Hey I have a tpi engine that will start up fine and raise rpms until it reaches 1.5k warming up. When it warms up, it stays at those rpms in PARK, Neutral since I have an automatic car. Does anyone know what could be the problem? Would a sensor tell the ecm that its warm already and to lower the rps?

When it is in engaged in drive/reverse, it lowers its rpms to 1.0k.
Also, since the rpms are higher in normal when I shift into drive, the car lunges forward (jumps). I spoke with someone about it before and they told me it could the u-joints need to be tightened. Could he be right?

 

U-joints have NOTHING to do with engine idle.

Check the sticky threads for setting minimum idle air, and tps, and see if that helps, also, check for vacuum leaks.

 

there is a vacuum line running from the left side of the throttle body (as you stand in front of the engine i.e passenger side). Mine was cracked and would do something similar. It would intermittently idle high (more than normal) but then gradually come back down while still in park.