'98 SLK230 intermittant stumbling during acceleration - Mercedes Benz SLK Forum

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#1 Old 08-30-2013
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'98 SLK230 intermittant stumbling during acceleration

My wife's daily driver, has 73K miles. She called this morning and said it stumbled and lost power (slightly) during overtaking another car on the freeway. When she stopped at the next red light she noticed a very rough idle and a CEL.
She stopped shut the engine off and restarted it. It ran smooth so she drove it home.
I checked and only found code P0455 which has always been a loose gas cap in the past. No other codes.
I pulled the MAF and cleaned it although, there is no evidence of oil in the air tube. Also, I pulled the K40 relay and resoldered a couple of 'suspect' joints on the pcb. Although, I do not think that was the problem.

Test drive shows a slight hesitation under full throttle then it seems to clear up. Other times it runs great.
Idle is smooth but I can detect an intermittant miss above idle speed when holding it at around 1500 rpm.

I doubt it's plugs since it seems to clear itself up. I'm puzzled.
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#2 Old 08-31-2013
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Add new plugs to the list.

It runs a bit better but still doesn't seem to pull as hard as I remember under full throttle.
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#3 Old 08-31-2013
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Originally Posted by DSM126 View Post
Add new plugs to the list.

It runs a bit better but still doesn't seem to pull as hard as I remember under full throttle.
Maybe you have a vacuum leak somewhere?


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#4 Old 09-04-2013
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Quote:
Originally Posted by DSM126 View Post
My wife's daily driver, has 73K miles. She called this morning and said it stumbled and lost power (slightly) during overtaking another car on the freeway. When she stopped at the next red light she noticed a very rough idle and a CEL.
She stopped shut the engine off and restarted it. It ran smooth so she drove it home.
I checked and only found code P0455 which has always been a loose gas cap in the past. No other codes.
I pulled the MAF and cleaned it although, there is no evidence of oil in the air tube. Also, I pulled the K40 relay and resoldered a couple of 'suspect' joints on the pcb. Although, I do not think that was the problem.

Test drive shows a slight hesitation under full throttle then it seems to clear up. Other times it runs great.
Idle is smooth but I can detect an intermittant miss above idle speed when holding it at around 1500 rpm.

I doubt it's plugs since it seems to clear itself up. I'm puzzled.
My '99 was similar, I didn't get any codes. I tracked it down to a failing Crankshaft Position Sensor. It's located at the top rear of the engine, right near where the Transmission and Engine mount together. Once I replaced it, the car returned to normal.
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#5 Old 09-05-2013
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I hate just swapping parts but, the CPS seems cheap and easy enough. I may give that a shot.
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#6 Old 09-05-2013
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Originally Posted by DSM126 View Post
I hate just swapping parts but, the CPS seems cheap and easy enough. I may give that a shot.
I have an extra CPS, if you want it you can have it. I changed my CPS because my car was stalling but that wasn't the problem. So I have an extra one now.

BTW, its 13 years old and you need a special instrument to change it. You will be paying for shipping.
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#7 Old 09-06-2013
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Thanks for the offer T-storm. Although, the part is cheap enough new and who knows... you might need it in the future.

In the meantime I have a CEL on my E320 that I need to tend to. Funny, it's running fine but displays a CEL while the SLK runs like crap and shows no faults.

Reminds me why I like the old W126 300SD so much. She never lets me down.
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#8 Old 09-06-2013
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Quote:
Originally Posted by thunderstorm View Post
I have an extra CPS, if you want it you can have it. I changed my CPS because my car was stalling but that wasn't the problem. So I have an extra one now.

BTW, its 13 years old and you need a special instrument to change it. You will be paying for shipping.
special instrument? I just needed a external torx, not sure the size or if that's what it's called...I guess you could say it was "special"
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#9 Old 09-06-2013
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Quote:
Originally Posted by thunderstorm View Post
I have an extra CPS, if you want it you can have it. I changed my CPS because my car was stalling but that wasn't the problem. So I have an extra one now.

BTW, its 13 years old and you need a special instrument to change it. You will be paying for shipping.
Quote:
Originally Posted by FireMist99 View Post
special instrument? I just needed a external torx, not sure the size or if that's what it's called...I guess you could say it was "special"
I started to notice how many Exx nuts there are (and hence sockets needed) so I got myself a set. "30 PIECE STAR SOCKET DRIVER TORX BITS SOCKET SET" cost 12.50 GBP, inc p&p.

But I realise from my Renault that there are some places where the Torx bits can be exchanged with allen bits, so I would expect to be able to use a 6-side socket in place of a star socket.
I do try to use the right bit, but sometimes, on the far side of a manifold, when the first two bolts have been torx, I end up using a torx on the next (allen) bolt.

PS Slight overlap with the set above, but again 12.50 GBP inc p&p. "40 Piece Torx Star Spline Hex Socket Bit Set. 3/8 and 1/2 Drive". Thoroughly recommended.
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