Info on the truck: 2003 regular cab, 4.2, 5 speed manual transmission

So recently my truck has been idling badly. It's most noticeable when I turn it on to let it warm up after work and its been idling for several minutes.

I know v6s don't like to idle smoothly, but there is a noticeable vibration that comes and goes, and occasionally the rpms will drop to ~400 rpm, almost die, then jump back up, drop again and even out. But it only tries to die every few days.



In addition I've noticed that when I let the truck roll in neutral (such as to a stop light) the rpms will stay around 1100-1500, then drop to 700-900 when I come to a full stop.

There is no check engine light but I scanned for codes and got p0171 and p0174.

I've been suspecting the IACV is the problem, so I'm going to clean it this weekend. In addition I've changed the spark plugs, wires, coilpack and cleaned the MAF.

Has anyone else had this issue? What fixed it for you?

 

Probably an intake manifold gasket. Check your pcv hoses and elbows first though

 

Will do. I sprayed some starting fluid around the gaskets and didnt see a jump in rpms

 

Update- Removed IAC and cleaned it. It was actually really clean already. cleaned the throttle body, TPS connectors and the MAF. Still idles rough (But I havent heard it try to die recently!).
So any other suggestions? Thinking maybe fuel filter? I've heard the PCV valve is troublesome. Also a pain in the *** to get to lol.

 

The 4.2L had issues with intake gaskets and isolator bolts leaking. Chances are that's your issue.

Wayne

 

Pcv valve is very easy to get to

 

Funny, you mention this. Just bought a 99 with same engine and manual transmission. I will be going through it this weekend but I have the same issues.

Big Fish

 

I've already tested the intake gaskets by spraying starting fluid at them. If the RPMs jump it means there's a leak, right? Mine stayed consistent.


I guess I'll tackle it this weekend if it stops flooding LOL.

 

Starter fluid is a "trick" to possibly find a vacuum leak but shouldn't be used to rule it out completely. I have done two intake gasket replacements. One on a 4.2 and one on a Escape and neither revved when trying starter fluid but in the end the problem was the intake gaskets.

Wayne

 

Thanks. I guess i'll keep that in mind, and replace a few other common causes before taking the intake off. Any tests you know of to sure fire diagnose if the intake gasket is bad?