Let me start by saying I've read every stalling and hesitation thread on this site regarding w124s but the problems are so varied I feel I need direction.

My Mom's car, '89 260E has had an intermittent stumble with check engine light for a year. It will happen while she's running errands and then the stumble will just clear up and the light will go off. It has died on her once which leaves me concerned. The car has 199K and the only thing that doesn't work is the AC (saving that problem for later).

I've had the car all week and gave it a thorough once over looking for obvious stuff. I replaced a corroded negative battery lead (which I initially thought was the problem), idle control valve, and fuel filter. I've proceeded to put 300 miles on it this week with no problems! I gave it back to my Dad this morning triumphantly declaring that it's fixed; an hour later I get a phone call and he tells me he's sitting in the car staring at the check engine light and listening to the engine stumble!!

Being a Mech Engineer, I feel I'm qualified to fix the darn car if I can figure out the best way to proceed. I have an extra OVP relay, fuel pump relay, and ECU for this car but I don't want to swap anything unecessarily. Maybe the O2 sensor?

My other car is a 500E and I've successfully troublehooted all kinds of gremlins. I made the code reader on Jim F's site and it has been invaluable on that car. Will it work on this '89 260E? Is the code list the same? I need some direction! Please help me fix my nice Mom's car!

Thanks in advance,
Gregg