i was stopped at a light today with my foot on the brake and my engine would basically rev itself and try to launch forward. thinking i was going to hit some one, i went to go shut if off but it beat me to it and shut itself off...in the middle of the road. when i turned the key over, i wasnt getting anything. i waited for 5 minutes and it fired back up but was still chugging forward. the truck is completely fine while driving...just when it gets down to idle, it tries to give gas to itself i guess? its also super fast when you just take your foot off the gas and let it go itself.
heres what a former mechanic came up with for me- the head gasket is leaking. that could be the cause? the engine obviously isnt running on all cylinders and is running very rough. he also said it could be a computer problem...i disconnected the battery and let it sit for 15 min but that didnt change anything. any one have ANY idea whats going on? im about to drive this thing off a cliff :/

 

i'd be willin to bet on a cpu problem. but i wouldnt rule out the head gasket either. weve got a f350 7.3l (not even close to the same i know but still) it was having problems with shuttin itself off when comin up to lights or whenever you let off the gas down to idle. two new batterys and aint had the problem since.

 

hmm you ever have problems with it launching forward on ya?

 

does the front of your truck happen to have one of these on it?








All joking aside, it sounds like it may be an issue with the idle air control system, or a vacuum leak

 

sounds to me like its got a vacuum leak. what engine do you have? it was pretty common for the v8's to have vacuum leaks at the intake manifold/plenum gaskets. how many miles on the truck? and is the head gasket blown externally? or internally?

 

Sounds like a common vacuum leak...I had the same thing happening to me just a week ago....

 

a vaccume leak? hmm well how would i be sure about that? today, it stalled out 3 times in my driveway. id start it up, the headlights would dim, and then itd just die....then it was completely fine for the 20 minute drive i went on...i avoided idleing just in case. but other that that...A okay

matt, 152k miles on the 5.0l engine- and im not sure on the gasket. its leaking, thats about all i know. my mechanic told me this.

 

sounds like a sticky IAC(idle air controll valve)high idle and low idle(stalling)are both very common symptoms.

 

IMO the best method is with a smoke machine. simply pushes smoke in the intake and comes out wherever its leaking. but i'm sure you wanna try solving it yourself? you could try spraying carb cleaner around the intake. if it changes the way it runs then its leaking wherever you sprayed. i'm not a fan of the carb cleaner method due to melting plastic but it does work. you could even visually look at your vacuum lines and hoses for an obvious problem.

 

yeah, lets hope its a line/hose. but im sure it could be a deeper problem then just hoses and lines, correct? so if i find no leaks on the hoses/lines...what next?

 

what paralyzer and patman suggested. Check the Idle Air Control. Pull it off and inspect it

http://www.muscularmustangs.com/iac.php

When it revs up its going to want to take off on its own, when it drops down low its going to stall. Will also make it run horribly

Any other signs of a bad head gasket? Coolant loss, oil coolant mixed, missfires, over pressurized coolant... etc?

If not, check the IAC

You should be so fortunate how easily accessible it is. My 99 2v 5.4L is a knuckle buster

 

You've already got several IACV and I'll add my name to that list. I wouldn't rule out the throttle body needing cleaning but they're close to in the same area I believe. Vacuum leak is definite possibility.

 

the cause of the rough idle and stalling actually turned out to be the airflow sensor. i reset it and all was fine.

toyz- yes i have oil and coolant mixed, loss of coolant, all that jazz. no misfires, but the gasket is definitely blown