'89 W124 300TE, rough idle, fuel issues, engine light etc.

[BRM]

I picked up this 300TE a few months ago and over all haven't had to many problems with it. It has occasionally had an issue where at idle or while driving it would start stumbling and running rough then would clear up. Each time that this happened the engine light would come on and go off once the problem cleared.

The car has 95,000 miles and recent work performed include new Bosch Alternator, relays, fuel pump relay, new cap rotor, plugs and wires(all Bosch).

I have done a bit of reading up online and in a manual I have, I have consulted with a few shops that I deal with and narrowed down to troubleshooting several specific things.

Recently the problem worsened, the rough idle became permanent and would stall. The air flow sensor plate was out of adjustment, after correcting that it ran better but the problem came back shortly after and the engine light came on permanently. Soon after, cold starts became an extremely difficult ordeal and it continued to run rough and lack power during driving.

A visit to a local shop resulted in an adjustment of the fuel air mixture, it ran significantly better and the engine light went off. However the fuel/air was not able to be adjusted within spec on the tester indicating that the oxygen sensor may need replacing. The existing oxygen sensor was replaced as it looked to be original. The car seemed to run better after that however the problems returned on the drive home.

The following morning the car would not start. I finally got a very low rough idle. I adjusted the fuel/air a little until the idle picked up and smoothed out better. It still idled rough, it did not transition well from idle to higher RPMs and it would occasionally stall. I did some poking around and disconnected the plug from what I think is the EHA valve on the side of the fuel distributor and the idle dropped slightly and smoothed out although it is still a rough idle. It runs significantly better at all speeds with the plug disconnected. The engine light remains off more than on. This morning it had a very rough idle until it warmed up and then it ran great afterwards.

I have checked for vacuum leaks and found none, I have run this car on premium gas as suggested although I do not know what the PO used. The E.H.A. valve shows no signs of leaking fuel.

I feel like I am on the right path in figuring out what this issue is but I figured that now would be a good time to see if anyone has had a similar problem and take suggestions from the more knowledgeable members.

Thanks in advance.