Bandit76

My 92 Firebird recently developed an engine problem. It started with the idle being very jumpy (down to 500 rpm then it would leap up to about 1800 and back again), but with good throttle response. It would cough out a lot of black smoke on hard acceleration though. It gave me a code 44 (lean).

I replaced the IAC sensor and the idle got lots better, but it still smoked badly. The O2 sensor was also replaced, and my mechanic found a small vacuum leak.

Friday night it was given a major tune-up (plugs, wires, Accel cap/rotor, pcv valve, fuel filter) and was driving great, up until last night where it started to have an occasional miss and rough idle.

Any ideas? It hasn't flashed the SES light after the vacuum leak repair/O2 sensor replacement. Could the MAP sensor have something to do with it?

Thanks for any help.

scoob8000

double check timing (ive adjusted it before and had the holddown clamp come loose), and double check for vac leaks..

TomP

I like Scoob's idea of checking the timing (part of a major tuneup, by the way). The TPS might be out of adjustment, too- er, wait, unless it's the non-adjustable type.


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

Bandit76

I didn't get to the timing 'cause it was already midnight by the time we were done putting in the new parts.

I've never touched it though, and the distributor was on tight. But I will check it since I was planning to anyway.

Jester checked out the TPS sensor, it came out looking ok.

Please keep it coming, guys, you're helping me narrow down the problem

TomP

It could be the MAP sensor.. is that the same test as for a MAF sensor? With MAF cars, you can disconnect the sensor (which throws a code), and drive around. If the car stops acting up, that means the MAF sensor's bad.

I don't know if that's the same deal for MAP, though.


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

scoob8000

hrmm did you set the IAC when you put it in? i forget the proceedure, but its in the shop manual.. i think you just put the key in run position, give it about 1/3 throttle, and start it let it idle that fast for like 10 seconds and turn it off without moving your foot.. something along those lines i think..

Bandit76

The crappy Haynes manual said nothing about resetting the sensor, but thankfully the instructions that came with it mentioned something. It said to drive the car at 40 MPH to make the idle go back to normal, and I did.

I'm suspecting the MAP sensor too, I'm not sure how to test it. I'll look in the book. Otherwise I'll just stick a new one in there, won't hurt either way.

Nick_biggity

dude i have the same problem in my 3.1 I try checking the fuel pressure reg. thats what mine was the vac hose was disconected.

Bandit76

Thanks, I'll have to check that. I'll go over all the plugs too, check that none came loose.

Gabriel

scoob8000

map? or your maf.. two ways to test a MAF, one, while idling tap the unit with the handle of a screwdriver, if it engine stumbles is prolly bad.. the other way, unplug it and start the car, youll get a light, but if the problem goes away there ya go.. as far as the map goes.. i forget, i just remember there being a test you gotta perform with a multimeter..