- This topic has 10 replies, 5 voices, and was last updated 10 years, 1 month ago by
.
-
Topic
-
Hey guys. Idle problem on my 99 dodge ram 1500 4×4, 5.2L.
Sorry for the long post.I have been having some intermittent issues of the truck not wanting to idle in the morning. It cranks and fires right up every time, but it seems that the truck doesn’t always want to enter warm up mode where it should be idling high, and slowly dropping rpms as the engine warms up. When this happens I can keep my foot on the gas to keep the rpms high for a few minutes, then let off it, and the engine will drop immediately to a normal rpm range of 600-700. The engine doesn’t like it that low when it is cold, but won’t die either. Once the engine reaches operating temp, everything works fine, drives fine, idles fine.
Now, the issues has gotten worse. Not only will it not idle high on start up, but it actually slowly idles faster as the engine warms up, and won’t go down. So now, at operating temp the truck is running at 1150 to 1200 rpms all the time. It’s almost like the truck has the whole idle process backwards.
I’ve swapped out IAC motors, no change. I’ve pulled TB and cleaned everything, it’s spotless. I have a new battery in the truck, have had the battery, starter and alternator all tested, and they are good.
The coolant temp and air intake sensors all check out fine.
Just because I could, I pulled the TPS when the engine was idling at 1100 rpms at operating temp last night, and the engine bogged down for a bit, but recovered and kept on idling like it was without the tps connected. Not sure if that tells me anything.
I also pulled the connector from the IAC last night while it was running, and there was no change. When I checked the voltage at the IAC connector, I had two powers and two grounds, that were constantly changing polarity, which if I understand correctly is how the PCM keep the IAC from moving the pintle around. That makes me think the PCM had the pintle where it wanted it.
Where should I go from here? What am I missing? Thanks.
-
Replies
-
Check for vacuum leaks with carb spray. no codes or engine light?
http://www.ericthecarguy.com/faq/solving-automotive-idle-problems
Thanks CollegeMan.
Sorry, I forgot to mention that. I did scan, there were no codes, no engine light.I did do a visual inspection for vacuum leaks, but didn’t spray for it.
My hearing may not be the best, but I can’t hear a leak either.
I will try spraying for it tonight and see what I find, and then report back.
For my understanding, I always thought a vacuum leak would make the engine sluggish and run rough, and not what I’m experiencing. Is my understanding wrong on this?
My engine is idling high, but smooth, it doesn’t sound bad.
I agree with Collegeman, a vacuum leak is suspect. I would spray around the intake to see if you notice a change in rpm!
It sounds like you had a dirty or failing IAC. Now that you have replaced it try disconnecting the battery and jump the cables together for 5 minutes. Reconnect the battery and give it a try. The pcm might have to relearn. I think it’s worth a try.
Went searching for a vacuum leak, and didn’t find anything. Tried resetting the PCM for the 4th time, no luck there. So I took it to a mechanic.
Just got a call, and he’s telling me my pcm has an internal short, and I need to replace the computer. I don’t remember the code he gave me, but evidently my scanner wasn’t able to read it, because I checked for codes a few times and came up empty.
He was still looking to find a used unit, was going to call me back with a price.
Any suggestions where to get a computer for cheap? Preferably a fully programmed computer? 15 year old truck…kinda hard to dumb a whole lot of cash into her.
So for the conclusion to this thread…
Picked my truck up from the mechanic Friday night. I made the decision I would try messing with it some more before buying a new computer and installing it.
I went and bought a new IAC…cheapest one I could find was a masterpro from oreilly’s for $27. I wasn’t going to go drop another $100 at the dealership for one like I had just done last year.
I checked continuity from the iac connector to the plug on the computer, and all checked out okay. I pulled the connector from the computer and clean the pcm and connector with some electronic cleaner and compressed air. I also bent down a small tab on the connector to the IAC, just to make sure it was making contact with the iac pins. Stuck the new iac in, and she fired right up.
I’m tempted to go install one of the other two iac valves in to see if the problem comes back, just to see if cleaning the computer and connectors fixed it, or if I had two bad iac’s, but it’s been really cold here, and I’m just happy it’s working again. If I had to guess, I think it probably was yet another bad iac valve.
We’ll see how long this $27 masterpro lasts. If it makes it longer then 18 month’s it will have beaten out the dealership crap from dodge, and at a third of the cost. end rant
- You must be logged in to reply to this topic.