After taking a short trip around the corner I came back home and when I put my truck in park the rpms shot up to 3k and stayed there. I jumped out thinking that tapping on the iac and tps would get it to stop but neither did. I eventually just turned the truck off. What couldve caused this?

 

I had similar issues last week.
Mine turned out to be a tps that wasn't adjusted right.

Or a vacuum leak, check your hoses.

 

Agreed sounds like bad throttle position sensor.

 

can the tps on a 4.9l be adjusted?

 

Yea, if i remember correctly it's measuring the voltage coming off of it as you rotate it on the bottom of the throttle body.

Do a search for "TPS" and you should get some hits.

 

Don't forget your throttle cable. I need to lube mine. Sometimes my engine will race if I hit the pedal while not moving and I need to pull up the gas pedal.

 

Aj, you may just need a heavier return spring to close the throttle a bit harder

 

There is no meaningful TPS adjustment. Anything between 0.6 VDC and 1.00 VDC at closed throttle is acceptable. The computer has a compensation algorithm for the closed throttle TPS value. Adjusting it to anything inside that value is an exercise in futility.

If the TPS value is outside those values then replace it. The other key item to look for is a varying closed throttle TPS signal caused by a faulty/noisy TPS. It's a variable resistor that is susceptible to wear over the years.

 

Tapped the pedal at idle just to see it's not a fluke, and, nope, it's not. Might look at it this weekend - kind of a safety concern anyway. Not sure I'd want a stronger return spring, as the pedal feels good as it is.

 

Classic signs of a noisy TPS or a bad connection. I found the TPS connector on my old '92 F350 w/5.8L engine was full of green corrosion. After a cleaning with contact cleaner and a wire brush my intermittent high idle was gone.

 

Connector is very clean. Had it off two weeks ago when I went through many of the connectors under the hood.

TIP: DeoxIT is a great cleaner. Expensive, but by far the best that I have found. Sold at Radio Shack. DeoxIT® D-Series - Contact Cleaner & Rejuvenator