High Idle

Having a problem with my 99 5.2 slt durango. Starts up fine but after warming up it idles at 12-1500rpm in drive. I've read a lot of forums posts and they all say IAC valve, which I've changed (twice), TPS, which I've changed (twice). I cleaned the throttle body 6 months ago which seemed to help, or at least make it more intermittent. I could remove it and clean it again but it looks pretty clean to me. Annoying because the high idle burns gas and can be good for the tranny when I'm stopped. I did notice the other day that during the high idle if i barely touch the accelerator the idle would jump up and if I barely tapped it again it will come down a bit. I don't think it's a vacuum problem because it idles fine when I first start it, meaning it idles high and then comes down as engine warms up. It's after I start driving it that the idle in drive goes north of 1000rpm. I could drive this car on level road without ever touching the accelerator but like I said it eats even more gas now and can't be good for tranny. Could the intake manifold sensor play a role in this? Any help would be appreciated.

Well today I started the car and after the cold start high rpm it settled right down to normal after warm up and seemed to act just fine. Driving about 250 miles tomorrow so we'll see how it behaves when I take it out on the highway.

Well it's been all summer and the problem hasn't gone away. Very intermittent. Actually on some days the idle is too low and if I start it up and immediately back out of the garage it stalls. It'll restart but won't hold idle. I have to keep the foot on the gas for about two minutes then it will hold idle. On other days it idles high, at 1500rpm and won't come down. I'm on my second IAC valve. This weekend I took it off and it had some carbon on it so I cleaned it as well as the bore in the throttle body. That worked for one day and then the high idle returned. I'm not sure if it might be another sensor that is doing this but I'm kind of at a loss.

Here it is the new year and I still cant get rid of this stupid high idle. After 3 IACV changes I'm done with that. If I take the throttle body off and clean it along with the IAC it runs fine for a couple of days then right back to high idle in drive. Now I also get a check engine light related to the idle P0505. If I clear it it comes back pretty quickly. Funny thing is when I start the car cold it actually idles low, when it should idle high. After it warms up from driving it idles high in drive 1100 rpms, and when I put it in park it shoots up to 1500. Honestly I can't wait to get rid of this car. It has finally beaten me down.

Have you carefully cleaned the passages in the throttle body for the IAC? I'm not at all familiar with the 1999 Durango, so I may ask some questions that are not applicable, such as have you cleaned the MAF and the Intake Air Temp sensors? Do you have access to a scan tool with a datastream mode to be able to check the engine coolant temperature, intake air temp, air flow, LTFT, etc.?

-Rod

Rod,

I do have a scan tool ODBwiz which is pretty good but when I look at the data I'm not sure if what I'm seeing is nornal or not. I recorded a few minutes of the absolute throttle position. I'll try to post the results here after I graph them. I cleaned all the passages that I saw didn't see any obvious tiny passages that might be clogged. Did not clean the MAP of other sensors. I can start there and see what happens. As usual, thanks for your help and expertise.

Here is the chart of the absolute throttle position. Recorded it while my wife was driving around town. Don't know if it tells anything

So finally gave up trying to solve the high idle and took it into the mechanic thinking it mght be some hidden vacuum leak I can't find. They diagnosed a bad ECM and said cost to replace was 975 plus labor. I said forget it as the car has 215K and is 17 years old. Started looking online and looks like I can get a remanufactured ecm at Carcomputer exchange for 219 plus core charge. Looks too good to be true. Anyone heard of these guys? They state the ECM comes fully preprogrammed to the specific VIN and is basically plug and play. I might just spring for it so I can hold onto the car for 6 more months. In this condition its undriveable.

Got my re manufactured ECM from Carcomputerexchange with updated software and swapped out my old ECM in like 5 minutes (actually instructions say disconnect battery, wait 30 minutes, swap, wait 30 minutes and reconnect battery) and the idle is is gone. Car idles beautifully, actually a tad low but I think after all the fooling I did with the IACV I have to make a adjustment. At any rate I was reading that these ECM's are susceptible to engine bay heat and this car did severely overheat 3 times in the past 2 years so that might explain the ECM getting fried. Cost me 238 vs 1100 at mechanic. And i get a 1 year warranty. Not bad.

Just an update. New reman ECM is working great and car runs like a dream. Perfect idle, no more pinging under acceleration, even with 87 octane. And with justunder 220K on the odometer. This car will run until it rusts our from under me, which unfortunately it is doing at a rapid pace.