1986 Firebird 2.8 v6 mpfi



When I am trying to cruise at 40mph the engine idles up and down without me doing anything with the throttle. It will do it for as long I try to stay at 40mph and hold it there. I can throttle through right on past without a hesitation or a difference in engine idle. The car has also had poor low end throttle response and I guess you would call it lag when trying to accelerate from low speeds or a stop. Don't know if it's related or not but its been backfiring when I accelerate hard from a stop or low speeds. I'm only getting a code 12 when I check the computer, I thought that it might be a vacuum leak but I checked and there isnt a leak. I've been told 02 sensor but its less than a year old and I don't think its the problem. I'm leaning towards old dirty clogged injectors and was wondering if I'm completely off. Thanks.

 

If it has high mileage I would check the timming chain. Sounds like the timming miight be slow.