Hello All,

I recently bought a 1998 Dodge Ram 1500 Laramie, 4x4, with the 5.9L gas engine. It only has 98,000 miles. I lived a bit aways from the seller so we agreed to meet half way. Long story short, met the seller, truck ran and drove great(truck was warm from him driving it to the meeting location). Bought it and came home. A few days later, went to go and start the truck and it has a really erratic idle when it first started. Sounds like it has a really loppy cam in it. Anyway, it will clear itself out after about 30 seconds and idles great afterward(600/700 RPM)or once the truck is warm. It then idles fine the rest of the day too. It only does this on cold starts. Some times it bad enough it will kill itself out and you'll have to hold on the gas for a few seconds to keep it running.

I took the throttle body apart and gave it a really good cleaning. It was super dirty and gummed up. I believe the port to the IAC was almost clogged. I got the throttle body pretty much spotless, all ports cleaned and cleared, and cleaned the IAC. Start the truck up and immediately the trucks idles great on cold starts, no erratic idle, but I noticed its now idling at around 1,100 RPMs. I unhooked my battery and left the light switch on overnight to try and drain and reset the PCM. Put the neg cable back on the next morning and again, truck starts great and idles great but still idles at 1,100 RPM. Sounds like the PCM reset didn't effect anything.

Could I have damaged or changed the adjustment on the IAC when i was cleaning it? Also, the previous owner replaced the cat and both O2 sensors before I bought it. I also checked for vacuum leaks with starting fluid but did not find any.

Any ideas?

Thanks!

 

Reset the PCM again. All ya gotta do is disconnect the negative battery cable, turn on the headlights, turn off the headlights..... Hook the battery back up, turn the key to Run, (not start) count to 10. DON'T TOUCH ANYTHING while you count. Start the truck. Should figure out idle right quick.

What this does is it forces the PCM to 're-zero' all its sensors. Including the IAC. Give it a shot, see what happens. If it still idles really high, look for vacuum leaks.

 

Did the PCM reset again per your instruction. No change in idle. I checked for vacuum leaks with propane and starting fluid but did not find any. I went ahead and punched out the cap on the idle set screw and tried to adjust it there but no change in idle. I backed the screw out far enough there was a gap between the end of the screw and throttle plate but that did not change the idle any. Still sits at about 1,100/1,150. Yes, I did precisely count my turns on the idle set screw and did put it back to where it was.

I hate to just throw parts at it but a new IAC is only $30 at the parts store. Might just try that???

 

id try putting hand over the opening on top of throttle body for iac.. if it idles down then it would mean vacum leak if stalls than iac or atleast i think..i have also had a vac leak on my 99 that was around studs that mount brake master cylinder to booster .(took me a month to find that one)

 

Go with a mopar IAC, I had serious issues with the aftermarket one I bought. Stalling was only the beginning.... Swapped in a USED Mopar IAC I had layin' about, problems went away.

Need to see what PCM thinks idle is, and what it thinks target idle should be.....