98 f250 problem!

[Lilbigtrk]

my buddies got an 98 f 250 and whenhe started it up the idel was fine then after about 5 min its jumped up and keep going..
he got the truck home but it was doing 30km when he didnt have his foot on the gas....
its a 4.6 V8 auto


any ideas of what might have happened?

[Northern Supercrew]

my buddies got an 98 f 250 and whenhe started it up the idel was fine then after about 5 min its jumped up and keep going..
he got the truck home but it was doing 30km when he didnt have his foot on the gas....
its a 4.6 V8 auto


any ideas of what might have happened?

Dirty throttle body, not allowing the butterfly inside to seat properly or worn butterfly...or maybe the IAC..( idle air control)...my 97 4.6 would get this when it was -40 outside...had to ride the brakes to keep it slowed down.

[taisa899]

intake gasket leak

[swackly]

I would say the throttle body. I clean mine ever spring and fall and it is hard to believe the amount of dirt on it. I also clean my mass air sensor to and never a problem. I would also get a can a seafoam and put it in the gas tank. m2c

[ml878us]

I was helping a buddy do valve cover gaskets on one about a year ago, and it did the same thing on re-assembly.

As soon as it started, it went WOT on its own, even with the butterfly held closed. We (both GM/ Fiero guys at heart) spent an entire evening trying to figure it out, and never did solve it. ......

BUT, common sense says that an engine acting like that is taking in false air SOMEWHERE, so I would go the routine we did...check all the vacuum hoses, intake gaskets, butterfly seats ect, ect, ect (and mechanical linkages as well)---then take it to a dealer and throw money at it until it runs right again.:icon_razz:

[BIGPHIL]

might just have a bad iac.......or a tps... check the volts/omhs