Does anybody know the correct idle speed for a 1985 500 SEC. The idle speed on mine is between 450 - 500 in park, 350 - 400 in drive. I think it is a little low, and the motor shakes a little because of it. If anyone would let me know the idle speed AND how to adjust it, i would appreciate it!!

New idle control valve, idle control box, ovp, fuel pump relay, fuel pumps, injectors.

Should be an emission sticker on the core support that gives the correct idle speed & engine timing as well.
Correct idle speed should be 600rpm +-50rpm.

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Is there any way of adjusting the idle speed? I've searched for other threads but cant seem to find any explaining how to adjust idle speed on this car.

Thanks

I believe it's like the 380, and the answer is "I don't think so." It is electronically controlled. About all you can do is make sure that the various components are working correctly. I can send you the procedure for testing most of them if you send me an email.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Idle speed is electronically controlled; or should be.

At the front of the aircleaner, underneath is the cylendrical idle valve. Disconnect the electrical and the engine should rev to 2000rpm or more. If it doesn't rev, then the valve is stuck or the passage orifaced. Common bypass to the electronic control problem is to put a piece of broom stick in the pipe with a 4mm hole bored through it. I have found three or four.

There is no adjustment. If the valve is actually being controlled to such low speeds its likely a control unit problem.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Steve,

Had problems with the idle about 2 months ago. The idle was surging to almost 2000 rpm, replaced the idle control valve after checking it by pulling the electrical connection and noticing no difference. That didn't fix it. Replaced the idle control box about 1 month ago, that fixed it, also checked the idle control valve again after replacing the idle control box and it seems to be working. Pull the electrical connection and the engine surges up to 2000 rpm. Also replaced fuel pumps, fuel pump relay, ovp, fuel distributor, fuel lines, fuel filters, and injectors, but the idle is to low and a little rough. Also, if i switch the a/c on, the idle smooths out and you dont even know the car is running. I've checked all the vacuum lines, injector seals (brake cleaner test) and cannot find anything out of place or any leaks. The engine runs excellent otherwise, great accelleration, smooth when driving at any speed, no problems at all, just this pesky shake on idle. Any suggestions would be great!

Thanks

I might suggest that you fool the box into thinking the AC was always on.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

That would be great, how would i do that?

Steve,

Could you tell me how i can fool the box into thinking the a/c is on?

Thanks

You need to look at the wiring diagram and see the connection between idle control and the A/C. Then monitor that connection while the A/C is on. Then reproduce whatever signal is recieved. Probably only ground or battery voltage but it could be a 5v signal. That might be a little harder.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks Steve, i'll see what i can find out