hawkeye18
Sorta cares
Ok, so my 95 atx has what feels like a misfire at idle, every about 5-20 seconds or so. When it began, it would only do it with the AC on. Now, it does it all the time, but is worse with the AC on. It gets worse as the car gets warm.
I put a new AC clutch in, figuring the AC pulley bearing was bad. Still does it. Swapped the two idler pulleys with known goods. Still does it. All other pulleys spin freely and queitly. Pulled codes, got a 551 for "IAS" bad. Hey, look at that, the connector on the back of the manifold controller relay was unhooked! so it idles smoother and has more torque down low but the stumble is still there.
The spark plugs are new (and gapped correctly), as are the wires (AC Delco), plug well seals, and valve cover seals. The tach doesn't do anything funny except right at startup when it dips a bit, but it does start just fine every time. It was really bad before the AC clutch swap, to the point that I was afraid the engine would die because of it. It was up to almost 2-3 a second.
So I guess my question is, what could be causing this? It's not in the accessory system, I'm 99.9% sure it's not in the spark. I ran a cylinder balance test 3 times in a row, it runs end to end, no test failures. KOEO and KOER both pass 111 with the exception of 521 and 536 (BOO circuit fail, PSPS circuit fail). I doubt either of those would cause said stumbling. That leaves... fuel. (the IAC is new, too.)
If a fuel injector were randomly misfiring, wouldn't the cylinder balance test pick that up? maybe not? How would one go about checking that? Could I maybe look for a dip in fuel pressure during the stumbles? The fuel pump is new as well. Fuel filter was changed recently. I'm just at a loss as to what could be causing this.
If it weren't my wife's car, I wouldn't be worried about it but she won't drive the thing until it gets fixed, which means she's driving my car, which is bad cos I hate driving her car... it's so... stock. ugh. Anyway, any help would be much appreciated. Thank you!
I put a new AC clutch in, figuring the AC pulley bearing was bad. Still does it. Swapped the two idler pulleys with known goods. Still does it. All other pulleys spin freely and queitly. Pulled codes, got a 551 for "IAS" bad. Hey, look at that, the connector on the back of the manifold controller relay was unhooked! so it idles smoother and has more torque down low but the stumble is still there.
The spark plugs are new (and gapped correctly), as are the wires (AC Delco), plug well seals, and valve cover seals. The tach doesn't do anything funny except right at startup when it dips a bit, but it does start just fine every time. It was really bad before the AC clutch swap, to the point that I was afraid the engine would die because of it. It was up to almost 2-3 a second.
So I guess my question is, what could be causing this? It's not in the accessory system, I'm 99.9% sure it's not in the spark. I ran a cylinder balance test 3 times in a row, it runs end to end, no test failures. KOEO and KOER both pass 111 with the exception of 521 and 536 (BOO circuit fail, PSPS circuit fail). I doubt either of those would cause said stumbling. That leaves... fuel. (the IAC is new, too.)
If a fuel injector were randomly misfiring, wouldn't the cylinder balance test pick that up? maybe not? How would one go about checking that? Could I maybe look for a dip in fuel pressure during the stumbles? The fuel pump is new as well. Fuel filter was changed recently. I'm just at a loss as to what could be causing this.
If it weren't my wife's car, I wouldn't be worried about it but she won't drive the thing until it gets fixed, which means she's driving my car, which is bad cos I hate driving her car... it's so... stock. ugh. Anyway, any help would be much appreciated. Thank you!
