2010 dodge grand caravan 3.8 liter. When in park or at a dead stop in drive or netural idles at 700. When driving foot off the gas idles at 1000 Rpm's and bounces up to 1500 rpms constantly. When braking same thing. Once the rpms hit 1000 it tries to jump up to 1500. I have to really put some force into the brake pedal to get the rmps to drop under 1000. When the rpms drop below 1000 it idles down to 700 and stays there until throttle is pushed above 1000 rpms then it's back to trying to hit 1500 on it's own. I also notice a slight jerk when shifting through the automatic gears. It also hangs on the rpm value when throttle is released. For about 2 seconds. So if I hit the gas and get to 4000 rpms it'll stay at 4000 rpms for 2-3 seconds then drop slowly to 1000 then jump back and forth from 1000 to 1500. No check engine lights at all. Exaust work was done recently I was told when I purchased the van but it seems louder than it should. I cleaned the butterfly on the throttle body while it was in the car. Super dirty. No change

 

Sounds like you have either a vacuum leak which would give you high RPM's. Or the stepper motor or AIS motor is sticking aka Automatic Idle Speed motor. Did you have this problem before the exhaust repair or after. If it was after. I would take the vehicle back and have who ever worked on it and find what happen. Could be something simple.

 

I just bought the van and took it on a test drive didn't notice it then. But the lady I bought it from said she had exaust work done and I saw a receipt that said manifold bolt or something. It's still loud tho. Her son said they took it to a cheap guy and they put glass packs in it. I have glass packs in my ram and it dont sound like that lol. And she was 85. Didn't make sense but I brushed it off anyway. I tried spraying carb cleaner around the vacuum lines and throttle body and where the the lifter cover meets the block all around really and no extra rev sounds. ...... cleaned the throttle body while it was still in the van. It was super dirty. There is a little white smoke when u start It up out of the end of the exaust pipe. Oil was really low to when I checked it after driving it a lot after a 4-5 days. Dont see any drips tho. And she had an oil change right before I bought it. Within 100 miles of me buying it. I crawled under it and the front middle suspension is covered in something. It was mainly black but it's been raining aloft and the top layer of of grime I saw some red in it. So I thought maybe tranny fluid. So I did the dip stick trick and measured it cold and seemed to be good. That's about all I know between the first post and this one

 

Check the hose going to the brake booster too. Make sure there is no leaks.