I have a 99 with 5.9. About 4 months ago, I went away for a while. When I got back my truck started, stalled and then w/n start unless the gas pedal was mashed to the floor. I threw a new idle air control motor in and all seemed fine. I didn't have to do a relearn for the new sensor or anything...it just worked like it did before.

About 1 week ago, I got a MIL of PO505, so I figured the IAC I put in was junk and had a short life. The engine was running fine...just the light. I figured I would do a warranty swap before it got worse and wouldn't start again.

I changed it yesterday and this time when I changed it, I had a bit more time so I cleaned out the carbon from the port with intake cleaner and shop air...it was pretty dirty. I reset the light and it stays out. When I started it up, I had an initial rough idle (I think due to residual carbon and cleaner as I also sprayed the TB a bit), then the RPM's started a steady rise up to about 1500. I read then is a learn procedure of running the truck at 40 MPH while at operating temp. That was no help. I tried all kinds of speeds for about an hour; all the while the idle is so high that I have to fight it at a stop. In gear the idle is about 1k, out of gear it’s between 1.5-2k.

Now I am wondering if my initial problem was just carbon build up (that I didn’t clean at first) and if the high RPM’s are due to a possible vacuum leak or other malfunction. I’m not sure there is a “learn procedure” as I can’t find one anywhere in the shop manual. I was thinking of pulling the TB and giving it a proper cleaning....or maybe a seafoam bath (is this a good enough cleaning?). I don’t want to waste time chasing my tail if the real problem lies elsewhere. Any thoughts or input would be greatly appreciated :-)

 

A bit of an update... When I started the engine today, the engine ra a bit rough (like when I started it yesterday) and the RPM's were about 900...not too bad. They seem to jump around a bit up to 11 then 12 then down to about 8 and it started to sputter. it seemed to start creeping up after that. Could it be a bad MAP sensor (or dirty/sticking)? I checked a few vacuum lines with my hand tester and all seemed ok. I am just got a spray bottle of water to see if I can find any leaks. If not, I will either sea foam or pull the TB.

 

Did you remove the negative battery cable when you cleaned/replaced the IAC ?

 

No, I only reset the MIL with a scan tool.

 

Anytime you are working with the sensors or anything electrical for that matter, you should remove it. What brand IAC did you install ?

 

Duralast from Autozone. I tried to disconnect the neg and wait a while to see if it would reset. I cut some tree limbs for the past hour and then reconnected it. Same problem. I did find however that when it first starts, the engine reves up to about 1K, then if you give it gas, the RPM's w/n go below 2K. If you turn it off and restart, the RPM's reset to about 1K, untill you give it gas again. After reading in the 3rd gen manual (the second gen manual had no detail of operation), this makes sense. According to the 3rd gen manual, the IAC zeros out every time you start the engine.

That being said, either someother sensor or malfunction is preventing the ECM to drop the idle, or it may just be as simple as another bad IAC!

Any ideas?

Thanks

 

DuraCrap, Get your money back and get one from the dealer or at the least a Standard Motor Products brand. And this time disconnect the Neg battery cable first.

 

New update:

I took the old mopar one and manually positioned the piston all the way out. It’s hard to move but it can be done, not the duralast though, they won’t budge. With it fully extended (about .75 inches), I was back to where I was a few months ago…only runs with foot on gas. I measured the position of the “high idle” one to be .25 inches to the base of the piston and the one that ran good but caused a light to be .5 inches. I manually set the old mopar one to .5 and now the idle is ok. Out of gear it’s just at 1K and in gear 800-900. Tried the road trip idea again to see if it would “fine tune”, but nothing changed.

I did also try to see if they moved on key position and none of them did. I didn’t do it while in the crank position though. Does anyone know anything about the circuit or any specs for this motor? The book only shows the 4 wires going to the PCM but no voltages or grounds. According to what I’ve found, the PCM pre-positions the idle air control (IAC) during ignition (key on) mode. The IAC is a stepper motor. The IAC is called a stepper motor because it is moved (rotated) in steps, or increments. It has 4 wires with 4 circuits. Two of the wires are for 12 volts and ground to supply electrical current to the motor windings to operate the stepper motor in one direction. The other 2 wires are also for 12 volts and ground to supply electrical current to operate the stepper motor in the opposite direction. It is sued during braking calculations, idle (of course), acceleration and load factoring etc.

It all makes sense and seems logical, but mine doesn’t move and the truck runs fine (with no MIL light)! What gives? Does anyone know which wires do what? Any test procedures etc?

 

Replace it with a new one. You just ruined it/them by moving the pintle.

 

... ok, but I only moved (or in the case of the new one that didn't move) after it was malfunctioning already so I don't think I ruined it... it came pre-ruined ;-) The one I moved was just a temp fix so I can drive! I only posted the distance info fyi.