I have a 2001 3.8L AT with poor acceleration especially when the weather is really hot. It also jerks when shifting when I really press the gas pedal. I replaced the plugs and wires, cleaned the MAF sensor and replaced the idle speed motor. It also drives worse with the AC on. Any suggestions for a cause would be appreciated. Oh ya, the car has 92k mikes on it.

 

That symptom is often caused by a vacuum leak or hose collapsing under vacuum somewhere. When its cool, rubber hoses are stiffer and more resistant to collapse. Any holes in them are also smaller. When it gets hot, the rubber is softer and can collapse in on itself under vacuum. Any holes in them will also expand causing a larger leak. Happy hunting...

 

I checked for a vacuum leak but could not find any. I did change the throttle position sensor though which did help a lot. The car runs 90% better. Wish I could get it to !00%.