MB-Wrencher

Hello all. I have a 1995 s600 that has a strange throttle issue. When I start the engine the idle will hang above 1000 for about 15 seconds, after that it will slowly start to come down to idle speed over the next 15 seconds. if I touch the throttle pedal at all within that 30 second span after starting, the RPM will go up to about 1900 rpm for a few seconds and then will surge between 1400 to 1600 and will keep doing that until I cycle the key. If I start the engine and let it come down to idle for 30 seconds and touch the throttle pedal it will rev and return to idle normally. There are no fault codes in any of the engine related control units. I have watched the actual values in all the control units when it does the surging and the only abnormal thing I see is the on-off ratio will go between 50% and 95%. Both throttle bodies and wiring harnesses are ok. The injector and MAF harnesses are good as well. Any help would be greatly appreciated!! Thanks!!

chassis

Unmetered air. Check the induction system carefully for leaks, for example cracked or loose plastic ducts, loose clamps or leaking intake gaskets.


Read codes and report them here.

MB-Wrencher

I checked for vacuum leaks and didn’t find anything. Did discover that this issue correlates with the secondary air injection being activated after starting the engine. If I touch the throttle while the secondary air is active it will have a surging fit. If I wait until the secondary air deactivates it will rev and idle normally.

MB-Wrencher

Turns out it is a faulty EGAS control unit!!!

MB_Fahrer

Glad you figured it out. Stuff like this is hard to solve online. Most people just say it's vacuum leaks. Which is right...some of the time. I can't tell you how many hours I've wasted fogging perfectly good vacuum and intake systems.