Rough idle - electrical?? - PeachParts Mercedes-Benz Forum

jaoneill · #1 08-24-2008, 10:37 AM

While sitting at a traffic light yesterday, the '87 190D idled down to an almost stall rpm and of course shook like an out of balance clothes washer on the spin cycle. Tach read zero. On down the road tach began to function, stopped in the next town and all was working. Later in the day at 65 mph tach went to zero again, when I stopped had the same low/slow idle issue. Problem recurred intermittently all day.

Electrical issues are not my forte; any ideas? - RPM sensor? is there an idle control module? a connector somewhere with a history of failure?

Any help greatly appreciated.

Jim

Jeremy5848 · #2 08-24-2008, 11:05 AM

Does the '87 190D (what is that, a W201 car?) have the Electronic Diesel System (EDS) like the 124s? That could be the source of your problem. The fact that the tach also stops working suggests that something in common has failed. I would start with the over-voltage protection relay and then the EDS electronics. Where they live in a 190D I do not know. Someone else here should be able to help.

Jeremy

Shorebilly · #3 08-24-2008, 11:30 AM

Behind your battery, there is a plastic panel.....remove panel and you will find the EDS (I think that's the name of the black box) Module......

I had a posting here related to an in-op tach on my '84 190D, 5 speed.......I can't find it.....

I don't feel like pulling up the Shop Manual at the moment......but this is a kinda odd area of the schematics......I think that the California Models also had an EGR Module in the same general area......automatic cars may be different from mine as well

Phil sells the EDS Module.....it's a bit pricey......

Try removing the Black Box.......if it solves your problem.....with the idle......(removing it prevents a signal from getting to the tach).....I don't know, but if I remember correctly....it looked as if it would not actually effect the AC, however the black box is supposed to take the AC into consideration.......

If you pull the box, and are satisfied with the operation of your car....I can go out and check the pins that I have jumped to get my tach to work....

Honestly, my car came with this EDS Module piece missing and the AC appears to be electrically by-passed.......I have not yet investigated the AC system......

I hope that this has been somewhat helpful to you......I'll try to find that thread......

SB

jaoneill · #4 08-24-2008, 11:44 AM

SB!
Thought that it must be electronic due to the intermittent nature. I have some honeydo's in progress, but will look for the EDS this afternoon, probably the problem.

Thanks again,
Jim

Shorebilly · #5 08-24-2008, 11:57 AM

This should get you to my old thread.....plenty of discussion of this......and some really good pin info for the module......

www.peachparts.com/shopforum/showthread.php?t=228264&highlight=190D+Tach

of not search "190D Tach"

SB

jaoneill · #6 08-24-2008, 01:42 PM

Quote:

Originally Posted by Shorebilly

This should get you to my old thread.....plenty of discussion of this......and some really good pin info for the module......

www.peachparts.com/shopforum/showthread.php?t=228264&highlight=190D+Tach

of not search "190D Tach"

SB

Started an shut off car 6-7 times, let it warm up, start and off again, numerous times - did not replicate problem. Pulled the module and it acted exactly as it had intermittently yesterday. Read your old thread, good info there. Pulled module from '84, thought I would swap but it is different (4 cyl to 5 cyl, different #'s). Cleaned up one slightly corroded pin receiver, may solve the problem, if not, I will get with Phil for a new module.

Really appreciate the help,
Jim

jaoneill · #7 09-10-2008, 07:16 PM

Got a new EDS from Phil; did not solve the problem. Have driven over 4k miles since last post, same intermittent issue with either EDS (new or old). Only time things worked properly (and steadily for any amount of time) was when I was on the interstate, cruising at around 80 mph. I suppose the next question might be, what, or where is the sensor/sending unit that might feed the EDS?

Went back to Shorebilly's thread and it appears that the ac control module may have something to do with the problem. Anyone have any clue where I might find that?

All thoughts welcomed,
Jim

Jeremy5848 · #8 09-10-2008, 07:40 PM

I'm not really very confident of that a/c suggestion. How about the over-voltage protection relay? It "protects" the EDS and some other sensitive electronic systems and can cause problems if it goes flakey. The OVP relay is a small box with a fuse on top; it usually lives in the same area as the EDS electronics (but I don't know where that is in the 201 cars).

The only other thing that comes to mind is a couple of bad spark plugs.

Jeremy

jaoneill · #9 09-10-2008, 08:07 PM

Quote:

Originally Posted by Jeremy5848

I'm not really very confident of that a/c suggestion. How about the over-voltage protection relay? It "protects" the EDS and some other sensitive electronic systems and can cause problems if it goes flakey. The OVP relay is a small box with a fuse on top; it usually lives in the same area as the EDS electronics (but I don't know where that is in the 201 cars).

The only other thing that comes to mind is a couple of bad spark plugs.

Jeremy

Is there any way to check the OVP relay? Although the fuse looked ok, I changed it early on, thinking that perhaps it was the problem.

Changed the spark plugs and points just a few weeks ago

Jim

babymog · #10 09-10-2008, 08:42 PM

Sounds like the OVP relay. The relay behind the battery with a clear cover and fuse on top. Fairly common, usually takes out the tachometer and idle, as well as the ABS.

jaoneill · #11 09-10-2008, 09:06 PM

Thanks guys, I'll give that a whirl

jaoneill · #12 09-16-2008, 07:42 PM

Thanks guys, OVP relay did the trick.

Jim