[W126 Coupe] 87 560SEC (euro) running problems

[alal30319 at gmail.com]

All

I posted this on a couple of forums but i've not been able to get any
tangible answers so I thought I would cross post here:

Here is my scenario:

When I bought this car, I got it to run like a scalded ape. It was fast and
smooth. I replaced the plugs (NGK non resistor), plug wires, coil, rotor and
crank position sensor.

Recently, I had a bad miss which I've been trying to chase down. I initially
thought it was a bad fuel distributor or injectors caused by bad gas, so I
pulled the injectors and checked them. Some of them were a little weak so I
replaced all 8 and got the car to run very well at idle. But after running
the engine for a while, it would develop a miss on and off and you'd see the
oil pressure gauge drop when it does.

After a long drive, the miss would get worse and become more constant.

I've been able to disconnect the electrical connection to the EHA and get
the car to idle better.

I've checked for vacuum leaks but could not find any. The vacuum gauge on
the dash is pinned to the left until the car develops a miss and then it
will move towards the center (about 1/2 way between far left and center).

I swapped out the EHA with another that I had on shelf but this did not
change the symptoms.

I suspect that it could be the O2 sensors, or the computer trying to lean
out the mixture but I am not sure how to test these.

I'd be grateful for your thoughts.
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