Hello folks! Would love to get some opinions on an issue I'm currently working on my truck. First off the details:

2006 4.7L V6 Dodge Dakota
150K miles
No substantial repair history (that I'm aware of, bought it recently, CarFax had nothing noteworthy other than regular oil changes)

Month or so ago it seemed to idle low while out driving and stalled once or twice. I did some reading, and a lot of people pointed me to replace the IAC valve and throttle position sensor. I replaced both of these and the issue actually seemed to get worse (or at least happen more frequently). I've also tried to reset the PCM (disconnected positive battery terminal for a few minutes, reconnected, turned key to "ON" not started, waited like 30 seconds, then started). Right now the truck's behavior is it starts fine, and idles fine for about 30-40 seconds at around 800rpm. Then the RPMs slowly drop to around 300, then oscillate between 300 and 200 or so and usually it will then stall.

Any thoughts or suggestions welcome
Thanks in advance!

 

look at the usual suspects, which are air, fuel and spark
how's the air filter? is the TB dirty?, any leaks in the air intake tube? how about the MAP sensor?
do you have good fuel pressure? have you used anything to clean
what's the condition of the coils and spark plugs?

if you press the gas and it stays higher and doesn't stall, then the issue is is most likely not fuel, but most likely something to do with the air. when the TB is closed (like at idle), it's not getting enough or too much and it's causing it to bring the RPM too far down.

by chance have you put it on a scanner to check the air fuel ratio? activation of the open/close loop (if it goes that long)? any pending codes?

 

Thanks a ton for the reply!

Haven't looked at the TB yet, the old IAC valve actually looked alright, but it probably is due a cleaning. I also saw mentions of the MAP sensor, so I've already been thinking to replace that next. Fuel pressure is probably ok as it revs fine and drives great, just has this idle issue. I was going to check out the plugs today but didn't get around to it. Though if there was an issue with them, wouldn't it also manifest when the engine is under load?

I haven't checked the air fuel ratio, I'm guessing that's more than a simple ODB2 scanner can do (I don't think I saw that looking in the menus on it anyway). No pending codes at all.

 

so, if you press on the gas pedal, everything works correctly as expected? so you start, it goes to normal RPMs but goes down to the 2-300 RPM then stalls when just idling?

then keep an eye out for air issues like I previously mentioned, MAP, dirty throttle body, leak, etc...

 

Correct, pressing the gas pedal everything works as expected. I start it, and the odd thing is how it idles perfectly fine for 30 to 40 seconds, a decent chunk of time, then slowly goes down to around 300 RPM then oscillates between 200 to 300 until I sht it off or it stalls.

I'll get the MAP replaced, check the TB and vacuum lines, thanks much!