1987 560sl high idle back
 

Well it seems my high idle (1800 rpm) issue is back, started this morning andwon't go away! Before, (last week) I followed some advce/tips, and re-soldered connections on the idle speed control module and the high voltage relay, removed and cleaned the idle speed solenoid, and between all that it was fixed! or so I thought, maybe I missed a bad solder joint on the module, or maybe the idle speed solenoid still crudded up? The idle speed solenoid was pretty clean when i took it off, I applied 12 volts to check it's operation and even blew in one side of it to make sure it was "sealing" good when energized. Any more ideas anyone? (I'm sure I missed something, as all of you advice was expert, probably something on my part)
Any more suggestions would be just too cool! Unfortunatly I have to drive thecar to work like this, my "86 Plymouth Reliant is being used by my son for school. I'm sure driving it like this is not good and it is also a hassle/probably dangerous!

Thanks,
Dwight Daymen (userID ddayme)

Addition to above: may not br related, but ever since I've had this car, 5 years, the a/c compressor would not come on unless i unplugged the conector on the temp. sensor? (it has two prongs/wires) and plugged it back in a manner where only one wire was connected to it.

Thanks,
DDaymen

The idle speed control unit is the most likely problem, if it is getting power, ground, & RPM signal at pin TD.

What would pin TD be?
Thanks

TD=RPM signal from the ignition module.

Should be around 7.5-8Vdc.

If that signal was missing the fuel pump relay wouldn't allow pumps to run as well.

I guess I'm confused, as I don't know where the ignition control module is. Before, I re-soldered some solder joints on the idle control module, cleaned the idle speed solenoid, and that fixed it for 3 days, then it suddenly came back. One reason I can't check the various voltages to the module/from the module is that I have no schematic/repair literature/pictures, so I am kind of working "blind", I would order a factory repair cd, but unfortunatly it is not in my budget (the hospital where I work has cut our hours down to 3 days a week!) I guess I will have to wait untill I can get a repair cd to effectively repair this problem!

Thanks for the help,
-ddayme

I redid everything I did before, clean idle solenoid, go over solder joints on idle speed control module, but no effect! just that high idle. Somewhere in this website I saw mention of where you can get a re-built idle speed control module, does anyone know the name of this place? I may have to try replacing said module, and it will have to be a re-built/used one.

Thanks,
-ddayme

Before buying anything, try this. With the engine running, move, shack,twist, push on, or pull on the plug at the idle control unit. I went through every thing you have already done and still had problems with my 500 and after doing the above, found one or more of the signals wasn't making it through the plug. I very carefully removed each wire from the plug (make a chart of wire colors to location before you begin) and close each one up just a little. Spray just a little WD-40 or contact cleaner in each hole and replug and test again. Mine has been working great now for the last 2 years or so.
This is the first thing I do now if I have problems with electronic components. It is the best way to find bad solder joints and connectors.
Good luck,

Paul

You applied voltage to the solenoid - did you check to see if the wire you're connecting to it had any voltage coming out of it? No voltage to solenoid = high idle.

Yes, I checked the voltage to the solenoid, it was only .008! not right, I,m sure.

Bad OVP relay??

Re-soldered it, that was one of the things I did, but Maybe I missed something, I will remove it again and check the solder joints. Wish there was a way to check these out without replacing them/swapping with known good ones!

Bad 10-amp fuse in the OVP red-topped unit?? BTDT, $1.00 part.

Idle control unit just might be bad. Just because you re-solder connections doesn't mean the guts are going to come back to life.

OVP could be bad, too, but you should be getting an ABS light. Don't just visually check the fuse on it, either - ohm it out. I've seen plenty of fuses that look good that were "popped".

Some of the inputs into the ICU include vehicle speed, rpm, engine temp, compressor enable, idle input, and most importantly - ground. Bad/dirty grounds cause more "strange" problems than anything else.

When I re-soldered the idle control module, the car worked for 3 days, but that may have just been a coincident. I checked the fuse on the ovp with an ohm meter, it was good, maybe there is a bad ground somewhere< any ideas where to look? as far as the anti-lock light it does not light up at all, just an unmarked light next to it. I had read about a ground by the coil, but wasn't sure just where that ground was.
Didn't get home till late, didn't even look at the car today!

I wonder if that "unmarked light" is where the ABS indicator is supposed to go...

Try unplugging power to the ABS unit to see if that brings the ABS light on.

I had been tol aqnd had wondered the same thing. Where is the plug/connection for the abs?

I have no idea, but it'll be whatever wiring is going to the ABS unit. Should be mounted on the left side (US passenger side), and should have 4 roughly 1/4" steel tubing lines coming out of it.

Disconnecting a wheel speed sensor should have the same effect as well.

Sorry I can't be more help, but I'm still new to the MB scene and I've yet to do anything more than pay attention to my engine (I haven't even taken the wheels off yet!).

I will look for the wires now to dis-connect the ABS. If I do need an idle speed module, I wonder from what different years/models would work? Also, if, god forbid, it is the ECU, woulden't there be other problems as well? does the ECU or main computer or whatever have a fuse, or does it use the OVP for that (probably a stupid question) The fuse panel cover has been mis-placed, and I cannot remember any of the fuse designations>

Thanks,

DDaymen

I removed the plastic cover from the ABS unit, unplugged the wiring harness, even removed the two relays, still no ABS light, not with the key on, or the engine running!

Also, there is a ground strap from the ABS unit to the frame, which i made sure is getting good connections. I also made sure the pins on the plug going to the ABS unit, as well as the pins on the relays were clean, no change, and the unmarked light is to the left of the ABS light.

Did you try driving and braking hard? The brakes should react like you have no ABS system (which I prefer)... If the light doesn't come on after that, it could be burned out.

I think I got it fixed (again!), will post tomorrow what I did/find etc (involves ABS/OVP relay).

DDaymen

Well I removed the OVP relay, double checked thwe solder connections, removed the relays on top of the ABS, checked to make sure all the connections going to the ABS were good, replaced the fuse in the OVP just to di it, and the car started right up , normal, no high idle. This morning on my way to work, I stopped to get coffee, when I started the car up it went to high idle again! when I started it up to come home, it idled normally the when I was at a light near home, the idle jumped up again! when this happened I heard a "click: from where the OVP relay is, now after several starting times it still idles 1800! I wonder if there is some kind of "short" or rubbing wire to the ABS, or OVP relay. also, when it rains there is a drip by the fuse panel, I wonder if it is getting wet behind it or behind the OVP relay this is getting crazy, works one minute, then starts high idle the next. I wonder if I,m on the right track, maybe just a little off on what else I should be doing. I don't think it is the idle speed control module. Also, the ABS light never lights up, just the one to the left of it that has no marking/symbols, like some kind of extra light. I wonder if this unmarked light is supposed to light or did someone have the instrument cluster out for some reason and got the lights switched around?

Long post, I know>

Thanks,
-DDaymen

I think I have narrowed it down to something involving the OVP relay, when I started the car different times today, all was well untill I turned something on, the I could hear the relay "click"--then high idle!
I was reading some older posts which described someething like this, like maybe a not-so-good ground connection foe the OVP relay, or even the hot wire to it. In the morning I will take a close look at the socket for said OVP relay.

Sure as heck hope I'm on to it!

-DDaymen