Fast idle - PeachParts Mercedes-Benz Forum

bowman · #1 03-04-2009, 05:34 PM

I recently had a transmission problem where the governor had to be cleaned so that the car would upshift out of 2nd. However when I left the shop, the car now idles very high in park c. 2500 rpms and of course clunks when I put it in gear. It idles high in drive as well although not so high comparatively.

I have put in a new OVP relay on the car to cure a cold starting issue and that solved it but that was before the transmission issue.

I have read that I should clean the idle control valve because I have noticed that if I take off the air filter housing, and manually pull up on the valve that is right below the air filter, (sorry don't know the name) the idle goes back to normal, obviously because of the limited air flow, so I think the computer compensates for it and drops the idle accordingly.

Where is the ICV and any other suggestions? The fuel pump buzzes very loudly by the way and I have a replacement in the basement waiting to go on. Any ideas? Is the transmission problem related? Could the fuel pump affect the idle?

Thanks for the help.

bowman · #2 03-04-2009, 06:43 PM

Funnily enough the idle speed righted itself after fully warming up the car, but I'm not convinced that the issue will not return. Still any preventative steps to take? Anyone?

Arthur Dalton · #3 03-04-2009, 09:12 PM

If the condition returns, observe if the ABS lamp comes on at the same time.

bowman · #4 03-05-2009, 12:30 AM

No ABS light thus far. But when idle did calm down, I was running it with the air filter housing et al removed.

Arthur Dalton · #5 03-05-2009, 12:36 AM

I only mention ABS b/c if the OVP is acting up with an intermittant power feed , you will get the high idle and the ABS lamp will be the tip off of OVP failure b/c that same feed goes to the ABS module...so, if those two conditions are coupled , OVP or OVP fuse are suspect.

You can give it a few taps and see if the idle jumps too...

bowman · #6 03-05-2009, 10:28 PM

the problem came back this morning, so as untechnical as it sounds, the car did not fix itself after getting it's transmission governor serviced. It has just developed another symptom. It's Murphy's Law. Transmission sticks in 2nd and then a high idle. I am going to clean the ICV and see how it goes. This is becoming a challenging car.

bowman · #7 03-09-2009, 01:02 PM

I clean the Intake Control Valve and put it back on but the car still idles high. Of course I just unplugged the connector of the ICV and it drops the idle so until I can hook it up to a code reader I will just drive it with the ICV unplugged. It's 75 degrees here in NC so until it gets cold again it shouldn't be a problem.

rocky raccoon · #8 03-09-2009, 02:02 PM

Since the problem manifested itself after transmission service, I would logically look for a vacuum problem caused by that service. Did they forget to replace your vacuum modulator hose?

wildspine · #9 03-11-2009, 12:08 AM

Arthur- what is the OVP? My 88 420 has this problem occasionally where it idles high when the abs light is on only. Is is a difficult fix? Could an OVP malfunction cause the alarm system to malfunction as well (car alarms even if system is disabled by unlocking door with ignition key.)

Arthur Dalton · #10 03-11-2009, 11:07 AM

http://catalog.peachparts.com/ShopByVehicle.epc?q=1988-Mercedes--benz-4--0sel-Body--Electrical&yearid=1988%40%401988&makeid=63%40%40MERCEDES%2DBENZ%40%4063%40%40MERCEDES%2DBENZ%40%40X&modelid=6264%3AMBC%7C1533%3AED%7C10000055%40%40420SEL&catid=241959%40%40Body+Electrical&subcatid=242003@@Overload+Relay&mode=PA

Easy fix..just plugs in.

Use the search feature on top of the page .. "OVP"