Howdy,

I have a 2001 5.2l that I had a remanufactured engine put in a couple years ago and have never been able to get running correctly unfortunately. The mechanic that put the engine in for me replaced the IACV because the truck was dying at stop signs when he took it on a test drive. This was because I had a separate issue at the time with the rear axle speed sensor that he did not know about. Once I resolved the speed sensor issue, the truck stopped dying when I pressed in the clutch, but unfortunately still does this pain in the neck start up sequence I'm about to describe.

For the last two years, If I go out and start the truck cold, with out pressing the gas pedal at all, the truck will crank to 400 RPM accompanied by a loud hissing noise out of the IACV port in the the throttle body. After about 30 seconds, the truck will surge and RPMs will land at 400. Over the next 10 to 20 seconds RPMs will slightly increase until the truck surges and then RPMs will fall back to 400. The truck will repeat this a couple more times until RPMs land around 600 and it will sit there and idle fine. To me this looks like the truck is doing a IACV relearn every time I start my truck.

This is where it gets interesting...about 2 months ago I took a TPS and a IACV off of a 3.9l dakota motor I have and installed them on my 5.2l. When I cranked the truck RPMs went immediately to 1200 and held steady for a few minutes. After about 10 or 15 minutes, RPMs finally settled out to around. 600.

After about 2 months of having the truck do the high idle thing on start up, I ordered a new TPS and IACV and put them on the truck yesterday. When I cranked it, it went back to 400 RPM idle and the IACV relearn. I can't figure it out to save my life. I had a new cat and O2 sensors put on the truck about 6 months ago.

One last thing on these IACVS. I have a Launch scan tool. I can tell the truck to idle at 1800 or 2200 RPMs and it will immediately go to that RPM and hold. This is why I can't figure out why it wastes 5 minutes of my life every day doing the relearn on start up...

 

Was the fuel sync set when the motor was installed? Have you checked for vac leaks? I am assuming the throttle body off the old motor was used so was it cleaned? If you haven't used a factory iac it's hit or miss to get one that works correctly.

 

Aftermarket IAC valve as well would be a contributor. I have had zero success with them. Get a genuine mopar unit in there.

 

I called my local dealership last month to buy a factor IACV and they said they discontinued them in 2021. The one I got off Rockauto is either a Delphi or WVE. My fuel sync is showing good (+4 the last time I checked). Throttle body is off my old engine. Never had a problem with any idling issues before engine swap. The reason I had to put a new engine in the truck is the old engine was burning a quart of oil with each tank of gas. I just cant figure out why the truck wants to recalibrate the IACV on each cold start. Here's a different test I did today....


Cold start without touching the gas pedal. Truck started and RPMs immediately dove to 400 with loud hissing coming out of IACV port. This time I right away used my Launch to give the truck the command to go to 1800 RPM. Nothing. It did its first surge and settled back out at 400 RPM. I canceled the first command and gave a new command to 1400 RPM. Nothing again. It surged again and settled back out at 400. I canceled the command and sat there while it did its last two surges and calibrations. RPMs settled out at 600 and it was sitting there idling perfectly like it normally does. I then give it the command to go to 1600 RPM and boom, it goes straight there and holds.

Because it ignored my commands during it's calibration process makes me think it is a computer issue. Why does it think it has to do the IACV relearn on every cold start? If I turn off the truck after it has gone through its recalibration process, and start the truck right back up, it starts and idles perfectly....

 

have you ever reset the PCM, let it re-learn IAC???? Might be worth a shot.

Disconnect the battery, turn on headlights, turn off headlights, reconnect battery. Turn ignition to Run, (not start) count to ten, don't touch anything. THEN start the truck. It should figger out idle fairly quickly.

 

You nailed it. Thanks! I did your procedure and it fired up and went straight to 600 RPM and held steady. It did not do the 4 minute calibration thing. First time in 2 years I got to hear my truck sit there and purr since I put the new engine in.

The only thing I can think is it had some "code" locked in since the engine swap, possibly from my faulty rear axle speed sensor at the time, that kept making it do the self cal thing on start up. Of course over the last 2 years my 6 year old battery couldn't have bitten the dust, which would have led me to the answer. Of course not lol

 

I replaced the battery in my current truck within a couple weeks of purchase, as I thought it was bad, as I had slow crank, 100% of the time. New battery did NOT fix it. So, couple years later, replaced the starter. Imagine my surprise when nothing changed..... Fast forward to just recently, and my battery bit it. Went out to go to work, battery is dead. Hit it with the booster box, drove it to work, when it was time to go home, dead battery.... Hhhhmmmm..... Co worker gave me jump, drove to the battery wholesale place, replaced the battery. Engine cranks right up??? That was interesting. Was my replacement battery from years ago bad when brand new?????

 

Not uncommon for a brand new battery to be dead on arrival. That happened to me with the wife's car recently. The battery had a dead cell. Luckily, I had just bought the battery, so the return/exchange process wasn't too cumbersome and I had the purchase receipt. I always check to obtain the freshest battery on the shelf in the size I need, in addition to popping off the caps and checking the water/electrolyte level. I've seen brand new batteries low on water/electrolyte on more than one occasion.

 

That one was a first for me. And I have bought a LOT of batteries.

 

Unfortunately, quality control is not what it used to be....