LIM aftermath

[JimSchmidt]

Hi guys (and gals)!
I have a 2000 Alero and I did the infamous LIM job. Replaced using the aluminum Felpro gasket kit. Once the PCM recalibrated, the engine goes into a pulsing cycle (only when idling and warm) from near stall to about 1500 rpms. Reset the PCM, ran great for about 4 minutes then started the same pulsing cycle. Exhaust smells like incomplete combustion. no smoke of any sort from the tailpipe. On the highway car otherwise seems normal except transmission shifting seems hesitant or confused. Come to a stop sign and you can feel it trying to pulse a bit if its really warmed up. Also, immediately after the job it seemed to have more pep than originally.
It seems to be a PCM thing for sure, and no other hoses/electrical are out of place hat I can find. No damage was done to any of them etc. and no coolant was or is in the fuel system. No oil has ever gotten into the coolant either. Should note it's a 3.4L engine as well.
Have been told to test the cat by drilling a hole before the cat to see if idle will smoothen out.
I'm about to do the drill testhole , but I'm skeptical about the outcome after having re-read your explanation, for these reasons:
Until the car comes up to about half opperating temperature, it idles fine. It's definately mixing rich, even when cold and while the intake air is cold, it runs not so badly. when at a red light its still fine @1100rpm +- unless very warm where you can feeel subtle pulsing. midrange power when warm, is down a bit but when you hit the pedal after a little bit of slugishness it gets up and scats. Not likely %100 but no sweat passing those who like to make passing a problem. The pulsing is very consistant and pretty much completely predictable. It definately feels like it's controled (PCM) somehow. Also have noticed that the fuel economy has taken quite a nose dive, overall and the exhaust is smelly all the time. Definately smells rich. The power loss, is also consistant throughout the entire power spectrum, and I'd have to guess that its down about %20. Before the LIM job none of these things were an issue, and the coolant was not getting into the exhaust, but only leaking externally. My mind goes to the O2 sensor, but why would that change? during a LIM job? Could see if I had to disconnect (and forget to reconnect) it but quite sure I'd have one nowhere near that?? Thinking I'm going to have to get the PCM scanned and pray that it gives a good idea where the problem is.

Above I said "little bit of slugishness", by that I should say, it doesn't misfire or even seem to. Its just a little slower to come up to speed than normal. No significant "roughness" in the motor, just not quite what should be there, which holds true across the full gamut of RPM range.

Also.. Don't forget the pulsing started immediately after the job (first day driving) yet the power dip didn't untill the wifes battery light excursion.

Any ideas??
This cant possibly be a first?!?!

TIA for anything you can give me to help!!

[skeeter123]

So your temp gauge is working? I was thinking it could be the ECT temp sensor/wiring, but if your gauge is working that's probably not it. I also think that the IAT temp sensor can cause problems with fuel mixture and transmission operation. The wires from the IAT have been known to go bad. If you can borrow a scanner that shows "live data", you could monitor the reported ECT and IAT measurements.
Hope this helps.

[JimSchmidt]

Thanks for the reply.
Temp gague is working fine. Borrowing a reader isnt likely, I'll have to foot the bill for the readout..
ECT was replaced a few days before the LIM job.
FWIW, when I disconnect the IAT it settles some but still pulses while disconnected

[BNaylor]

How's the engine vacuum? Have you tested it with an automotive vacuum tester? It could be a vaccum leak.

And welcome to AF.

[JimSchmidt]

Problem solved!!!!
For any who may encounter this again and make the same mistake I did, It turns out I somehow managed to pinch a wire (purple) from the O2 sensor on one of the coilpack mounting nuts. fixed it, reprogrammed the PCM and problem is solved. Thanks to all who put forth the effort to post!!!

Thanks for the welcome!!