Pulled my Dakota out of storage today and left it idling while I locked the place up again. Was idling fine when suddenly there was a VERY loud 'POP' and the idle dropped, shot way up then dropped again and stalled.

Checked for obvious signs, didn't see anything out of place.

Truck starts right back up as long as your foot is on the gas. Take your foot off or just let the RPMS drop a little, and it cuts off. Not spit/sputter die, just OFF.

Didn't have tools with me at that moment, so I'm going back tomorrow to take a closer look.

Any suggestions on what to check?

On a side note, truck sees limited use lately, and it hadn't been run in about a week. At that time, there were no issues.

Thanks.

I don't know anything about the first part of your post, but this part sounds a bit like IAC motor troubles.

Had a '90 Dakota v6 did something similar; was IAC.

Sounds like a big vacuum leak. Could be the IAC but could also be some other sort of vacuum leak. PCV, PCV hose, brake booster hose, rubber caps or plugs on the intake, etc.

That has a barrel intake like the 5.2 right? Those have a metal plate bolted to the bottom of the intake.(at least the v8 intakes do) That gasket can blow out causing a big vacuum leak. Usually the tell tale sign is a really high idle and a lot of pinging on the road.

Another IAC vote. this happened to me as well. If I remember correctly, I did shoot some carb/FI cleaner in it. Settled it down some

I'm thinking IAC as well. What threw me was the POP it made. Backfire? I don't know where it came from as my back was turned when it happened.. I wasn't able to get back to the truck tonite, but I have a spare IAC that I can try tomorrow.

I checked all the vacuum lines and capped ports and didn't find anything. I did the plenum upgrade shortly after I bought the truck, hopefully that didn't go bad again.

I'll report my findings tomorrow.

I would drive it and get it fully warmed up before doing anything. Its possible that you had a low voltage spike when starting and the computers memory is erased. Once it relearns it may be ok.

Hold the throttle at a high enough speed to stay running the next very slowly lower engine speed so the PCM can learn the IAC steps to regain control.

x4 for idle air control.

You can take it out and clean it with oven cleaner first. That always works for Me along with O2 sensors. I just did one and took the whole throttle body off, brushed it good with gas and compressed air to blast the crud out.

Runs like new.

A majority of the problem was the IAC......

However, I found two other issues?

1) The throttle body baseplate gasket was in two pieces. And based on witness marks on the manifold, it had been that way for some time. I replaced that gasket when I did the intake manifold, throttle body hasn't been off since then until today. Source of a vacuum leak?

2) the port that the MAP (?) plugs into was almost completely blocked. No amount of spray or compressed air was clearing it, I had to get after it with a metal pick. Carbon? Dirt? I could have missed this the first go around.

I didn't replace the IAC, I just gave it a good cleaning and polish. Turned out my extra IAC was different, so I couldn't use it.

Truck idles MUCH smoother now and smells different now too, leaner? If that makes sense. Gave it a 5 mile run, she does pull harder when matted now (cup holder on dash slid open..... )

I spent so much time tinkering on it, I never did get to work on the roof. Oh well. I actually enjoyed doing this today. The weather was good, no interruptions, just got lost in it for a few hours. It felt good.

Thanks everyone!

All was great for a few days, then the problem came back, but with a twist? Between work and nursing a bum ankle, haven't really looked into again until this past week.

I went ahead and changed the IAC and the fuel filter. Truck runs buttery smooth now!

BUT...as the truck warms up, the idle gets lower and lower until it reaches full temp where it won't idle at all. Doesn't matter if you're just sitting idling or driving, take your foot off the gas and it just dies.

I switched the IAC because it wouldn't idle cold or hot, now with the new one, it idles only when cold.

It doesn't run rough at any point, it stays smooth at all times, even just before stalling.

Bad IAC?

Any vehicle I've owned with a vacuum leak, the idle went higher, not lower, but I checked everything visible that I could and didn't find anything.

Suggestions? I REALLY need this truck right now, but its basically undrivable.

If you know someone with a snap on or simular scanner have all the settings reset to default.

Is that even possible with OBD1?

Along those lines, I did disconnect the battery while I made the change, thinking it would 'learn' the new IAC?

For a temp fix, you can unplug the speed plunger and turn it to an rpm range that works for you, then leave it unplugged. Its a compromise between a too low rpm cold idle and a too fast warm idle. I choose the correct warm idle and do a slight power break when its cold, until it will idle on its own.

My temp fix is about 3 years old now, my truck is a rusty pile. Its probably the best its ever going to get because it only see about 3,000 miles a year. I've been hoping I only have to drive it 1 more winter for 3 years now. I almost have its replacement finished. Gene

I looked at my old IAC, it didn't seem adjustable, but I didn't force it either.

Watched a few videos on the subject matter tonight. While I understood the function of the IAC, seeing the videos made it even more understandable. Based on what I saw, it seems like the IAC is stuck 'in' or simply not functioning.

The new one is under warranty, so I may just swap it out after checking a few things.

Silly question? Any chance the temp sensor is bad and possibly going open or giving the wrong value to the ECM. Just a thought

That's a good move, my experience with aftermarket sensors or anything electrical is terrible. If the part is NS1 at the dealer, go to Pick and Pull and grab a few.

i have seen temperature sensors act like that when they have a "coating" of sorts on the bulb that sees the coolant.
when shined up to "new" brass, sometimes they come back to life.
would be an easy thing to try.