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1999 Dakota 5.2L Sport 4x4 Auto 79,210
Miles

Ok guys I've posted in various forums and so far I've had no luck in solving my problem. I hope maybe someone here can help me solve the problem.

When my truck is idling after start up my rpms will drop and the motor will start lopping and you can hear the engine suck air. After a few seconds the rpms will jump back to normal and it idles fine. On the flip side, if I'm driving the truck it'll start misfiring and losses a ton of power. After a few seconds it fixes itself and drives normally. This problem is intermittent and somedays the truck drives great never giving me any problems. Some days it really acts up. After it fixes itself I could drive it as far and as long as I want and it won't do it again until I shut the engine off and restart it. Check Engine Light is not on and has never came on. No codes are showing up on computer. Also, the truck has died before from it dropping rpms although it's not common.

Okay, here is the list of repairs so far:

New Plenum Gaskets Uppers and Lowers and Plate installed
New plugs, wires, distributor cap, and rotor button
New TPS and MAP Sensor (Both Aftermarket)
New Fuel Pump
Checked all lines and hoses. Cleaned and replaced needed ones
Cleaned IAC Valve and Throttle Body
Ran Intake Cleaner through it
Gas treatments
New Air Filter

So far with above repairs the truck still has the problem.

The truck does have an aftermarket exhaust. I bought the truck used and the exhaust was already on it. I was told the exhaust is glass pipes. From what I can tell it has a high flow cat. There is plenty of exhaust flow coming from the tail pipes so I don't think the cat is stopped up.


Yesterday I done more trouble shooting and here is what I found:

When the RPM's drop you can here air being sucked in. I sprayed ether around the intake and sure enough the RPMs surged when I sprayed it around the rear driver side of the intake...

So here's my questions:
is it possible the intake gaskets are blown again?
Could it be a warped or cracked plenum?
Could this be a weak or bad O2 sensor?
Injector problem maybe?

If anyone can shed some light on this problem I would greatly appreciate it.
 

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Let me defer to Niebs and any others who have a clue. Though I consider myself pretty savvy, this is WAY out of my league. I'm only posting to let you know we are reading this stuff, just are quiet because we don't have an answer, or even an opinion!
 

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I second Niebs suggestions. Verify no vacuum leaks from PCV Valve grommet &'hoses, verify booster not leaking (can cause random symptoms exactly as you described).

If however you find it is definitely coming from the intake I would very closely examine it when removed for cracks, straight edge the mating surfaces to verify it's not warped (glass table also works good for this) and inspect the gaskets carefully for indication of sealing issues.
 

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Same problem here, sitting in the dark as to what it may be. Checked all the basics, compression is good, fuel pressure is good, plugs are black which tells me there isn't much of a spark. Brand new coil, battery, dist cap, still nothing. Changed TPS, cleaned up the IAC, checked the MAP, EGR, and CPS, still can't find it. I hear sound of air sucking in when it drops, but as far as I can tell the IAC is functioning and the air is getting sucked in the hole there. I haven't found any leaks on the intake manifold or plenum, which might be something you have, hard to tell. Its at the shop now, I'll let you know what they say and it might be the same problem you are having. Best of luck!
 

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double check teh IAC motor, throttle body can get awful carboned up there, when the IAC is open it will "suck air".... which is normal when it is open. But if it cannot seal due to carbon, there is your roughness..
 
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