just cant fix the idle surge up and down - PeachParts Mercedes-Benz Forum

bdemir · #1 12-22-2002, 01:50 PM

replaced o2 sencor
replaced idle control valve

used premium gas and gas clearners.

when idle control vavle was replaced it was good till about two weeks later then i cleaned it out and that did not help.

What else can be done.

Some probems are hard to troubleshoot on these cars.

Bedros

suginami · #2 12-22-2002, 03:20 PM

I bet you have a vacuum leak.

It allows "false air" into the system and prevents the idle control valve to figure out the proper amount of air, thus causing the idle to hunt up and down.

bdemir · #3 12-22-2002, 04:30 PM

Ok where do i start looking for a vacuum leak?

suginami · #4 12-22-2002, 04:35 PM

You could have a vacuum hose that has become disconnected.

You could have vacuum hose(s) that are cracked.

You could have a bad seal at the intake manifold gasket. I had an idle that went up and down, and my leak was at the intake manifold seal.

Q · #5 12-22-2002, 09:49 PM

Describe your problem in more detail. It could be the idle speed control module. I have a nearly free fix for that one.

#6 12-23-2002, 10:25 AM

What is the free fix?

Twisting the board and checking the idle? I have narrowed the search on my 380 SE to the idle control computer, but even after I re soldered the connections, it did not fix it. The leak issue may exist, my idle is OK some of the time, then races up to 1500 other times. Its completely random, sometimes it races the it drops down to 200 rpm and car amost stalls for a moment, then it climbs again. Most of thwe time these days it is high (1500 rpm).

I have a 380 sl from which I should be able to borrow a computer, but cannot find it on the SL, I even pulled the underside of the dash and passenger side kickplate, but can't find it.

Cheers,

John

Q · #7 12-23-2002, 10:45 AM

Resoldering the board is what I was going to suggest.

aldedmon · #8 12-23-2002, 10:47 AM

Buy 2 cans of Brake cleaner(aerosol cans) spray it all around you engine area everywhere you see a vacuum line. All around the intake area. If / where there is a leak, the car will stall. I had a similiar/same thing happening on my 92 400E. After fixing all the leaks, the car began to idle very poor when first started in the AM or after work and them would occasionally surge as you describe at idle or during Stop n Go. I had my injectors "Purged" and that solved my problem(for full details see my post - 400E missing problem fixed). Run better, more power, strong acceleration and No MORE MISS/SURGE

#9 12-23-2002, 10:59 AM

How do I purge the injectors?

aldedmon · #10 12-23-2002, 11:22 AM

You may not be able to do it your self , but my neighbor tell me that your friendly neighborhood FORD dealer can do it for ~$120(I'm sure any MB or independent could do it for little more $#$#)

400E's miss Finally Fixed!!!!(Clogged Injectors)

I had my 93 500E and my 94 530iT BMW both purged yesterday.
In ALL cases, when the apparatus is connected the discharge side guage starts out very erratic. occilating +- 2 lbs. Gradually it become rock steady. The end result is just like that Texaco System 3 commercial. The side by side comparison showing one injector flowing at max capacity and the other with a strangled stream . Now all 3 of my cars are flowing at MAX capacity. Benefits: Increased performance, better fuel economy, better acceleration, and peace of mind. I'm gonna get them done annual/biannually now for sure.

#11 12-23-2002, 11:25 AM

I had a similar issue with a 1996 E320: idle surge and also a check engine light. fuel injectors were purged, O2 sensor replaced and the idle surge problem persisted. In due course, I replced a fresh set of Champion plugs (listed as approved in the owners manual) with Bosch plugs and the problem went away. It is possible that this resulted in reestablishing a faulty connection, but it made me a believer in Bosch plugs.

bdemir · #12 12-24-2002, 12:13 AM

Thank you for posting.
I will try replacing the plugs first and then try the brake fluid thing. Should i be listening for any sucking or hissing sounds coming from a vacuum leak.

Bedros

suginami · #13 12-24-2002, 12:39 AM

Quote:

Originally posted by bdemir
Thank you for posting.
I will try replacing the plugs first and then try the brake fluid thing. Should i be listening for any sucking or hissing sounds coming from a vacuum leak.
Bedros

Yes. You can also spray water at the vacuum hoses and the intake manifold gasket to see if it bubbles.

aldedmon · #14 12-24-2002, 09:44 AM