I have a 1990 560 SEL that I'm trying to get a few bugs out of. I fixed the heat thanks to a tip on the monovalve. I had an annoying high speed vibration which I cured by cleaning the backs of the wheels and rebalancing them. One problem I still haven't fix yet is the idle. I checked the control valve for power.The ohms and volts where both fine. I checked for a vaccum leak and didn't find any. I checked the overvoltage relay, that seemed fine. The only thing I didn't check was the control module, because I wasn't sure where it was located on a 1990. And I'm not sure what to fix when I find it. If anyone has any suggestions, I would appreciate them! Thanks!

I worked on high idle issue on my 1991 560 SEL for 5 months and finally fix it for nothing.

To answer your specific question, the idle control unit on your passenger side. Take teh carpet off and you should see a black cover and the unit is behind that. However, if you get a good voltage on your idle control valve, your ICU shoudl be o.k.

The very first thing is to clean the idle control valve. Do a search on that one and you will find several well written steps.

I went over everything, even took the car to MB dealer, and could not solve my high idle issue. Finally, I just took the advice and stuck a core with a 5 mm hole into the ICV and that was 2 months ago. The car ran beautifully ever since.

What are the symtoms?

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Steve
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si

Hey, thanks for the info. on the control module. But you lost me on the part with the core and a 5mm hole. Did you mean cork? I would like to find a conventional way to repair the problem first. As for the symtoms, the car idles at about 1200 to 1500 rpm's in neutral and about 1000 rpm's in gear. It's not terrible, but I would like to see it at 650 rpm's where it suppose to be. It also doesn't always fire on the first turn of the key anymore. If not the first time, the second time it will fire. Sometimes when your cruising along around 50 mph it will hesitate for a brief second. I'm not sure if that's related at all. Hopefully, that gives a little input on my problem. Thanks Again!

This is most likely the ICV. Quick and dirty test is to pull the plug of the ICV see if there is a difference. If no difference it s probably the ICV. If there is a difference then start with the duty cycle. There are loads of threads on high idles on 560's, I would suggest spending some time going through them alot may have similarities to your issue.

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Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)

There are a lot of inputs to the idle speed controller and it could be one of many things but the most common are the failure of the "air slide valve" which pumps air into the intake manifold on idle (which is necessary because it uses a mechanical air flow meter that shuts off the intake manifold at idle). When the Air Slide Vlave fails it burns out the control module and they usually get replaced in pairs. The old system had a manual screw type valve. To fix yours, the best way is to replace the two parts described above. How many miles on your car?

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Steve
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si

Make sure that your accelerator linkages/cables are not too tight. They can go tight on you if the Engine mounts are shot.

Also, pull back on the accelerator pedal with your hand. Does your idle speed drop?


Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]

Hey, Thanks again for the suggestions. I've read a bunch of the threads on high idles and tried a lot of the test. I checked the throttle linkage and made sure there was free play. I removed the lead to the idle control valve and the idle did increase. I also removed the control valve, cleaned and lube it. The idle was still the same. Steve, unfortunately I don't have a service manual, but with the help in here I've been able to check alot of things. Hopefully, I'll be able to find the problem with some further help. Steve I was wonder if you can tell me a little more about this "air slide valve" and how to tested these two parts. Thanks Again!

I fixed my high idle by replacing the idle control valve. This is on a 1989 420 SEL. I did test the old one, and it did increase the RPM when it was unplugged.

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1989 420 SEL

The "idle control valve" is the part that the manual refers to as the "air slide valve" which is nothing more than an air pump that functions as I described it earlier in this thread. If the idle goes up, it could be a variety or things like the controller. The idle speed has inputs from the air conditioner too. To really diagnose it you need a break out box and know how to use it.

I took that problem to a dealer before I learned to fix it myself and the dealer said "it is hard to diagnose and we usually have to replace a lot of parts and people don't want to pay". I said "that's me exactly". The dealer said "I will take a pass on that job".

If you want to do any work yourself, buy the manual because it will save you a lot more than it costs and then you will be equipped to do the work. Without the manual, it just takes too much to walk through it.

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Steve
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si