Help Solving High Idle Issue

[Bitar100]

I have a manual 2003, 4.0 and the engine is having issues with idling correctly. The rpms rise when I am putting it in neutral , when im pressing the clutch or when im braking and coming to a stop. Also my rpms are taking longer to rev down it’s very noticeable. It basically stay at certain rpm range and doesn't go down when its suppose to drop right when u put it in to netural but I have to rev the gas pedal a couple times for it to go down or sometimes I have to open the hood and press the throttle flange closed.


I know the majority of issues with high idling are caused by either a vacuum leak or a clogged IAC or dirty throttle body. I inspected around for vacuum leaks and found two wearing items . I replaced the elbow rubber going to the first port of the intake manifold and put 2 clamps down on each side. I found a broken AC vacuum line so I replaced the entire line for that. After replacing those two suspects, I performed a vacuum leak test with air pump and cigar... pumped out the entire cigar in there nothing was coming out of anywhere . I checked everywhere underneath the manifold side around no smoke was coming out anywhere.

If there is no vacuum leak, is the best option to resolve this issue is to replace the TPS and IAC with new mopar ones because they've never been replaced....... (and worst case scenario if that doesn't resolve it what would you guys do next?)

 

[hosejockey61]

Did you try cleaning the idle air controller? There are write ups in the how to section here in the forum...

 

[Bitar100]

Did you try cleaning the idle air controller? There are write ups in the how to section here in the forum...

Yea I did I followed everything in the forums. cleaned it the first time with spraying tb cleaner in the inlet with holding the rpms and then I took out the iac after and cleaned it too it wasn't dirty or gunky as I have cleaned it before not to long ago

 

[HornedToad]

I had a very similar high idle problem. I addressed all the vacuum fittings the best I could, then did a smoke test with a homemade smoke machine. I didn't see any smoke coming out. Then I changed my IAC and TPS--still idled high. Then I looked more carefully for vacuum leaks and found the big culprit to be the rubber hose connecting the crankcase ventilation tube to the intake manifold. It was making a very faint hissing sound and if I wiggled it the hissing changed. Just for kicks I hooked up my smoke machine and pumped more smoke in and none came out there (now I know the smoke test isn't as reliable as I thought). I replaced that rubber section of hose and my high idle problems went away. Yours may or may not have a similar leak but I would take another hard look at vacuum leaks before you start buying new sensors and stuff..

 

[Bitar100]

View attachment 207421
I had a very similar high idle problem. I addressed all the vacuum fittings the best I could, then did a smoke test with a homemade smoke machine. I didn't see any smoke coming out. Then I changed my IAC and TPS--still idled high. Then I looked more carefully for vacuum leaks and found the big culprit to be the rubber hose connecting the crankcase ventilation tube to the intake manifold. It was making a very faint hissing sound and if I wiggled it the hissing changed. Just for kicks I hooked up my smoke machine and pumped more smoke in and none came out there (now I know the smoke test isn't as reliable as I thought). I replaced that rubber section of hose and my high idle problems went away. Yours may or may not have a similar leak but I would take another hard look at vacuum leaks before you start buying new sensors and stuff..

I also replaced that rubber/plastic hose not to long ago and I made sure to remove all the rubber fittings and looked for cracking I did that one you mentioned too I took it off no signs of cracking . Not sure now if that smoke test was any good

 

[Bitar100]

Update:
I was planning to replace the TPS and IAC with mopar brand new ones but I went to autozone before hand to test their products (I know its a big No No for sensors from autozone but I was just testing them). I purchased TPS replaced it and got no good news it was still high idling like it was doing no change. Returned the TPS to autozone and got a IAC from them to test it out ... they sold me one that was much shorter and different then the oem but it said it would fit in their system. I tried to just see what would happen if I install it.... it didn't fit fully and ended up giving me a P0505 code for IAC. I returned the IAC and put back the OEM one.

I reset the codes unplugged the IAC connection and the code reset so im guessing that means from what I have done my TPS and IAC are functioning and are working? Or just the TPS?

 

[Bitar100]

Anyone have any advice on what I should do next to try fix this?

 

[Goatman]

Had similar issue on an old (52) Dodge truck. Seems like every half century the carb return spring needs to be upgraded to a slightly stiffer one. Also be sure all the linkage is well lubed and working smoothly. You could even add another (light) spring or even a decent rubber band held on with paper clips () but the band will get hard from the heat and need replacement every few months. But is a cheap and easy way to see if it will work for you.
Still be certain to have all vacuum leaks are dealt with, tho.