I know it's not 3rd gen related, but I don't know where else to go right now. I just did a TBI swap on my Monte Carlo, and fired it up for the first time. It runs okay, but the "Service Engine" light is on. I installed my code checker tool, and the light constantly flashes (no pausing at all). Did something get hooked up wrong, or is this a different kind of code that I'm not aware of?

 

If you jumper pin a&b with the engine running it will show cross counts. Fast flashing = probling for O2 sensor voltage, in other words it's in open loop. If it flashed every couple of secs, that's a cross count. AF crosses stoichiometric, lambda =1 (14.7:1) and it's in closed loop.

To read codes, turn ign on but engine off.

 

Thanks, that explains why the light went out after the car ran for a few minutes. Now the only thing I can't figure out why the idle won't steady out. It randomly goes from ~600 RPM all the way up to 950, and then back down again. I'm thinking maybe it's a vacuum leak? I replaced all the vacuum lines, so I know that it's not because of old, cracked rubber.

 

And of course, when I get home and try to get the car running, it won't start. I have spark, and the injectors are firing...so why won't it run? I'm definitely confused now!