On Friday I took the battery & battery tray out of my '97 5.9L to fix a vacuum leak at the cruise control unit, under the battery tray. 1 hour later I put the battery back in and fired it up. It started a little rough, but idled fine. It ran fine, ran some errands, all good. Saturday morning it wouldn't start unless I held my foot on the gas pedal lightly, and when it started I had to keep my foot on the gas for 5 minutes, until it "learned" how to idle again. Drove the truck for about 30 minutes and it ran great. 4 hours later, again it wouldn't start without a foot on the gas. 30 seconds later, it ran fine again. Is it the IAC motor, just below the air filter, or how else can I get it to idle cold again? Can that little motor be tested or something? Or the butterfly in the intake need cleaning? I'm sure it's related to having the battery out for an hour.

 

Clean the throttle body. Pull it off, remove the IAC motor, and clean everything up really well. (just wipe the pintle on the IAC off, it's rather delicate, and you don't wanna turn it.) Leave the battery disconnected while you play. Put it all back together, hook the battery back up, turn the key to "on" (not start, and don't touch ANYTHING) count to ten. Start the motor. Let the PCM figure out how to idle the engine again. Should take care of it.

 

Update: Problem fixed itself. Guess the truck re-learned the cold idle on its own, as it has done in the past. Running like brand new again. 408,000km and almost all original truck. No major repairs. Original owner!

 

This happens to me from time to time if I unplug the battery for a while, or if the battery dies form sitting. I end up driving it around for a few miles till the computer relearns the idle speed. It's a bit annoying when coming up to a stop sign or having to slow down. But it learns the idle speed fairly quickly after driving it some.