I have the 3.9l engine and it started what I call loping at idle and continues while driving. When I get up to around 25 MPH during acceleration the engine RPM goes to around 2000 quite rapidly then will accelerate. I've changed the EGR and had to repair the EGR tube since the one I ordered did not fit, PCV okay, equal compression, can't find a vacuum leak, and tried different plugs. Any suggestions appreciated.

 

Check the throttle position sensor. I was able to identify this on my truck with a Bluetooth scan tool. The throttle sensor tells the computer the position of the throttle. If it isn't accurate, fuel is injected at the wrong amount, causing rich or lean conditions, while trying to correct it's self (lope or surging idle)

 

What kind of shape is the plenum gasket it? It's a non-visible vacuum leak.

Loping at idle like that is usually a vacuum leak as the ECU tries to adjust enough fuel into the mix, nope, too fast, lean it down, nope, too lean, enrich, nope, too fast, lean it, nope, too lean ... ad infinitum et nauseum.

This is especially telling if it doesn't lope when first started, but does after 60 seconds or so.

RwP

 

Feeling dumb after all these years! 4 and 6 wires reversed.

 

At least it was easy. (once you found it.... )