low to fast ilde (F.I.)

Ok so here's the scoop on whats wrong. I recently did my thermostat and shortly after I will start my truck and it will idle normally but then it just starts to climb higher and higher slowly until there somewhat of a cutoff then it drops very fast and goes right back up. It keeps going high and dropping within a few seconds. I also notice that when it does that there's no heat until it it finally goes back to normal. I have a bad feeling it's the water pump but i've never heard of this happening before. Or it's something computer related.

If anyone has any insight on this please do help out as this is my only daily .

Thanks,

Dale

I think the idle speed on FI trucks is driven to some extent by a temp. sensor on the block.If it is faulty, it would cause the up and down idle.There are 2 sensors for temp,1 for the gauge nd 1 for the computer.Water pump may be bad as well but when they go bad they usually leak out the front of the truck.Only way I know how to test is leave rad cap off,start truck,let it reach op temp and see if u can see H2O circulating or leave cap on,warm truck up and see if u can feel water circulaing thru upper rad hose.BJ

TPS you can get one at your local parts store for like $20

Thanks guys i'll try that out. Where is it on the block exactly?

Dale

TPS (Throttle Position Sensor) is mounted to the throttle body. Should be fairly easy to access.