i have a 2002 4.7 and when the motor trys to idle down it runs at about 1000 rmp it then feels like the trans is engaged and just wants go. and when you start it or put it in park it revs up over 1000 and wont come down tell i put it in park. i think it could vac leak and my parts guy said that same. i was looking and can't find anything yet. any ideas or has anyone had the same problem.

 

If you put it in park the engine idles down correctly? (650 rpm or so?) If so, it's NOT a vacuum leak.

If you wrote that wrong, then the engine will be idleing high all of the time UNTIL you put it in drive. At that point it'll slow down some (foot on brake) but when driving it's like your on cruise control at 30mph all of the time.

Things to check:
Throttle Position Sensor (TPS) - dirty or stuck / non functioning.

Vacuum leak - check the hoses coming from the drivers side of the throttle body, especially the larger one on top. It's prone to cracking right where it bends coming off the throttle body.

Brake booster vacuum line.
PCV valve / lines at the front of the passenger side valve cover - the PCV will crack if the line is pulled on.

There's also a pressure sensor on your power steering high pressure line that cuts into the idle circuit somewhere (controlled by the PCM) so make sure it's not broken.

I'm sure that it's tied in to the tranny somewhere as well.

Hope this helps.

Bob

 

Sounds like an IAC to me.

Clean the Throttle body. Take it off and clean it really good with Throttle Body cleaner (about 2 cans) and an old tooth brush. You can try to clean up your old IAC and see if it fixs the issue or not. If not I would replace the IAC. Reset the PCM and enjoy that new truck feeling.

 

i agree im leaning towards a bad IAC motor

 

yea when i put it in driver it drops put it wants to driver with brake on in drive ill look at the iac and clean the body.

thanks for the help

 

I think the boy is speakin' English but I just can't understand him!

Bob

 

LOL........Hard to understand I agree.

 

ok let's go over this one more time. when i start the truck the revs up to 1000, 1200 rmp and stays there when i put it drive the rmps drop 700 rmp or so. then when i come to a stop (stop light) after driving the motor revs up and down 600 to 1200 rmp tell i let of the brake and start driving again. but when stopped (stop light) the truck trys to over drive the bakes but only when the motor revs up and down.

but then all of the enplaned just comes and go's by start up and shut down and day by day.

that help

 

Have you done what Hydrashocker said

 

Thank you, that makes it easier to understand!

Given that the problem comes and goes, it's probably *not* a vacuum leak. +1 on the cleaning of the throttle body and clean / replace the IAC.

Bob