Hi. I have a 94 C4 that mostly runs great. The only time I have a problem is when the outside temp is warm and the engine temp (on the digital guage) is around 230 degrees. At that time if I come to a stop light and am sitting still the idle will stumble and surge. The car will actually buck a little at times. The car has 80k miles and is an automatic. Off idle car runs and pulls great. At first I thought it was a heat issue so I replaced the water pump and radiator (the analog would almost show pegged). That didn't fix it. I replaced the IAC (inexpensive ) and no luck. Also replaced the coil wil a MSD (found on clearance for $20). As far as I know the car has never had a tune up. So after talking to a few friends, with mechanic backgrounds, I reluctantly agreed it may be the Opti. It wasn't. Also did plugs and wires at the time. Anyone have any thoughs. At this point I feel it may be the ecm. That when the under hood temp gets high it gets flaky. Any thoughts? Thanks.