Ok so im a newbie on this site with rookie knowledge to this truck. i have fixed a few things but this one problem has me scratching my head. so when i start my truck it runs fine after a few minutes and time to warm up it starts to rev up and down really high. when i step on the break it idles down but continues to rev up and down. i checked all the vaccum hoses and the air box seems fine...so im not sure what the problem could be i was thinking maybe the Mas Air Flow could be the issue...anyone having a similar problem or know what it could be?

 

The idle is set to high and the TPS is either out of adjustment or bad.

 

what he said. i had the same problem and it was my tps. it kinda came loose and fell off while driving. trust me fix it now. it not fun to have it towed home.

 

So i checked the TPS today and it was working fine it that was not the problem however i forgot to mention that my truck has been running cold all the time...so now im leaning towards this being a coolant temp sensor....what do u guys think??

 

check coolant temp sensor and coolant level possible t-stat stuck open

 

Truck is seeking idle and can't really find it. Does it have codes? Seems to lean toward tps and or airflow. check for vac leaks. You said your idle goes down when you brake, thats a vac leak in your line going to the booster and or your booster is bad.

 

Yeah good call kiroshu I forgot about the first thread stating the change when the brakes were applied.