I really like this site and have found a lot of useful information here. Good job, guys.

I was wondering if you could help me with a problem. I see many posts about it, but have one additional point to ask about. I have a 1993 190E 2.3L. Briefly, my problem is:
I have an intermittent Idle Problem: When the engine is warm or hot, low idle (500 rpm) causes car to seem like it will stall in all gears, although the the car has not actually stalled. It runs fine if the engine is cold, or if I put light pressure on gas pedal to raise rpm to 1000 rpm. Acceleration and all other aspects of driving are great.

Removal of fuse on Over Voltage protection relay:
1. prevents a cold start (car left alone overnight). The engine turns over, catches, runs briefly (4-5 seconds), then stalls.
2. Will easily start a warm or hot engine
3. Will allow engine to run normally (idle at 800 – 1000 rpm) in all gears after removing fuse & starting engine
4. Removing then reinstalling fuse and starting engine after hot idle will allow 800 – 1000 rpm idle for a few minutes, but low hot idle will resume after those minutes.
5. ABS lights up on dash ir fuse is removed
6. Situation improves by briefly driving (10 blocks) without fuse for 10 minutes, but I dont want to do that since it likely will ruin the catalytic converter.

My question really is what else does the OVR power besides the things listed on your site? Are there any other suggestions that you can give me to troubleshoot? Thanks in advance for your help.

It sounds as if you have a fuel control problem, when you take out the fuse, you are putting the system into limp mode and thus masking the problem, not making it better. You should have this checked by a tech, even if you want to do the work yourself.
The overvoltage relay does control the fuel, idle, and ABS.

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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

The overvoltage protection relay is sort of like a surge protector for your PC. It provides protection to a number of different control units on different cars.

On yours I think it only powers the KE-Jet controller (and thus idle control) and the ABS controller.

The system was designed to fail in a way that still works well. The two controls that are activated by the KE-Jet controller are the EHA and the Idle valve. The EHA does all forms of fuel correction but it is adjusted properly to zero (median able correction) with all enrichment off. When the ECU is dead it also is at zero so everything works quite well. Since there can be no forms of enrichment like this, the 50-70ma of correction used to cold start and warm-up is affected severely at zero.

The idle valve also has a rest state that allows a higher than warm idle air amount. You could get the same effect by unplugging the idle valve without damaging the cat by also disconnecting fuel control.

The reduction of voltage at the controller drops the control current (should be about 600ma at idle with A/C off in neutral) to around 500ma which drives the valve closed. We have actually watched this. It seems hard to believe that zero current is the rest state of 8-900 rpm but the reduced current of 500ma is a more closed position.

Anyway, if your problem is because of the OVP relay this is what you will see: a reduction of current and a reduced OVP output voltage. It will not be a total failure as that would leave the idle valve in the rest state that you have seen to run the car at a greater speed.

There are many other considerations for the intermittant stalling condition but the above is what we have found with OVP relays when they are the cause.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Thank you for your prompt reply and thorough information. I will take your advice and also have it checked out by a MB tech after the Easter break. I'll let you know what happens. Keep up the good work.

earnest: you gotta like the quality
of those replies. the techques here
knows their stuff!! WELCOME ABOARD!!

Sorry to have taken so long to reply. My laptop crashed, and it took Compaq forever to get it back in shape, but that's for another newsgroup.
I took my 190E to the dealership, and they could not find a problem. As I mentioned earlier (and to the dealership), when the fuse on the overprotection relay is removed, the car will recover for a while before acting up again. The first thing they did was to remove that fuse, and clearly, they could not find a problem since it did not exist. Anyway, they didn't charge me for it, so I can't complain.

I'll bring it back to the dealer and post again when the problem acts up and they identify it. Take care.

Possibly a faulty idle control valve?

You need to check for leaking vacuum hoses and idle control valve hoses and check the idle mixture, also the throttle position switch (wrong mixture at idle if it's not working correctly).

You may also have dirty or worn injectors -- when they leak at low flow, you get an over lean correction problem as the ECU tries to get the mixture right. This causes rough idle and throttle lag on takeoff. Cure is new injectors.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!