Fluctuating engine RPM

[estrellajon]

Lately, when I stop at a light, the engine RPM seem to fluctuate for a couple seconds. The RPM would jump up to 1K and back down to normal 2-3 times before it settles back.

Has anyone experienced this? I'm not sure what the ECU detects and tries to compensate for it.

[jnenad16]

MAS. and please do a search before the moderators go hard at you for not searching.

nenad

[manny]

Originally posted by jnenad16
MAS. and please do a search before the moderators go hard at you for not searching.
nenad

He posted at 12.23 am.
The Moderators are either sleeping or out drinking. :D

[estrellajon]

Originally posted by jnenad16
MAS. and please do a search before the moderators go hard at you for not searching.

nenad

Yeah Ill do that. I tried seaching before posting but could not find the symptoms I was having. Besides, What good is this site if I can't bring up certain questions. How sure are you its the MAS? If all answers are on this site, might as well disable the new thread button and leave the search functionality.:confused:

[Ashkan's C280]

:werd:

[jnenad16]

i know what you are saying, but if everyone keeps asking the same question with the same symptoms, this site will get crowded with repeating threads and wont be popular for anyone anymore. the administrator and the moderators are trying everything to prevent that. also, the faulty MAS would give these symptoms, but you can never be 100% sure until you scan the ecu, regardless of CEL being off. people should get this done before posting a question on this or any other forum, and from there the forum members can assist you further.

nenad

[CKlasse]

Get a diagnostic done by your local dealer or independant MB shop. Just as Nenad said, that's a common symptom that the MAS is failing. Which MB do you have anyway? Most 4 cyl. engines' RPM usually fluctuate during idle.

:)

[jnolte]

Originally posted by estrellajon
Yeah Ill do that. I tried seaching before posting but could not find the symptoms I was having. Besides, What good is this site if I can't bring up certain questions. How sure are you its the MAS? If all answers are on this site, might as well disable the new thread button and leave the search functionality.:confused:




:rolleyes:

[kameraguy]

Sorry for the late reply.

But yeah, if you are sitting still and the idle is fluctuating, the MAS is most commonly at fault.

In my case I had a bad MAS (*cough* stoopid k&n *cough*), and it resolved the issue when at idle.

But when I came to a slow stop, say letting the car idle forward slowly, my RPM would bounce a lot too.

For my case, it ended up being of all things a tranny with low fluids. Found a small leak and the tranny was low. Once I got that corrected, my fluctuating idle at slow speeds/crawls were resolved.

[estrellajon]

Originally posted by kameraguy
Sorry for the late reply.

But yeah, if you are sitting still and the idle is fluctuating, the MAS is most commonly at fault.

In my case I had a bad MAS (*cough* stoopid k&n *cough*), and it resolved the issue when at idle.

But when I came to a slow stop, say letting the car idle forward slowly, my RPM would bounce a lot too.

For my case, it ended up being of all things a tranny with low fluids. Found a small leak and the tranny was low. Once I got that corrected, my fluctuating idle at slow speeds/crawls were resolved.

I replaced it last weekend and runs so much better. At least now I can concentrate on changing the handling a bit. I'm currently doing the research on this site reading previous posts.