Sluggish Acceleration and other problems

I've had my 04 Envoy for about 6 months now. It has 72,000 miles on it. Since we have had it, when accelarating it is slow/sluggish until you basicly put the petal to the floor. I was wondering if this could be the throttle position. I would like to know how to reset the throttle position learning and also reset the ECU to learn my style of driving. My MPG is horrible right now sitting at about 16 city. Yesterday the dreaded "service engine soon" light came on and hasnt went off since. I plan on stopping by Autozone on the way home from work to get a code and will post back later tomorrow. I know that my oil needs to be changed, would it come on for that even though it has a "change oil" light? Any help in the matter would be greatly appreciated. Im suspecting an O2 sensor for the service light. If any more info is needed please let me know. Thanks again.

Welcome to AF, no one is getting much better than 16 city assuming this is 4wd. Disconnect the battery for a restart on the relearn, keep in mind there have been several software updates to your pcm, some affect idle quality and shift firmness.. First get the code and post back. PS don't disconnect the battery until you get the code and post back, as I said.

Thanks for the quick reply and the welcome. My Envoy is 2wd. I would assume that the MPG would be in the range of 18-21 but not sure, havent looked that up so much. I do plan on taking the rack off and whatever else that I can do to try to remedy that as far as full synthetic oils and such. I will get the code and get back with ya. I dont get off work till late and will try to make it to AZ before they close, if not then on my way back to work I will get the code and post back.

I have tried the gas cap deal with no avail. It runs just like it did when I bought it six months ago.

As far as the PCM updates, are you saying that they have already may have been done or that I should try to go get it done? I assume that this would be a dealer thing and what would be an estimated guess on cost?

Get back with ya later.

Also, if I do the thing where you press the gas pedal to the floor 3 times with the key on but not running, would that make the code disappear as well or would it still be stored?

Just wanted to see if it comes back or not. I guess the best thing would be to just go get the code before anyting.

What's the code?

Ok, went to the auto parts store. The code is P0442 - Evaporative Emission (EVAP) System Small Leak Detected. The guy told me either their is a vaccume line that may have a small leak or that the gas cap seal may be bad. I havent actually tried the cap. I just took it off and put it back on. But my thing is, I havent put gas in it for about a week so could it just go bad even after it has been screwed on for a while.

In any case, would love to hear your guys' thoughts.

If the cap is not loose or leaking then the diagnosis is more difficult, unless an obvious problem is seen such as a rusted or leaking hose in the evap system, it will have to be put on a smoke machine to detect the source of the leak. It will not affect driveability unless there is a gross fuel leak somewhere. The depressing the gas pedal has no affect on the codes either way. Only a scanner will clear them.

Well, I looked at the gas cap and the seal is looking pretty sad. I will go get another and see if that works. Now, when I get the new cap and say that it was the problem would the "service" light go off on its own or would I still need to get it cleared? Also, when I disconnect the battery to clear the PCM would that also get rid of the service light till it finds another problem?

Don't dsiconnect the battery, if the problem is solved, the next time the pcm commands an evap test and the system passes, the lite will go off.