My idle issue started about 8 months ago and was hardly noticeable . My truck seemed to miss or idle weird in park for a split second and then go away and it didn't occur all the time. Well it seems to have gotten worse..now its every time I start her up , shell idle up to 800 and slowly come down to her resting point around 625 where she fills like she misses/stumbles and continues till I put her in D..I've tried cleaning tb and resetting pcm and now its doing other things. I took her for a spin after the clean up and she ran like hunting cheetah, alls good right?...as soon as I put her in park the rpms dive to 500 then back to 625 where it feels like she's missing ..I have also changed plugs (oem )sc tuned 91, initial symptoms occurred before the sc was installed, I've also gotten a p0457 twice but chalked that up to gas cap..tightn cap reset and code goes away..thanks in advance, just trying to avoid the whole dealership experience ..

 

Today I got the P0455..evap.leak..hmm..could a bad gas cap cause bad idle..the cap is a key lock, it turns tight but it is a beesh getting the key out..I also think I didn't replace egr gasket when I put a new egr on..cannister..anyone?

 

You dont have a simple small leak you have a large leak. Gas Cap is out.
Lay under your truck, by the gas tank there is a black box with a couple of tubes running out of it check all those tubes for cracks you shouldnt have to look hard like i said you have a large leak, most people have small leaks much harder to find



****
Next time post this in the Tech section and you may get an answer sooner and more people will see it

 

New gas cap and hoses, still messed up. I did the pcm reset and now my truck is downshifting hard at 33 mph..engine light stayed off, but still idles bad in park..looks like its time to go to dealership ..ugh!!"

 

I hope its not anything to expensive, i was hoping since it was a EVAP code it would be a cheap fix. Have you done the simple things like plugs? I know you already cleaned your TB

 

Yeah i stay on top of the things i can do myself. She still does sometimes, my mechanic checked O2's..they were fine. He described it as a slow idle, whatever that means. Who knows, ill get around to the stealer sooner or later

 

I had this problem in my Dakota. Mind you, it was a different engine and I'm no mechanic, but I replaced the Idle speed sensor (what my mechanic called it) and it was good after that.

 

Ive looked into that and was that I would have to replace the throttle body if that was the problem. Thanks for ur input fellas, im just gonna have to live with it for now.