I've got a fast idle problem on a 420sel, year 1986, and I have some questions about the "idle control valve".

How do you determine that this valve is working, how do you test it?

How do you clean it......what solvents are best, how and for how long do you soak it, and how do you know when it's clean enough?

Thank you.

Does it idle fast only when the A/C is on? There is a connection between the two I think.

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Ed
1981 300CD (Benzina)
1968 250 S (Gina) 266,000 miles!
1983 Alfa Romeo GTV6 (Guido)
1976 Jaguar XJS-saved a V-12 from the chevy curse, what a great engine!
1988 Cadillac Eldorado (better car than you might think!)
1988 Yamaha Venture (better than a Wing!)
1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
1981 Yamaha VX920RH (Euro "Virago")
Solex Moped
1975 Dodge P/U camper


"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"

Do you mean the car does or does not idle fast? What exactly happens?

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Dieter

1987 420SEL

I removed mine and sprayed it throughly with carb cleaner. I did not soak it as there is an electrical connection (mine is a 300E). After spraying the internals, I used compressed air to blow it dry and reinstalled.

Hope this helps.

Use carb and choke cleaner. I used a vise to hold the valve in such a position as so I could fill the valve portion with the solvent. I let it soak for several hours. I agitated it repeat, rinse, repeat until there are no more carbon particles comming out. Try not to soak the coil part of the valve. Doing so made a major improvement in the operation of the valve.

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k

I know this isn't the most scientific way to test it but it worked for me. Remove the hose on the front end of the valve and you will see the mehanism inside the valve which should move when activated. Notice the position. Turn the ignition switch on and check the position now. If it didn't move, start the engine and check again. There is also a way by jumping certain pins on the idle control module harness, but I forgot how to do it that.

Does the valve vibrate when the engine is running ??

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k

Many thanks for the responses. Here is what happens: When the engine is started from cold, and the transmission is in "Park", the rpm goes up to around 1200 and stays there. Even when the engine has warmed up, the rpm remains steady at 1200. It is not until I put the transmission into gear, and load down the engine, that the revs drop down to around 900 rpm. After driving the car, and then coming to a stop, the revs will settle on 900 and sometimes will drop down to 800 rpm.....but never below 800. Turning the a/c on or off doesn't seem to make any appreciable difference.

It's my understanding that idle speed should be about 550 rpm. The last time I had the car to the dealer, the tech. noted the fast idle and guessed it was due to something electrical. Since then, I've learned it can be a host of things, just pick where you want to start.

I have removed the idle control valve for cleaning, so I don't know if it exhibits a vibration when the engine is running. I gather that if you can feel it vibrating, then at least the electrical part of it is working and the question then becomes: "did you clean it good enough?".

I think I now have enough info. to keep me busy for awhile........and I'm grateful to all that responded. Bill

William, this is a classic sign of three things that will make that happen. First is the OVP relay. If your ABS light is constantly on, then the fuse is blown or the relay is bad. OVP is in the fuse box with a red 10amp fuse. ($50). Second is the idle control valve. If it is bad, replace or clean it.($200). Third is the idle control module. It is the small black box on the firewall. ($250). These three things work together to control idle speed. If one of these is bad you will get the high idle before you put it in gear. If you disconnect the two prong plug on the idle valve and get the same results its probably ok.