After warm-up my truck's idle varies from 800-1100. Often it will go from one of these extremes to the other between red lights. Not only that but sometimes my tachometer will jump.

I don't think this problem has very much to do with the TPS because it only really does it in warmer weather but sometimes when I start my truck up after it's already been warmed-up, like if I stop and run into the store real quick, it will idle at 450-500 but after driving for about a minute it will go back up and be fine. I think this has to do with my cooling system though cause like I said it only does it in warm weather.

Does it sound like my TPS is bad? I've already tried adjusting it twice. Once with an ohmmeter and the other the "quick" way: adjusting it back until the idle drops. Both ways yielded the same result.

 

Engine?
Year?
Model?
codes pulled?
Search.
done any diagnostics yet? (check link in my signature, go to online version, and look at MFI diagnostics for your correct year. Don't just guess and throw parts at it, you will be wasting $ and time!)

 

^ x2

You need to narrow down all of the possibilities before throwing money away. It could be as tedious as tracing down a broken wire to lubing your throttle cable.

Why do you think it is the cooling system? Does it over heat? Did you check for air bubbles in your system? How are the engine grounds?

 

x2 on air bubbles in the cooling system. That can cause the varying engine idle when the engine warms up. Why? When the air pocket hits the engine coolant temp sender, the reading to the ECU drops so it thinks the engine is cold and it bumps up the idle speed and fuel to warm it up. Then the air bubble moves and the temp. sender reads the hotter coolant and the ECU slows down the idle. Park on an uphill grade and open the rad cap and run engine with heater valve open until the t-stat opens to let trapped air out of the system.

 

I'm having similiar problems, lemme know if you find the cause!

 

Sorry I'm a little inept. When you say with the heater valve open do you mean turn the heater on?

 

Yes, heater slider on the dash on hot/red or whatever you want to call it. No need to have the fan/blower running, just need the coolant (and any trapped air) to be running through the heater core and that is what the heater valve being open allows.

 

Okay. Thanks! I'll try that tomorrow.

 

Okay. So I gave it a try this morning. I parked it up on my driveway and took off the radiator cap, started it up, and at first it didn't do anything but then it started to bubble. I just have one quick question. I did it for like a half an hour and it would still bubble intermittently between about thirty seconds. Does it usually take this long?

 

It should take just a few minutes. Were you topping it off as the coolant level went down? Did it seem to help your problem?