85 380se fast idle?

[mgerdes]

what would cause the idle to just start racing for no reason? i will be stopped at a light and idle will jump from 600 or so to about 1800. gets kind of scary. sometimes if you restart the car it will go back down to normal and sometimes it wont. you can drive to the next light and it will be normal again. very unpredictable. seems to be no pattern. seems to do this about 25% of time. hot or cold.cleaned throttle plate, no effect. nothing else seems out of place. help?

[Q]

Been there, done that with the same exact car. The problem is your Idle Speed Control Module. The black box between the two firewalls, just about dead center. The thing is about the size of a sandwich.

If you take it out and pop the shell off, you can resolder the board and fix it for free. Search the forum. I have posted the technique before.

[mgerdes]

thanks q, i can do that!! how about getting the heater to shut off! im betting its a heater control valve, got hot air all the time. any ideas?

[grey500se]

I have the same problem on my 500SE Euro, I'll try that out, thanks

[mgerdes]

tried it last night, touched up the board, did not help. noticed new part is almost 200.

[grey500se]

man, that sucks, I hope I have better luck

[Q]

mgerdes,

Did you liquify all of the joints? If all of the solder doesn't flow, you might not get the corroded joint to connect. The real trick is the flux that is in the solder. It will clean the corroded contacts.

Sorry it didn't work for you. I found that my difficult starting was resolved by this procedure as well.

[mgerdes]

your right , i may not have got them all, took the board in my hand while it was running and the idle jumped all over the place, especially on two square caps. hands on, racing engine, hands off, normal idle, very sensitive to touch, i will try touching the joints again tonight, running good right this minute. should also say that someone has run a ground from the plug to the chassis and cut the factory ground. some tech is aware of this problem.

[mgerdes]

mr Q. seems the second time is a charm, so far working just great, has not acted up. thanks. mark