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 when 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.

 

You might wanna give the plugs and wires a quick check, make sure none of them have vibrated loose.