Hey all,

Looked around at different Dakota Forums , so I figured I'd throw it out here.

It's my boys truck, 252k miles on it. only worth about 500 bucks. He went and got gas at lunch, then about an hour later tried to start it, the truck would barely idle. sounded like a jet engine sucking air at the same time. When you step on the go peddle it got worse, when you let it off, it stumbled, then raced, then back to rough idle.

Told him he may have bad fuel so he put in fuel conditioner and let it set over night. the next day we towed it to my diesel mechanic to get codes. There is a bracket for an ODBII plug, but no plug in. there is a factory wired ODBI plug in the engine compartment, but you can't get codes from it as the VIN indicates it is supposed to be ODBII. the good news was it was idling fine when we towed it, but it would still stumble when you pressed the go peddle. If you pressed very slowly, you could get RPM's up to about 1500, after that it would stumble and go to a rough idle for a bit.

Put seafoam green in, let it set over night, and ran the rest of the gas out. Put fresh gas in today. Idle is better, but still stumbles when you try to give it gas. It will hold 1500 if you raise it up slow, but if you do it fast, or try to go above that it stumbles back down to a rough idle, then smooths out again. It can be driven, very carefully, but only in first gear and with little if any gas peddle pressure. If you try to rev it, it just stumbles, tries to die and then eventually sill return to smooth idle.

Besides, the over the cliff version of fixing the problem, any ideas where to start without throwing parts?

thanks in advance...

 

I'm no expert by any stretch of the imagination, but my little man-van did the same thing last winter. Turned out to be a vacuum line that had rotted. My problem didn't come on all of a sudden tho. It was gradual over a period of a couple of weeks until it got to the point you're at now. It's starting to do it again very slightly now, so I'm thinking I have another vacuum line starting to head south.

 

Sounds like a vacuum leak or TPS going out. There is something about those V8's and the sound you are hearing. (Sucking air like a jet engine) My 98 gasser 360 V8 would sound the same but not all the time and there was nothing wrong. That is just how it would sound.
Spray carb cleaner to find any vacuum leaks. I bet that is the problem.

 

I am no master mechanic but it sounds like a vacuum leak to me. Other than the carb cleaner, another way to test for a vacuum leak is to use propane, in ventilated conditions. Do whatever it takes to make engine run rough. Then use an unlit propane torch. Spray the propane stream over vacuum lines and fittings. If you get to a leak, the leak wull suck in the propane. Propane is combustible, will get sucked into the vacuum system and will burn and smooth out rough condition. Bob's your uncle - you know where your leak is.

 

Sweet... Propane, fire, combustion, my favorites!!!

 

In the V-8 there is an idle servo that controls idle air when the throttle is closed. It has a tendency to hang up and cause idle issues. Idle Air control (IAC) Motor is mounted in the throttle body. Good de-carbon cleaner would be of benefit to clean out those ports as well as the MAP sensor for connection and clean. AFter that is done, i would suspect plugs. Bad plugs don't like idle.

 

Ok the IAC. Is it on the back ( firewall) side of the butterflies? There is a hole there where air is being sucked In causing the 'jet' engine sound I referenced in the op. I disconnected the electronic controler connected there (out side of the housing) and it made no difference.

 

That servo controls idle air for idle speed. If it made no difference, I would suspect its plugged or seized up.

 

I removed and cleaned up the IAC and reinstalled. I can see it operating with throttle movement. It idles fine, very constant right at about 600 to 700 and very smooth now. If I slowly increase throttle it does ok until about 1800-2000 RPM then it dumps and shudders. If you hold the throttle position where it dumps it shudders then races then shudders, with an occasional backfire through the throttle body, which scared the heck out of me so I let go of the throttle linkage. If you increase throttle rapidly it dumps and shudders as well. I am thinking MAF or TPS at this point.

What do you guys think?

I wish there was a way to pull codes, like the key trick with our trucks.

 

Is there a tach in the truck? Just wondering if when it starts to sputter if the tach goes nuts.

 

Yes there is. I would have to say it represents what the engine is doing pretty accurately.

 

With the IAC motor in place there should be no air leak. What are you saying?

If it is leaking the MAP is not going to give a correct reading.

 

Umm

4BT swap?


I concur with the vacuum leak theory. PIA to hunt down sometimes.

 

make sure that any of the EGR connections are not leaking as well. had my mazda do a similar thing when we did headgaskets on it last year, found the air leak and it smoothed right out.

break out the propane or carb cleaner and start lookin for leaks like said above.

if it is idling good but then starts to buck and fart at half throttle, maybe just maybe the 2ndary windings on the coil are fried. seen that too

 

I replaced the IACV on my 87 Chevy 305 V8 a few years back. I seem to remember it was an inexpensive part and took about 10 mins to R & R. Throwing parts at a prob isn't always the best way to go but in this case it is a cheap and easy option.