So I've been having this issue for a while and recently have started to investigate it. For some reason my idle holds at 1500rpm until I come to a dead stop. I did some research and found out that some cars came with deceleration valves that would purposely do this to prevent a rich condition which could foul catalytic converters. I talked with EuroCharged and Jerry is unaware how to bypass this feature in our cars since we have electronic throttles. I've checked every vacuum line and every connection is held down with ring clamps and still not resolved.

This only happens when the car is warmed up, I also have cat codes P0422 and P0432 so it could be possible that the idle is holding because it's trying to get the cats up to temp.

If the cat codes are possibly the cause for this then I'll probably have to get those replaced even though I don't have emissions testing here.

 

Solution Found:

Turns out the problem with the idle had to do with my cats being clogged and possibly creating too much back pressure. Since I have fixed the cats my mileage has gone up which is pretty awesome.

 

Thank for the update. Did you "fix" it by deleting just the rear cats? Fronts were o.k.?

 

No my cats are still attached I just unclogged the front ones and the problem has gone away.

 

Hi folks, new here and having exactly same high idle situation except no codes at all. No performance loss. Rpm just hangs there until I come to a stop.
what would be your advice, what should I do first?
Regarding catalytic converters, how do I declog those and do I even touch them?
Appreciate any input.

 

I'm having the same issue for about 3 weeks now. My car is a manual and whenever I put it in neutral, it hangs at 1,500 rpm for about 5 seconds and then drops off. Last week, the car would not start (tried 4 times - cranked perfectly, but no start). I let it sit for 15 minutes and it started but the check engine light was lit up. I removed the engine cover and reinstalled and the problem went away for about 5 days and is now back.

How does one "clean the cats"? Thanks for this post Selbyl

 

If you think it is cats, there is cataclean you can get at most autoparts stores.

on my 6 speed it has done that for along time.
when slowing down I just slide out of gear at around 1,000 rpm (no clutch) and rpm stays down, but if I shift out of gear at even 1,500 rpm then the rpm will hang up there.
I do not have rear cats and dual exhaust.

 

Thanks for the tip!

 

I actually fixed the high idle issue last night.
When I acquired my Crossfire it had an aftermarket straight through muffler which was very loud for me (lots of drone). I replaced the muffler with a chambered one and now exhaust tone is much better and the drone is gone, so is the high idle! It idles normal now.

 

A 4' piece of 3/4" black iron pipe cleans the cats with the benefit of lower restriction overall. Woody