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1998 SLK230K
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13 Posts
Discussion Starter · #1 · (Edited)
I'm sure it's somewhere in this encyclopedia, but I couldn't find it through some searches, so I'll go ahead and ask a few questions.

1. Why does this car have 2 throttle bodies? (Found out it's for the supercharger, so could I just let that vent to atmosphere or would it throw a code?) There's the one on the airbox and the one on the intake, I wanted to fab an aftermarket intake for the supercharger noise, and was pretty confused having my eyes on the car for the first time.

2.are there any actual kits for the intake system that I could just buy, or is there a way I could work this second body into it.

3. Will replacing the radio cause theft system issues? I'm not very satisfied with the stock one, the sound that comes out is extremely bass heavy, and I'm gonna redo the entire sound system.

4. What are some of the most crucial things to check, and maintenance items at 84k miles that should be done. just got this car, it's for my gf, and I want it to be as reliable as possible.
 

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*Registered
2002 SLK32 (x1), 2003 SLK230 (x2)
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366 Posts
The two intake butterfly valves, one is supercharger bypass, and the second is the throttle .

Cold air intake is of minimal value, the intake resonator body can be removed to add supercharger whine, if that is what you want. Add an oil catch can while you are at it. But do this experiment last after everything else down this list is addressed, haha

Car won't care about radio substitutes. Beckerusa sells a plug in replacement that is branded continental or vdo, sounds nice, looks factory, and has all modern features. Speaker upgrades might be next step, but considerable work. Be prepared to reglue both interior door panels, as taking apart to replace speakers will probably break 20 year old glue seams and snap attachment points. Gorrila glue is your friend.

Crucial things - at 84k odds are there is deferred maintenance. Check records if available and address anything not done on schedule. Change all filters and fluids, coolant, trans, diff, brake, etc if not done within last 5-7 years.

Check ball joints, control arm bushings, motor and trans mounts. Lemforder is best oem brand of the suspension parts.

Check taillight brake light bulb sockets, should be blue. If not, replace to solve intermittent bulb problems. Use Mercedes brake bulbs to ensure proper wattage and brightness.

Replace seal in roof lock hydraulic cylinder (above headliner) if not already done. Odds are this seal will go bad if not already and ruin a $400 discontinued headliner. Open roof halfway while engine is running and remove 3 screws in front edge of headliner, pull down and peek at cylinder to see if leaking. Check hydraulic fluid level of roof in rear quarter panel to see if on full mark...if low, don't just add..find the leak.

Check all drivetrain for leaks. Check shocks for leaks, stick with genuine MB parts or Bilstein B4 if replacing to maintain a factory/balanced ride.

Track down any rattles or squeaks. Its worth the time to fix. Usually a matter of missing rubber bits or plastic snaps. The piano hinges on rear package shelf wings needed recrimping on 3 of 5 cars I had to stop the rattle.

Tinting mirrors work? Pricey replacements, but nice to have them working.

Stick with genuine Mercedes parts, no alternate or Chinese substitutes.
Hopefully your local dealer is pleasant to work with, they are not always more expensive. Partscontainer is a very good ebay seller of genuine parts.

Once sorted these are great cars, just don't take shortcuts on parts and maintenance

Happy top down spirited motoring, sorted.

R
 

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*Premium Member
1999 SLK230 Turbo
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2,313 Posts
Cheers @Avel Du

As stated above the throttle body on the airbox is a "supercharger bypass valve" and the one on the intake is the actual throttle body.

The supercharger bypass valve is something that unfortunately causes the most issues when trying to modify these cars, it cannot be permanently removed and is always venting some boost pressure. Many people have tried to find a way to remove it but I've tried most methods and always loose performance, the only way to get rid of it for a vacuum set up is to switch to a stand alone ECU.

However all is not lost and a cold air feed is a great way to improve performance as the standard intake system is extremely restricted and just opening it up give the car a lot more top end pulling power.

One thing to liven the car up as yours is a pre Evo M111 is to relocate the MAF sensor, this is something that Mercedes actually did on post 2001 this gives better more lively throttle response.

Then there's the airbox itself with the Slk it has a different design airbox to the clk but the same principle applies, however if a true cold air feed kit is available that can accommodate the standard S/c bypass valve go for that option as you will see an improvement. Some airboxes actually have a little removable pipe inside them if I remember right it restricts the actual intake to something crazy like 50mm which is way too small for a 2.3 na let alone supercharged.
 

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*Premium Member
1999 SLK230 Turbo
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2,313 Posts
Finally you can modify your air box but this may introduce warmer engine bay air into the intake. However I did it on the wing side of my air box and never saw any issues only gains, however there are some out there that would argue this is not the way to do this 😂 kind of true to be fair.
 

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*Registered
1998 SLK230K
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13 Posts
Discussion Starter · #7 ·
Thanks for all the info everyone I never responded before and I apologize for that. I'll post some updates on the slk later, it's been a great car that's fun to drive and my gf is absolutely in love with it and wants to do performance mods on it. This forum is an excellent resource that's helped me understand the INS and outs of a German car that's as old as I am.
 

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**Premium Member '02 R170 SLK V8 5.0 & '00 SLK320
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9,033 Posts
My V8 SLK has a 76mm D A V E dual cold air intake ....

Car Vehicle Hood Motor vehicle Automotive design


:D :D :D
 

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*Registered
1998 SLK230K
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13 Posts
Discussion Starter · #12 ·
Hood Motor vehicle Automotive tire Automotive design Automotive exterior


So I figured a way to do the intake, and got it in. Love the supercharger sound, and I'll properly build a box around it in the coming weeks. One problem I've ran I to though, and wonder if any of the more experienced members know a solution to this.

When highway driving, if you go to hold 75 mph or use cruise control, and go down a hill, it feels like you're stepping on the pedal and letting off 1-2 times a second. It's always on decel and usually only at higher speeds, but rpms sometimes wander while city driving too. I assume this has to do with the bypass valve no longer giving it's sair to the intake like the stock box, or if maybe the filter I have in the bypass is too restrictive, as it's a modified large pcv filter.

I've had it in for several days and it's driven fine except for that issue, and I'm installing an exhaust tomorrow, but when getting home from about 80-100 miles of driving, it threw a check engine light. I'll scan it tomorrow to see what it says, and post an update on it.
 

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1998 SLK230K
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13 Posts
Discussion Starter · #13 ·
Here's the update, codes were for fuel trim and something about a clutch but I'm pretty sure it's supposed to be the air bypass valve, reader has the wrong definition. Here's the codes.
Vehicle Bicycle handlebar Automotive tire Motor vehicle Sports equipment

Bicycle handlebar Vehicle Motor vehicle Communication Device Automotive tire


I believe my theory about the bypasses filter being too restrictive is correct, and it's not venting as fast as it thinks it should be, so it thinks the valve is out of range. I'll do some more testing when I can, maybe one of you guys can give me some breadcrumbs to follow.
 

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**Premium Member '02 R170 SLK V8 5.0 & '00 SLK320
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9,033 Posts
" Warning !! ....................... beep beep beep ................... Warning !! ..................... beep beep beep ...................

Warning !! ....................... OBD Readers are not what they appear ................... There may be more Codes in other systems ................... There may be more Codes in Engine ECU ................... OBD does not see All Codes, nor does it see all systems ........................ SDS is needed ........................ beep beep beep ....................... beep beep beep
" :ROFLMAO:

If you want to know more search the many threads I have typed about why a clone SDS is essential for accurate hassle free diagnosis on R170 Cars, all the others that don't cost way more than Clone SDS will just lead you up the garden path.
 

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1998 SLK230K
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13 Posts
Discussion Starter · #15 ·
" Warning !! ....................... beep beep beep ................... Warning !! ..................... beep beep beep ...................

Warning !! ....................... OBD Readers are not what they appear ................... There may be more Codes in other systems ................... There may be more Codes in Engine ECU ................... OBD does not see All Codes, nor does it see all systems ........................ SDS is needed ........................ beep beep beep ....................... beep beep beep
" :ROFLMAO:

If you want to know more search the many threads I have typed about why a clone SDS is essential for accurate hassle free diagnosis on R170 Cars, all the others that don't cost way more than Clone SDS will just lead you up the garden path.
I've been a mechanic for quite some time, I'm well aware that obd won't catch everything, I just grabbed one to see what the car was saying after making modifications to it.
 

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1998 SLK230K
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Discussion Starter · #16 ·
So I took the intake off the manifold side, and in the strainer under the throttle body was the cover on the side of the maf sensor. The cover blew off and the maf got moisture in it. New on ordered, should be good to go soon. I'll keep updating.
 

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1998 SLK230K
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13 Posts
Discussion Starter · #17 ·
So I took the intake off the manifold side, and in the strainer under the throttle body was the cover on the side of the maf sensor. The cover blew off and the maf got moisture in it. New on ordered, should be good to go soon. I'll keep updating.
Here's the codes before I took the intake off, I had been unplugging and replugging things to check for differences in performance but I'm putting these here for continuity sake.
Communication Device Gadget Finger Gas Font

Communication Device Gadget Finger Telephone Bicycle accessory
Gadget Communication Device Audio equipment Gas Font

Gadget Bicycle accessory Communication Device Bicycle part Font

Gadget Plant Communication Device Bicycle accessory Finger

Gadget Bicycle handlebar Plant Finger Audio equipment

Gadget Communication Device Bicycle accessory Audio equipment Gas
 

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*Registered
1998 SLK230K
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13 Posts
Discussion Starter · #18 ·
Here's the codes before I took the intake off, I had been unplugging and replugging things to check for differences in performance but I'm putting these here for continuity sake. View attachment 621508
View attachment 621509 View attachment 621513
View attachment 621512
View attachment 621511
View attachment 621510
View attachment 621507
This scanner is actually really good and has OEM enhanced setting that'll look deeper and get more specific. May not be as good as sds but it'll get the job done for me.
 
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