I have a 1995 Pontiac Grand Am 3.1 V6 I bought used privately. It has 194,000 miles.on city or country road it run find but when I get to highway speeds it stalls. I drove it recently from CT to Syracuse NY, about 250 miles, no problem. Prior to my return trip the Service Engine Soon light illuminated. I thought it was the cat or O2 sensors so I added a can of cat cleaner. after that on the return trip the stalling started at about 150 miles. I was on NY 84E ( from NY 17 E) and it started to stall it had to stall about 25 times before I cross the CT border in Danbury. It would drive 5-7 miles and stall again. One big hill it stalled after a hundred feet or so and about 8 times before I climbed the hill. It’s in the shop now and they don’t know what’s wrong. Previously I had new plugs, timing chain and water pump replaced at two other shops. My current shop found 3 error codes for EGR and replaced it. This car is a OBD 1.5 I did smell exhaust in the cabin of the car. Now they are going to replace the Ignition module and if that doesn’t work, they are going to replace the computer. ( my A/C and Cruise Control does not work also ). Any suggestions? Im lost on this and the mechanic recalls GM cars had a similar problem in the mid-90s. When it’s running it runs great. Thank You.
Did you check the catalytic converter? Tap on it and see it you hear rattling. It takes a lot of airflow through the engine to keep burning fuel to maintain highway speed. If the cat is broken internally, its contents can shift and cause exhaust to back up into the engine at high speed and essentially suffocate the engine.
