Vac leak or something else?

[Skaha]

I’ve been going nuts trying to figure out what’s going on, 2002 1500 slt 4.7l. When I’m at idle my rpm surges and falls, I had the same issue about a year ago that I solved by replacing the TP sensor, then just before Christmas we had a cold snap and it started happening again. This time I replaced the Idle Control valve and gave the throttle body a good clean. That seemed to solve the issue again for a short time but we’ve had consistent cold since then and it has started to occur again. Today it’s gotten worse, it’s to the point that when I come to a stop at a red light the rpm dips to a point where it almost stalls and then revs up again. I’ve tried finding a vac leak on the hoses with no luck. Could this be a symptom of a failing brake booster?

 

[Skaha]

In case anyone sees this, I replaced the brake booster which seemed to somewhat alleviate the symptoms so they weren’t as severe. Next I replaced the MAP sensor and cleaned the PCV valve. I drove a few hours over the next 2 days after the MAP sensor and PCV valve work and didn’t experience any idle surges until this afternoon, I drove around doing errands for 30 minutes then popped onto the highway to drive home and since then the surging has come back more severe than before. I’ve actually stalled a couple times when driving very slowly (such as parking). Not sure what to do now!

 

[FaceDeAce]

The 4.7 in one of our other trucks had these exact symptoms. Rather than the parts cannon ... I did some knapkin diagnostics first and when the coffee cup was empty I went straight to work at replacing the EGR valve. Problem was solved. So, perhaps that is the next part to load in the cannon. Try replacing the EGR valve.

Hope that helps!