I'm having a problem with the idle remaining high, 2,000 rpm and sometimes higher, between shifts. The idle will remain high until I stop and the PCM tells the idle air control valve to go to base idle, which is running about 800 - 850 rpm when hot. Unplugging the IAC valve results in a drop of around 100 rpm. The problem is worse when the air conditioner is on in that the idle will sometimes remain high for about 10 seconds after I stop then immediately drop to 500 rpm and bounce back to 850 rpm. It has stalled a few times. Several times I've had an issue with loss of power under load. No codes have been set. long term fuel trims indicate 15-17% and drop when opening the throttle. It's behaving as if there is a vacuum leak. I had a minor vacuum leak around the intake manifold gaskets and I have replaced the intake gaskets along with the leaky valve cover gaskets, and while I had things apart I replaced the injectors along with new seals. The PCV valve has also been replaced along with vacuum tubing. While troubleshooting I've smoked tested and plugged off all ports to see if I could find a leak the smoke test didn't reveal. The only thing I haven't been able to test is the EGR valve because it's inaccessible without a lot of work. The only thing I found was a very small leak from the intake manifold gaskets. Replacing them didn't resolve the problem. Sensor data appears to be where it should be and I'm here seeing if anyone has any ideas before I start firing the parts canon at it.

Also, it's a manual. If I leave it in gear this issue will problem the truck at 20 mph without touching the gas pedal. I did check the throttle for binding. No binding. IAC was also cleaned with no change.

 

The idle up between shifts/coasting in neutral is to keep the catalyst warm to increase the effectiveness of the catalytic converter, if I recall.

This idle-up is also partially commanded by vehicle speed. If it happens constantly, and erratically, your speed sensor might not be working as well as it should.

 

Yes, I understand the purpose of a higher idle between shifts. Its to reduce NOx emissions. The specifications for the idle speed between shifting is 1300 rpm at 30 mph to 1750 rpm at 55 mph, . It shouldn't hang at 2000 rpm when coasting to a stop, which is what it is doing. I can also duplicate the problem in the driveway, so it isn't a speed sensor issue.

 

I’m having the same issue on my 07 manual 2.3