Did you look through all the repair records for the car to see if there have been any replacements of the LIM gaskets or the UIM?
Regarding the cold air, search this forum for "airmix acuator" or just "acuator" and you may find some help. All check out www.*********************.com and search there also. You've come to the right places for help.

None of the lower intake manifold or upper intake manifold gaskets have been replaced during his owning the vehicle. I am planning on doing this myself after winter. Is there an easy way to check for a leak besides taking off the UIM or checking the oil or exhaust for coolant?

Thanks,
Nick

A poorly running vehicle is a good sign of it, but it'* never too soon. I changed my IM gaskets at 150K miles and found that they were almost to the point of failure. You don't know until it strikes!

I took a video of the bogging down that I'm getting. The vehicle was in park, warmed up fully with no check engine lights. I used my OBD-II USB scanner with ScanXL and it turned up no "hidden" check engine faults.

If I slowly accelerate the engine to, perhaps 4000, there'* no problem. If I step on the gas abruptly, I get a stumble from the engine (as you hopefully can hear in the video).

With the transmission shudder, If I keep my RPMs below 2000 or so, I can prevent the shudder from happening, but even in 2nd gear, The car will shudder under heavy throttle. It seems like temperature has an impact on this. I just drove the car after it was sitting here (about 40 degrees) for a few hours. I took off right away and even under full throttle, I didn't get any hesitation.

I filled up with 89 octane and threw in a bottle of fuel injector cleaner for good measure. I'm thinking this is an ignition problem or sensor (perhaps MAP, TPS, or MAF?) Using ScanXL and getting the GM PCM data stream, the TPS was giving various readings from negative degrees to about 30 degrees, all when the car was idling. I can post some of the data if that would help...

Any ideas?
Nick

Try unplugging the MAF and see if that helps. Had a car here a while back that acted a bit like that and it turned out being the MAF. The engine will stumble a bit at first when you unplug the MAF. But should settle down.

And I've read a TSB in AllData about an oily MAF causing erratic or harsh shifting because of over-oiled aftermarket filters. While I don't think the PO ever used an aftermarket performace air filter, the MAF might be dirty or bad... I'll check that and post back.

Thanks

Unplugging the MAF didn't affect anything; the engine ran worse. I plugged in my ELM327 and the voltage for the MAP is good. The IAT and Coolant Temp Sensor are both good. TPS and MAF are kinda hard to interpret (their readings were jumping around too much). I'll be cleaning the MAF anyway as soon as I get the proper security torx bit.

One thing I did notice was that my bank 3 long term fuel trim averaged out at -12%. My long term on bank 1 was about +3%. These averages were after the car was idling for 15 minutes.

I pulled the front 3 plugs and checked them. They were all in good shape, regapped them (they were at about .063") and lightly cleaned them with emery cloth. I checked the coils and the secondaries were fine. Didn't check the primaries.

I checked the fuel pressure... It'* fine and within AllData'* specs. I am getting a fuel smell from the passenger rear of the car, around the fuel filter area...

I'm going to hook up the scan tool again and see if it will tell me the transmission line pressure. I can get all of the GM PIDs, so I don't see why not. I'm thinking it might possibly be a sticking pressure control solenoid??? I haven't gotten a P1811 code, so I'm not sure...

Any ideas?
Nick