Sluggish 1999 Jimmy - gimme some help!!

I have a 1999 GMC Jimmy with approx 140,000 KM. I had a recent tune up and for all intents and purposes, this vehicle runs fine....except..

On initial startup (even when warming up the motor for a minute or so), when I go to depart, the jimmy will OCASSIONALLY be hesitant. It is sparatic and basically won't have any power when pressing on the accelerator. However, if you let go of the gas pedal, and press down again, power often resumes and all seems to be okay (sometimes I need to let go of the gas pedal 2 or 3 times) until you park and re-start. This hesitation normally occurs more in warm weather than cold.

Also, the check engine light will come on periodically. It is, again, sparatic. I can drive 1,100 miles with nothing. Then it will come on 1 week later after 2 miles. It always goes away. I replaced the gas cap, had a tuneup and am stumped. I'm considering changing transmission fluids (I haven't done this yet). I also heard the MAF sensor could be a good start (where is it?). Any other suggestions greatly appreciated. Should I get this code read (does the light have to be on at the time)?

Go get the codes scanned at autozone.

The check engine light is on for a reason.

Go get the codes scanned at autozone.

The check engine light is on for a reason.

If the light resets itself, does the computer keep a memory of all past codes? Or do I have to wait until the light comes back on?

LESTER

I am pretty sure it is your ignition switch, I had the same problem along with some other strange symptoms. The scan may show transmission codes. Make sure you check the ignition switch before getting into any transmission work. It is a common problem with this vehicle.

The ecm stores the codes

If the light resets itself, does the computer keep a memory of all past codes? Or do I have to wait until the light comes back on?

LESTER

Yes, it will store the code in memory.

Thanks for the advice. I went to autozone and had the code read (interesting though, the light was off and the guy said it wouldn't read unless the light was on). Plugged er' in and the problem was......drum roll.....
P0101 - MAF. Bought a new part for $95 and will change out tomorrow. WIll update the success. Thanks all...

Don't ever listen to the AZ counter monkeys.

also, remember to reset the computer after the new MAF is installed.

Reset by pulling the battery cables overnight?

I put in the new sensor without reseting and a new air filter. JIMMY RUNS GREAT!!! Thanks all. Now to get rid of that annoying blinking signal sound....

Reset by pulling the battery cables overnight?

I put in the new sensor without reseting and a new air filter. JIMMY RUNS GREAT!!! Thanks all. Now to get rid of that annoying blinking signal sound....

Yes, reset the computer so that the engine can relearn the proper fuel mixture faster in about 200 miles instead of taking 5000+ to do it on the fly.

Pull the negative battery and the two ECM fuses from the fuse panel if you want it reset in 10 minutes or so.