Truck starts but idles poorly before stalling.
with maf unplugged the truck will idle rough but will stay on.
I have checked for vacuum leaks but can’t find any
any ideas?

 

Have you checked for any codes ? A rough idle can come from many things. Best to scan the engine and sensors to diagnose possible problem source.

What sensors/problems can cause rough idle?

• Vacuum leak.
• Fuel pump issues.
• MAF (Mass Air Flow) sensor.
• ECT (Engine Coolant Temperature) sensor.
• IAC (Idle Air Control) valve.
• TPS (Throttle Position Sensor) sensor.
• Throttle valve. etc.

If you don't have any type of scanning / diagnostic tools then then will need to go into a shop and have it done.

Don't start throwing parts at it.

 

Unfortunately there are no codes. Codes were cleared by previous owner.

 

I literally just went through this earlier this week and fixed it yesterday. Is the 2nf MAF plugged in? There are two. One on top of the intake tube that you can see and one on the bottom.

 

it is plugged in! But there is a chance that it has gone bad . Do you have a link or part number incase that sensor does have to be replaced?

 

Have you tried cleaning them? Use MAF cleaner $9 but it is a simple process. Spray not too close and let dry for 30 minutes.

 

There is only one MAF. It sits right behind the air filter housing.

There is an Intake Air Temp sensor that goes into the ducting and the Idle Air Control valve sitting at the throttle body end...that’s for sure.

 

I’d pull plugs and see what they show you.

These 4.2s take a lot to trip a CEL for misfires. Once I get this boot off my left foot, I’m pulling plugs to hopefully rid myself of this rough idle. Had the same issue about five years ago. It’s been burning oil since then. Plugs were caked with brown stuff—burnt oil.

What is your idle speed if you have a tach? Mine is steady around 800 RPMs, back then, it may have dipped a couple hundred RPMs lower at times.