Zimoludek

Hi, So I took my perfectly running 89 S4 auto to a mechanic for oil change, fuel filter change and power steering reservoir hose replacement, after that it now idle (when it warms up it runs as if few spark plugs were disconnected and the oil pressure gauge is jumping all around shortly after the car dies) I also just realized that only one of the two radiator fans is spinning not both (not sure of this was like that prior to mechanic or not), what could they had done while changing the hose that would allow it to act this way. Just like to add that all this was not done at some 928 pros but just a standard shop (not too many 928 experts in NJ). Can anyone help ?

Koenig-Specials 928

Have you checked to see if it is actually running on 1 bank only?

Zimoludek

When car is cold I can start it and drive like before no issue, strong (keep in mind it was 40 F deg. outside today) I was able to drive it about 4 miles and than it states idling. Is it possible that it could run on all cylinders and only half when it warms up ? don’t think so, it does feel like a vacuum leak (had a 79 had the same issue, sold it as I had put too much $ in it and issue still existed) - no one in my area to really help with 928s most mechanics afraid of them.

Mrmerlin

probably moved the coil wire and its loose or touching some part of its run,
NOTE coil wire should not touch anything, and the ends should be clean.

use a IR gun to test what cylinders are hot then swap the coil wires see if the cylinders change.
You might need a new coil wire.
Check the wires going to the oil pressure sender,
and at the 14 pin connector spray deoxit 100 on the pins inspect the wires for shedding insulation

The Forgotten On

^^ I had an ignition amp fail intermittently when warm in my 89 so it can definitely idle fine when cold and then lose half of the cylinders after warming up for a bit.

But I would do what Stan is suggesting and check you coils wires and connections first.