My car has recently started to run real rough. Let me explain: When the car is first started up it runs great through all the gears. After a couple minutes it starts to act up. When I go to press on the gas the car hesitates..and it runs real rough like a plug wire has fallen off...and continues to, till around 2500rpm where it does smooth out...and run like normal. If I am cruising along in OD and lean into the gas it bucks and runs rough real jagged and off balance...but then if I let off just a little it will smooth out and all the cylinders are in unison..I am guessing it is electrical and not mechanical. I have ran injector cleaner through. no change. Can anyone decipher my problem. Everything that is listed in my mods was done and running fine for a year before this problem came up.
The plug wires are less than a year old same with cap and I just replaced the coil about a week ago because the car backfired due to this problem and apperently fried it. The coil I am curently using is oem from autozone.
The problem would not be so bad if it happened all the time and did not smooth out that is where I am stumped. Help?

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91 Firebird 305/TBI - cam:.420/.442 204/214 - Hooker 1 5/8" headers - TFX PaceSetter Cat-Back - 3.42's Auburn Pro Posi - ASCD Ram-Air hood - Polished Formula Wheels w/Futura's - Open element - .5" Corian TB spacer - Lakewood LCA's - Hotchkis Lowering Springs - KYB Struts/Shocks - 14.78 @ 97.5 mph(G-Tech) - MacEwen MotorSports Whiteface Overlays - 412ci sb waiting to go in this spring.
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ideas?

 

It runs well when cold because the ECM is in open loop mode. It's that way when the engine is cold. After a couple of minutes, the O2 sensor is hot and a little while later, the coolant is hot enough for the ECM to go into closed loop mode. When that happens, the ECM begins controlling the fuel, timing, and EGR according to what the various sensors are telling it.

I'll bet it's your TPS (Throttle Position Sensor). It is usually the first to go because it is a potentiometer with sliding contact points. Those wear down quickly and start sending bad info to your ECM which, in turn, makes your engine run lousy. I'd replace the TPS and O2 sensor. Be sure you disonnect the fuse to the ECM to clear the memory after you replace those parts. That ought to fix the problem!

 

If the TPS was bad should I not be getting an error code SES light? I understand open closed loop operation but I do not believe the engine is going in to closed as fast as the problem appears. The car only runs good for maybe a minute...does it not take longer for the ecm to switch from open to closed. It is about 30 out and I know my coolant can't be up to temp yet. Can someone explain the symptoms of a bad tps?

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91 Firebird 305/TBI - cam:.420/.442 204/214 - Hooker 1 5/8" headers - TFX PaceSetter Cat-Back - 3.42's Auburn Pro Posi - ASCD Ram-Air hood - Polished Formula Wheels w/Futura's - Open element - .5" Corian TB spacer - Lakewood LCA's - Hotchkis Lowering Springs - KYB Struts/Shocks - 14.78 @ 97.5 mph(G-Tech) - MacEwen MotorSports Whiteface Overlays - 412ci sb waiting to go in this spring.
My Homepage