it only happens once when I first start up then its ok and no check engine light. is there a way to diagnose the problem?
When mine died, no check engine light came on. It was so bad that I had to get it towed to the shop. They didn't think anything was wrong with it because of the no check engine light and they had gotten it started fine (with a little bit of gas pedal action). They had to call me to ask me what the heck it was doing. They figured it could be the TPS (not sure if they tested it or anything) so they pulled it. It was pretty melted. Apparently it's very easy to pull. They replaced it for free for me for that reason. I'm sure you could check it yourself, you'll know if it's going on you or not by looking at it unless it's an internal defect.
I started noticing it when I ran the 1/4 mi. at Wharton and was having a really hard time getting the Jeep to go. Once I was out of the mud it was fine so I didn't really think much of it. The Jeep made it all the way home and on a few other trips. I parked it over night (by then I realized it was having some issues) and that was that, had to call the tow truck the next morning.