My 97 disco idles really high when i first start it up (2500) but by the time i get to work (30 min 26miles) the idle is where it should be when i put it in park. Im just wondering what this could be since the reading ive been doing describes a problem where the idle never comes down, where as my situation is the idle comes down after i drive it. Any help would be appreciated.

 

Two things have a lot to do with idle. The Idle Air Control Valve (IACV) is a 200 position stepper motor that computer controls a vacuum leak and rules the idle. It can be easily cleaned by removing from the throttle body, spray very well with carb cleaner, do not adjust the tip, and also clean out the bore it its in. While you have the carb cleaner take apart the air hose and clean the throttle body butterfly valve with same stuff. NOTE: Do not clean the MAF sensor with carb cleaner. If doing that job, use a spray made for MAFs and only do when truck is stone cold and you have not switched on ignition - which powers up the sensor to 350F at one spot inside, and will not like cold spray. A new MAF sensor is $1400+....

Any vac leak can impact idle, and these can change with engine warming. Look over all vac lines and the rubber hose from MAF sensor to throttle body for cracks.

A second thing that can be involved is the engine coolant sensor, if it was "bad" it may be showing the computer a low temperature, the computer asumes you have driven to Alberta and need more fuel to warm up the truck. A code scanner attached to the OBDII diagnostic port (like at a parts store) can show you what coolant temp is. Should be ambient or logical. My ECT reads -40F when unplugged.