My 1987 305 TPI engine with 51,000 miles on it has developed an intermittent miss. This happens when the engine warms up. I can drive around for about 5 minutes and no problem, then out of nowhere when I'm sitting at a stop sign the engine idle will drop down very low and then stall. It starts right back up no problem and seems to run fine until I have to stop again.

Yesterday when this happened I manually stepped on the gas pedal to keep the idle up so that it wouldn't stall out. The engine then began to miss and backfire very badly and I could smell the rotten egg smell form the catalytic convertor. I parked the car for a while a drove it again. it started right up and drove fine again for about 5 min.

I took the car to a Chevrolet dealer. They checked the fuel pressure, cleaned the throttle body and said they couldn't find anything wrong. they don't have a computer to check my car since it's so old.

I did hose down the engine compartment to get all the dust off from the car being in storage and that's when it seems that the problem began.

I'm used to carbureted engines. I know nothing about the TPI system except that I like how it looks

Does anyone have an idea as to what coould be going on?