450SL idle problem
 

79 450SL I had a high idle problem- when my 450 was cold it would idle at about 1800-2000 rpm's for about 10 minutes, then drop to normal. I removed and cleaned the airflow sensor plate, replaced all vacuum hoses, replaced the auxiliary air value, this corrected my high idle problem. Now after my 450 warms up, it will not idle. Could this be a fuel related problem. Jim

How does it run when cold after your changes? Does it still idle high for awhile (normal) until warms up?

After 450 warm's up rpm fall off and motor just quits.

I wonder if ALL the air that it is getting is from the auxillary air valve. Maybe when you cleaned the airflow sensor plate, something got screwed up.....

I have an '84-380SL with the same symptoms. No one on Vancouver Island can diagnos or treat my Benz without quoting mega $$$$$ or the preverbial 'shotgun' cure (everything is replaced). I am so happy that I have several motorcycles and another car to depend on and some friends that will pick me up on the freeway when my car stalls. I found myself turning off of the freeway to 'stall' and then turning back onto the ramp (U-turn in mid highway) to avoid the signals and avoid the enevitable stall. Is this a way to live?? I surely hope you solve your problem and all of us out ther will be very greatfull. Thanks.

When I have had this problem on other CIS cars it turned out to be a major vacuum leak.

Thanks Speedy and the rest of you. A friend suggested that if I suspected a vacuume leak to spray WD40 at the location and if the idle sped up it would point to the leak? It's worth a try? Much cheeper than replacing everything if it works.

Ignition control module
 

I spent over a year chasing intermittent idle problems and stalling. My stalling problem turned out to be the Ignition Control Module. It's in the driver's front fender well and attaches to the coil. Mine was fine until the car warmed up, then it would die. I found it to be hot and after borrowing the same one from a neighbor's Mercedes, it ran fine. Run the car until it dies and check if your ICM is hot. Also, both mine and my neighbor's were held on by two fasteners but were loose. I think it banged itself to insanity. Now we have three fasteners.

my guess is it has something to do with the work that was done. In a case like that I replace one thing at a time. It takes longer that way but you have a basis for when things changed.

Hi Fellas. Steve, I tried your recipie re: the hot idle module. It was Luke warm. We Canadians are metric and bi-lingual so I'd like to know what "hot" is in American? It did start out to be cool to the touch but I could hold my hand on it with ease when the car stalled. What constitutes hot? Thanks.

I was told it is supposed to get hot but I think it means warm. Mine was hot enough to fry an egg. I guess it is not hard to tell if it was as hot as mine but I do not know if it could be bad even if it's not so hot. The problem is that you can't return electrical parts. It would be great if someone could loan you one. Got any friends or neighbors who have a similar car?
After re-reading your problem, I think the difference in symptoms is that mine would run fine after warm-up but after running it another 20 to 30 minutes it would die. Yours dies at idle as soon as it warms up. Regarding the Idle air valve ("Air Slide Valve") the electronic module that controls it could be faulty as well. I read (here in this forum?) that the valve starts to go bad and the module pulls too much current and burns up the module. It said the valve and electronic control module should be replaced together. I don't recall a test procedure for the module but I think one exists. Other than normal tune up parts or fuel injectors, I'm stumped. I replaced my fuel injectors at 115,000 miles and it made a world of difference. The idle is more stable. Keep us posted.

Hi Fellas. Steve, there are very few SL's in Campbell River and none of my friends have one so your idea of switching parts hits a brick wall. I was thinking that IF I did borrow one to try wouldn't that be asking the lender to gambol on me trashing his unit just to find out if I had a problem. I may end up buying a unit for my car and one for his . . . plus a case of beer . . or something. Anyway, I am heading back up north until Xmas to work and I will just put the lid on my SL, lock the garage and keep tuned to this channel for late breaking news from the 'experts'. It was a good summer for 'top down mode' here on Vancouver Island . . . so I took my hat off! (hehe) Maybe I'll have some luck at Xmas?? Thanks again for your help fellas.

Hello, MB Friends and fans. Jack, it doesn't have to be a SL because the module also goes into the SELs and any Mercedes with that motor. I borrowed one out of a 500SEL. I also promised the lender that if I burned his up I would replace it. MB wants something like $800 for it but I bought it here for around $375. I didn't burn up my neighbors unit, thankfully. I wish you the best of luck. My local MB dealer wanted to "take a pass" on these problems. He said that they "usually have to replace a lot of parts and it costs a lot of money and people don't want to pay". I said "that's me exactly". Then he said he would pass. I figure that I can replace the parts myself and source them for less so even if I replace a couple of good parts I am still saving money. I kind of enjoy the challenge, in a twisted, masochistic sort of way.