In all of the above, one thing stands out: there is no mention of the fuse in the OVP relay. Has the fuse(es) been confirmed good?
As a check on the OVP relay as the culprit in all of the travails, remove the relay and bridge the pin sockets that correspond with circuits 30 & 87 on the relay. Those pins will typically be #1 & 2. If the relay is at fault, operation should be normal.

My bad, I should have included that information. Yes, the fuses were checked in both units.

The IAC valve is jammed up solid. It has been set for over six hours with penetrating oil and still nothing. I've tried a 9v battery and no joy. I have a new one coming.

Thank you for your input.

When all else fails, read the directions; all of them.

I assume you tried the voltage in both polarities, just to be sure. a momentary bump should not be a problem but should cause a movement. Try 12v. If that motivates it the controller card is suspect and those can be hard to find.

After reading your post I recalled reading that another tell of a bad OVP is an ABS dash light turned on. The light does not come on. o I figured it w ikely OK.

Yes, I tried it both ways. I even picked up a new battery. No good.


So I'm setting here scratching my head, and elsewhere, when it hit me. I dumped the penetrating oil and filled a container with Simple Green enough to allow me to soak the rotating valve end. Two hours latter the battery got it rocking! Every time the battery sparks, it moves the valve. Checked polarity both ways, worked each way.


So I shook it out real well and hit it good with carb cleaner and tomorrow it gets reinstalled.

Reinstalled the ICV and the engine fired right up. Lasted for about 20 seconds. The engine just stopped. So I jumped out the OVP and still no go.

I then pull the ECU and it is marked 005 545 2132 and 0 265 101 018. I have found posts about these failing. So I have a salvaged unit on the way.

More to come for sure.

0 265 101 018 is ABS Control Module .

It should be here Wednesday. It's the cheapest component I've bought on this rebuild.


Thank you to those that replied.

ESL (English as Second Language) ?

OR

NFL (No First Language) ?

NO. Just the fact that all of the terms refer to the same unit.

I'm still putting it back together, but I finally found what is likely the issue. The small hose on the idle air valve was torn at the housing end. Looks like an old tear as there is dirt in it. Also, it looks like the plenum was leaking around the edge at the FD end. All around the edges, there is an oxide residue and where I suspect it was leaking is almost spotless.

Who knows the secret of getting the FD back on the intake with a new plenum rubber?

The saga continues. I got the FD mounted back on the intake. After examining the MB unit, I had to take a knife and bevel the edges of the new plenum. I buttoned everything up and gave it a try.

The engine will run, and it runs like a scalded dog. It will not idle. At about 1K RPMs, the engine dies. Just turning the engine over will not get it to start. I have to put my foot into it and I can, on occasion get it to start, but it fails again.

I confirm the engine is getting fuel. When the engine dies, I can open the fuel line to the FD, and fuel, under pressure, comes out.

The IAC is clean and the rotor/valve moves freely using a 9v battery. The plastic cable end is shot and the wires may have not gone on the proper terminal, so I tried the wires both ways. No cure.

Everything I can find on the web says that the ECM (computer) controls the IAC. I have picked up a salvaged ECM and swapped it out for the original. No go.

I have 3 FP relays and have tried each one, No go.

I have 3 OVP units, all with good fuses, No go.

I have not changed the O2 sensor. Nor have I changed the FD potentiometer. As I understand the system, these will affect performance but are not "no run" issues.

When I was able to get the engine running, the dash "economy" gauge would set just off the left peg, and when I increase the RPMs, the pointer will shift right. When the engine is off, the needle is pegged right. As I crank the engine, the needle stays pegged right and does not move. I have checked every air connection and everything looks good, all connectors fit tight.

The FD air plate is set at 2mm free-play. What info I get off the web says the free-play should be from 1 to 3 mm. Could this be as simple as the air/fuel mix setting?

Any thoughts are welcome.

I'm going over everything again and this one comment hit me. From what I can get off the web, the IAC unit is controlled by the ECM (computer). What is the controller card you refer too?

1988 300SE ... that would be W126 gen 2 ... I have never owned that. The gen 1 models had things like this:

https://www.programainc.com/item_list.aspx?q=300se%20mercedes

But your electronics may have moved it to the main computer?