i have a 1988 jeep comanche and when i stars it up the engion races and i dont know why?

[Aaron M]

i just bought a 1988 jeep comanche and when i start it up the engine races to the point of where i have to turn if off. the pistons and everything were just replaced recently. so if you can help me it would be greatly appreciated.

 

[phosizzle]

Check to see if the throttle body is stuck in the open position. You may just need to clean it with a throttle spray cleaner.

 

[jimmy]

If the throttle isn't stuck open (as mentioned above), check the TPS or throttle position sensor. It is a sensor on the throttle body that monitors how open the throttle is, and adjusts ignition timing and fuel timing. In short, when the TPS fails, one symptom is a high RPM idle at start up. I'd know, because my brother has an '89 Cherokee with a bad TPS, and the idle is around 2,500 RPM at startup, but he doesn't seem to mind... Spend the $50 and replace it, it will be worth it.