it does cause a misfire as the car tried to guess entirely what it's doing when it fails.

This video I show the simplest way to see if it's working, so if you can get the car to run even roughly it will give you an idea if the throttle body is moving within moderate relation to the throttle pedal position sensor.

It's by no means scientific or technical but it gives a good idea if it's working right. I always say to use my videos as a guide as I don't always get things right, but do try to help explain things the best I can.

When the car does run does the supercharger engage when the car does run?

Really issues like this do need some time on SDS to locate the issue, often works out cheaper than the diagnostic dartboard method.

Does the car sound like it's down more than 1 cylinder? Also how is your coolant level and does the coolant look clean?

With your car being a M111 pre Evo by the age our cars are now it's also not uncommon for a headgasket to go bad, this is the worst case scenario and for a competent mechanic isn't a very complex job due to how basic these engines are. But the standard Victor reinz headgaskets weren't the best to start with on the Evo engine I believe Mercedes went to a different headgasket which is why less Evo engines have this issue. Like I say it's the worst case scenario.

It could also be a vacuum leak the most likely culprit being the seal under the throttle body, the easiest but no t most accurate way to test this is. 1 get a can of aerosol brake cleaner from a parts store(make sure it's the flammable stuff), 2 start the engine (if you can keep it running) 3 spray the brake cleaner around the intake manifold side (Do Not get it near the air intake itself in the exhaust side). Commonly if there is a vacuum leak the revs will pick up when the brake cleaner is drawn in or you may just notice the engine tone change.

I know that's a fair bit to take in, I try to suggest the cheapest methods of testing first.
 

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Discussion Starter · #15 · (Edited by Moderator)
No worries glad it helped, without diagnostic tools SDS I tend to go with old school check list of air, fuel and spark. So we know you have spark, fuel is a bit more difficult to test and used more questionable methods. The next simple thing is check the throttle body operation, it's not uncommon for the throttle "pedal" position sensor in the engine bay to fail (this is quite an expensive part) when it does fail it does cause a misfire as the car tried to guess entirely what it's doing when it fails.

This video I show the simplest way to see if it's working, so if you can get the car to run even roughly it will give you an idea if the throttle body is moving within moderate relation to the throttle pedal position sensor.

It's by no means scientific or technical but it gives a good idea if it's working right. I always say to use my videos as a guide as I don't always get things right, but do try to help explain things the best I can.

When the car does run does the supercharger engage when the car does run?

Really issues like this do need some time on SDS to locate the issue, often works out cheaper than the diagnostic dartboard method.

Does the car sound like it's down more than 1 cylinder? Also how is your coolant level and does the coolant look clean?

With your car being a M111 pre Evo by the age our cars are now it's also not uncommon for a headgasket to go bad, this is the worst case scenario and for a competent mechanic isn't a very complex job due to how basic these engines are. But the standard Victor reinz headgaskets weren't the best to start with on the Evo engine I believe Mercedes went to a different headgasket which is why less Evo engines have this issue. Like I say it's the worst case scenario.

It could also be a vacuum leak the most likely culprit being the seal under the throttle body, the easiest but no t most accurate way to test this is. 1 get a can of aerosol brake cleaner from a parts store(make sure it's the flammable stuff), 2 start the engine (if you can keep it running) 3 spray the brake cleaner around the intake manifold side (Do Not get it near the air intake itself in the exhaust side). Commonly if there is a vacuum leak the revs will pick up when the brake cleaner is drawn in or you may just notice the engine tone change.

I know that's a fair bit to take in, I try to suggest the cheapest methods of testing first.
Thanks for the advice and tips on fault finding.

The supercharger does engage but does not stay engaged. It tends to stop working as the engine begins to run rough on acceleration.

The coolant is clean and is a nice blue colour. There is no water in the oil or oil in the water. So i don't think it is the head gasket.

I checked the throttle body and there was movement. However the movement appeared to be somewhat erratic and the flap did not open more than 30degrees from closed position.

I did the vacuum test with the brake cleaner but could not detect a leak.

At this point I decided to get the car to an independent mercedes specialist. However I thought that i should try one last thing and clean the throttle body flap to see if it improved the opening of the flap. I sprayed the brake cleaner on the hinge of the flap and also a little WD40 and physically tried to get the flap to open a little more. I don't think I did much to improve the functioning of the throttle body, or at least I did not observe any improvement in the way it functioned. So I put everything back and started the car and the misfire was gone.

This was 3 days ago. I did not want to report this earlier because I wanted to drive the car for a few days to see if the problem was really gone. I have done about 60km since then and it drives well. However I have not driven it hard for fear that the misfire will return. I plan on putting a new set of platinum plugs in the next few days. Hopefully the problem is fixed.

I am not sure what corrected the problem, but the last thing that I did was to clean the throttle body flap and try to get it to open smoothly and as much as possible.

So finally please advise me on the best way to service the throttle body.

Thanks
 

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1999 SLK230K
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1,190 Posts
I'm pleased to hear at least for that it's cured, I wonder if it my have been some carbon on the back side of the throttle butterfly preventing it from sitting in the position it should. Or the contacts on the plug could be dirty.

Normally the supercharger disengaging though is a sure fire sign that points to the MAF sensor failing to damaged wires. That or the bypass valve attached to the airbox, the throttle body and the bypass valve work together to limit the torque. Th bypass valve can also be something to keep and eye on, so for future reference.


As for the supercharger engagement:

When there is load on the engine the supercharger does engage sooner.

As for servicing the throttle body, the only real things you can do with the throttle body is remove the throttle body inspect the seal between the intake manifold and the throttle body. It'st's just an o-ring type seal that fits around a bowl shaped bit of mesh that sits in the intake manifold inlet. Then just do as you have give the throttle blade a good clean, make sure the contacts in the plug are clean too.

the seal between the throttle body and manifold should when seated still sit a little proud of the flange, if it doesn't it maybe worth replacing.

im sorry that isnt a great answer to your question on servicing the throttle body, but unless you have very good electrical and mechanical knowledge I wouldn't advise opening up the motor housing.

i hope the car keeps running good for you and thank you for updating us.👍
 
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