Engine wont pick a RPM when in park.

[DR3W]

My 2000 4.6L keeps reving between 300-1000 rpm when in park. Idk why, only in park. Not at a stop sign while driving though. Any ideas? Thanks





2000 xlt 4.6L
4x2 170k miles

 

[99 Expy]

Is it a constant change in RPM, or does it change every little bit, because it is normal to change rpms every once in a while. and does it do it while cold and warm?

 

[panda24619]

check the elbow in the back. if you never changed it it could be that. i had that issue when the elbow went bad.

 

[seeker]

Revving up and down is a sign of a vaccum leak.