have a 2000 Ram 2500 4wd with 81,000 miles on the 5.9 liter. The problem I'm having is any time I cold start or re-start it rough idles to the point of almost stalling then after about 5 minutes of warmup it seems to run fine. took to Dodge dealer & they told me to change plugs , wires, dist. cap and rotor. Did all that and still have problem. Changed TPS, no luck. No fault codes showing up. Any thoughts??? could it be as simple as the O2 sensor or PCV valve? Help!! Thanks for any advice. Rich.

 

if you feather the gas pedal to raise the rpm up to about 1000 does it run better ? if so, replace IAC motor on the back of throttle body.

i doubt that O2 has anything to do with this. i think the pcm starts up the engine in open loop and ignores O2 while it runs on default settings. then after warm up, it goes to closed loop and monitors O2 settings to tune the fuel mix.

vacuum leak maybe? which could be related tp PCV. its only a couple of bucks, so replace it.

 

thanks for the advice. does replacing the IAC motor come from similar experience or are you speculating on a solution? are you saying to replace the PCV 1st before replacing IAC? Thanks again. Rich.

 

LOL, if only you knew!

Doug works for Dodge IAC quality control. He throws out 3 for every 1 he keeps!

What he was saying is the PCV is a super cheap fix if it works. If not, you're only out about 5 bucks, and you can then try the more expensive IAC.

 

Replaced the IAC and the PCV and problem still exists. while it's idling down to almost stall it sounds like its sucking through the air intake big time to maintain idle. After about 5 minutes it just evens out and runs smooth. I don't get it. Still need forum help. thanks. Rich.

 

How many miles on the pre-cat oxygen sensor? If you're anywhere near the 100k mark, swap it out. I've posted the why and how of the end of life failure mode of those critters elsewhere in the forum, if you're curious enough to search. (That's why I always write out "oxygen sensor" -- the forum search won't allow you to search for "O2").

Good luck and happy motoring!

 

Not sure how many miles on the O2 since I;m not the original owner. What about what what dhvaughan was saying about the pcm ignoring the O2 during start up/warmup? Feel like I'm rebuilding my truck $100 at a time and still chasing the prob....

 

I have a 99 with a 5.9L gas, 243km on it doing the exact same thing... rough idle at cold start to the point where you think it should stall, smooths out after about 5 minutes of idling. Same sucking noise too...

I also notice an antifreeze smell after I shut it off, but it's not showing white smoke, and I don't see any leaks. AF level is staying up in the jug, doesn't appear to be any oil in it... weird.

If you figure out what the idle problem is please post it! I'll do the same.

 

try this, its free. (almost)
using rubber plugs, or plugged pieces of vac lines - tag, disconnect, and plug off the 3 or 4 vac lines on the intake manifold, including the big brake booster line. caution - your brakes won't be power assisted! try a cold start and see if it helps. if so, chase the vac leak.

was the little IAC port in the TB clean and not gunked up?

about the O2, its my understanding that the O2 is not monitored during cold start and operation. if so please correct me.

 

Right at/just after cold start the oxygen sensor is ignored, but within a couple of minutes you're going closed loop and it starts getting attention.