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.

 

The lag when taking off from a stop is what points me towards your injectors.had the same problems.I would hit the gas and the car wouldnt respond for a few seconds then take off.If you havent been reading the thread "Ditch your stock Injectors" you can run that route or try stock ones again.I would also check fuel pressure first and make sure its within specs and then go after the injectors if it checks out okay.

 

Check the timing, too. Have you pulled the distributor cap off?

Code 12 is a "loop" code, just there to verify that the ECM is working. If that's the only code that you're getting, then you don't have any fault codes stored in your ECM. That makes me think that your problem must be caused by something in the fuel system (like injectors), the ignition timing, or perhaps an intake manifold leak.

jstrdn90rs - Could a leaky cold start injector cause this issue?

 

I never messed with a cold start injector ,so I am a novice in this area..I would assume that the cold start injector would just operate during start up and only on start up..any additional would cause a rich condition and in turn would create a lag if theres enough fuel leaking from it.I would check resistance in all injectors and compare them to specs.I know the stock 3.1's are 12 Ohms give or take an ohm.Not sure what the 2.8 are?.and the cold start one is rated at.Also just a note.. pulling the plugs would indicate a rich condition?When I was running my 3.4 injectors it would act like its searching for idle going up and down ..but when I got it on the highway it was screamin.But it finally killed the O2 and never turned a SES light on..

 

Forgot to mention that I had already checked the timing and it was spot on. I had to replace the ignition module about a year ago and had to take the distributer cap off for that. I checked for leaks around the intake with soap and water to see if it bubbled but couldnt find anything. The thing thats so weird to me is the 40 mph surge it almost seems. The car idles up and down constantly for as long as I try to stay at 40 and its driving me nuts. Don't have a day off til Saturday and its my daily driver so I won't be messing with injectors til then.

 

i have that same problem too let me know whats up i personally think its my o2 because i ran w/o a maf for a year.

 

Buddy of mine said it was the 02 sensor as well. I replaced mine just about year ago and im not getting a code for the sensor being bad but we all know that doesnt mean anything. I guess I'll try a new one and see if it helps I just hate throwing a new part on and having the same problem been down that road too many times

 

invest in a scanner..if an O2 goes out usually they just dont go out unless they have a lot of mileage on them or get contaminated with something.Its possible its not going into closed loop cause of the O2 being bad?.If thats the case and putting a new one in solves the problem then you have to think what caused the O2 to fail in the first place?.It might fail again down the road and then its time to find out why.If you dont think you have any issues with the fuel system or a new O2 doesnt help. I would look into a sensor like a TPS its possible it has dead spot at certain throttle setting..its a potentimeter..or I call them swiper sensors.If it has a dead spot..basically an open in the wires the ECM doesnt know where the throttle is at?.cant control the IAC etc.

 

Ive got the same problem well im not sure about the 40 mph thing, but if i find out whats wrng with mine ill chime in and let you guys know.

 

My problem turned out to be the o2, i got a universal heated o2 though because ive got headers and my o2 sensor is further down the exhaust than stock. But i would put money on it being the O2

 

Did your car like chug alittle at idle when warm and did it take a few seconds to start cold? thats my problem

 

it had no problem cold starting, my thing was it woukd start then diei could keep it going until i was warmed up then i was fine. Also when taking off from a stop the car would jump like it was gonna go somewhere then just slowly take off, along with crapy idle and rough acceleration. But all thats fixed now