need help rpms keep going up and down when in park

[sgalka91]

like the title says everytime i start my truck it will will idle up to about 1500 rpm then go down to about 300 rpm and it will keep doing this until i put it into either drive or reverse then. it is fine for the most part when in drive or reverse. but evertime it is in park it will idle up and down. anyone know what it is?

 

[Yellowsplash]

Sounds like the Idle Air Control (IAC). Carbon buildup can cause this. Remove it and clean some of the carbon out of it. This will not only allow more air to circulate through it, but also allow the motor its full range of motion. I would also spray the ports in the intake manifold too.

 

[sgalka91]

i took the IAC off and sprayed it clean. But that didn't fix the problem. Anything else it could be

 

[beejium]

did it just start happening since the cold? iac is the first to come to my mind as well, but i was thinking maybe vac leak or intake temp sensor. ... no codes? no engine light?

 

[redneck_rainey]

i have a 01 4x4 4.0 with the same problem. just a real hard/ rough idle. i have had two incidents where as im taking my foot off the brajke in drive it dies.

 

[sgalka91]

no check engine light. and i dont really head a vac leak.

 

[beejium]

when was your last tune up? i mean heck mine only acts up when the egr controller vacuum hose blows off, which causes the engine light to come on as well as idle really funky. it also causes random loss/gain of power. maybe the bulb has blown in your dash... mine was. with such little info we can only speculate. see if there is any stored data. test for leaks the old fashion way, spray some soapy water around the hoses and such. if idle changes, or you see bubbles there is a leak. don't go by ear, you won't hear leaks past the cooling fan.

 

[odie1969]

kinda dumb question but is it cycling? and are you running your defrost, In my truck I notice when the defrost is going the rpm with will increase and drop as the A/C compress cycles.

 

[sgalka91]

it does it when the a/c is on and off. Does a fuel filter seem plausible?

 

[beejium]

only $10.... change it, then you will know it's not the fuel filter.

 

[Turboedranger]

Egr?

 

[redneck_rainey]

any other help for us you guys?
any is appreciated