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1998 Ram 1500 5.9 Idle Problem

5K views 6 replies 2 participants last post by  key99 
#1 ·
Alright, I have been searching high and low for an answer to my truck's idle problem, and every single time I find a thread relating to a rough idle, their problems go farther than mine. As the title says, I have a 5.9 Magnum with only 85,000 miles, the truck has lots of power, sounds great, no engine codes to be seen, and doesn't use up oil (I am also using Mobil 1 Full Synthetic). Now to my dilemma, every time my engine gets cold, and by cold I mean when I let it sit there without running for a few hours, I start it up and runs fine for about 2-3 minutes. Suddenly, it goes into a rough idle, as if it has a lopey cam, and gets way below the standard idle RPM (I also can't tell the EXACT RPM because I have the Instrument Cluster without the Tachometer). Here comes the difference between my problem and everyone else's, when I start to drive away, it returns back to normal. It doesn't die or go back to a rough idle when I stop, I sat at Taco Bell in park for a good 45 minutes with no problems. But when it sits for 2 hours, and start it back up it does the rough idle.

I already cleaned the Throttle Body and got a brand new Idle Air Control Valve, any advice on what I should do next?

And it does have a hissing noise from the engine when it does the rough idle, and that's the only time it hisses or acts weird. I didn't check to see if I had a Plenum leak, but it doesn't use oil so I don't think that's an issue?


Any help is greatly appreciated :D
 
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#3 ·
#4 ·
EVAP issues wouldn't trigger a check engine light?

I also forgot to mention this: When I bought the truck a month ago, it started up fine, no issues at all. I drove it all the way home from Albuquerque to Carlsbad (about a 4 hour drive), no issues whatsoever. My dumba** wanted to have the engine cleaned, so I asked my dad what would be the best way to do this. He told me clean it with the engine on, so if I'm spraying something that doesn't want to be sprayed, it'll tell me. I know not to spray directly at certain things, and to spray far away if I do. When I went to spray the engine, I didn't hear anything wrong or it bog down. When I was finished, I got in the vehicle and it came up with a Check Engine Light Flashing as soon as I started driving, I was misfiring on 4+ cylinders. I pulled over, turned it off and turned it back on, the engine light went away and everything was fine.

But now I have that idle problem.
 
#5 ·
Again, "guessing", just a possible check/search direction (bump seemed desperate).
... FAIK, no 1500 had a leak detection pump for EVAP; some bigger rams (HD??) had them.
... IIRC 98 still has EGR valve; again just a "guess", costs nothing to check.
 
#7 ·
Ya, replies kinda thin, likely due to thanksgiving holiday(and might be the only chance some fellas get to fix the ram); the haven't a clue/guess is kinda a search direction, better than nothing, costs nothing. Thanks for keeping everyone posted about outcomes.
 
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