Well my disco has not been driven in a few days, I go to start it and it goes up to 1800 rpm. it slowly starts to drop over a minute then at 1200 rpm it drops to normal idle. This has a brand new stepper motor and new ecu. I had this issue before but it stayed at 2000 rpm and ran like crap. So does this happen to anyone else? The throttle body is clean and so is the stepper motor and the hole.

Once at a normal idle it stays that way. I have noticed over the past couple of weeks that when you sometimes start it it will go high but immediately drop down (when cold). Seems that it is getting worse slowly.

 

When I first start mine it shoots up to 1200-1500, then drops back down immanently.
It has always done this.

 

This went to 1800-1900 rpms for 1 minute. This is not how it normally acts. Any ideas what to look for?

 

Other than vacuum leaks...no, not off the top of my head.
Did you have the new stepper motor and ECU synced?
Sometimes, not always, but sometimes the new stepper motor needs to be "programmed" to the truck.

 

oh yeah, land rover did it, the gems system had to be programmed for the vehicle. they set the base idle and installed a land rover stepper motor. spike, i dont know if you remember, i tried the jeep 4.0 stepper motor, then bough a third party one for it. it still idled high and then i took it to rover with a new(used) ecu. they reprogrammed it, installed a land rover stepper motor and programmed that, and i was good to go after $600. the issues i had the first time were way worse than this, the high idle this time just has me worried that I am going to have a repeat performance.

 

Yeah I remember now.
Sounds like a vacuum leak then.
Back of the engine, intake plenum and valley pan gasket are common hard to find vacuum leak points.

 

if its dropping down in stages like that, im thinking your iacv is being commanded to open... check the connection to your engine temp sensor and the fuel temp sensor

 

If Rover set it up and supplied the parts, you have a 1 year warranty and should go back to them for another try at getting it set right.

 

they supplied the stepper motor, but not the ecu. I know they said they would not warranty the ecu. Hopefully they will still honor the stepper motor.

where is fuel temp sensor located?

 

its the sensor that has wires goin to it on the fuel rail thats not an injector... drivers side front of the rail i believe, but im tired right now, so who knows... i agree with mike though, did they say it needed the iacv? and why did you replace the ecu?