Vehicle:
2001 F150 XLT 4.2 V6

Symptom/s:
I have an irregular vacuum leak (I think). Temperature hot or cold it will stall or attempt to stall. When I notice it, I can turn off the A/C and put it in neutral and accelerate and it seems to seal itself off, then it will idle fine. I have had it not want to start completely, so then I put it in neutral start it, it hesitates and wants to die, I then put it in drive and it seals itself and runs great.
I have replaced the intake seals, EGR valve, PCV valve.
What confuses me is the inconsistency, I am not able to find a pattern to diagnose.
I am hoping that someone might ask the right question or have the right suggestion.
Thank you for your time.

 

I think you may need to clean or replace the IAC.

 

I feel like I am replacing a vacuum hose every other month nowadays. A bit off topic, but this started off as thinking it was vacuum due to past issues and rough idling. Not sure if it was the cold weather (in Florida), the deteriorating hose or just the coil, but my truck developed a convulsive cough on my way in to church on Sunday. Come to find out, after going down the rabbit hole of other smaller issues, it ended up being a bad #2 ignition coil that wasn't giving an error code - and was very sporadic.

 

The 4.2 V6 only has one coil pack.

 

https://www.f150online.com/forums/v6...apologies.html

See if this helps....