Nobody wants to reply in tech help!>>slight increase in idle - PeachParts Mercedes-Benz Forum

BenzOnline · #1 06-18-2003, 07:43 AM

Recently on my 126 the idle has increased by maybe 50-100 rpm (bareley noiticable on the tach) but enough to make the gears jump harder while changing from R to D etc. Sometimes when I have AC running then shut it off the idle is not the same but gets back to normal quickly but now its been 2 days. It happened pretty much overnight cause in the morning it was like that and still is now.

It is not the idle modulator (black box) cause when I had that go last yr it was all the way up to 1800 rpm.

Where should I look? Again its a slight increase but not too noticeable on the tach....though its noticeable while at standstill in D at a light.

thanks

rickg · #2 06-18-2003, 10:21 AM

Just a thought. Might check around for a vacuum leak. A hose that has cracked, or come loose, or something like that. That can effect the idle speed on any gas engine.
Best of luck!

BenzOnline · #3 06-18-2003, 11:17 AM

where do I start looking?

rickg · #4 06-18-2003, 11:34 AM

That's the $64,000 question. I don't know what your car looks like under the hood, but that's where. Lift the hood and start checking that rats-nest of vacuum hoses connected to the the intake manifold. Then work your way out from there. One thing I've done is get a can of good ol WD-40 and give a spurt at all the hose connections and suspicous looking hoses. If the idle speed makes a momentary change, you have at least one of the culprits. This can be either a real fast fix, or a long running nightmare, depending on the complexity of your system.
One thing to bear in mind on these W126's is the vacuum system runs all your heat/air vents. So might try tracing down the main hose to that and temporarily disconnect it and plug it off. Then start the car and see if anything improves. That hose should be either identified on a repair CD if you have one, or do a search on the forum. I know this has been discussed alot.

BenzOnline · #5 06-18-2003, 02:05 PM

this car is like a hoover!

BenzOnline · #6 06-18-2003, 05:11 PM

but is this for sure the problem? I have to check with my father who was the PO and see if he ever replaced the hoses. The slightly higher idle still continued today....slightly enough higher to make it more rough for shifting the gears (R,D).

How could this just happen overnight? Could it be the AC messed up something?

rickg · #7 06-18-2003, 05:18 PM

No, absolutely not a for sure thing. Could be several other things, which someone more familiar with your car would need to help you with, such as an injection system problem.
But vacuum leaks are a rather common ailment. So it's one of the first things I check for. They can kind of happen overnight, but usually will come on slow as a hose or fitting drys out and cracks. But it may not make a noticable difference until it reaches a certain point. Who knows, maybe you hit a bump in the road hard enough to jar something. Or you checked the oil and nudged a hose just right. Ect, ect.

BenzOnline · #8 06-19-2003, 10:32 PM

OK just got back from a 100km trip and on the way back a block from my home I stopped at a light and the RPM was where it should be (like 500-550 at idle in D) then turned the corner stopped at a stop sign and it was up slightly again like it was for the past few days then pulled into the garage and it was normal again! What gives? I have a feeling this problem will go away on its own....thats the thing about my car....you leave it and it eventually in a few weeks or days goes away.