My 1997 Discovery XD suddenly can't maintain idle. It was running fine before except got some bad exhaust leaking (exhaust pipe has a hole before muffler and possible bad cat). Then today, the car started but hard to maintain idle. If I kept pumping gas it would still run but rough with less power. At the stop, the idle is low and goes up and down.

Could this be a cat problem? or anything related to it or the O2 sensors?

 

Check the IAC Stepper motor.

 

What is the IAC Stepper motor? Where to locate it? and how to check?

Thanks!

 

located on the Throttle Body Assembly mounted facing toward the radiator. Black round unit held on by 2 small bolts. Has one electrical connector. When the IAC gets dirty it can stick and cause a rough idle or if it dies = stays in one place causing a rough idle. Any check engine light?

 

no check engine lights. my one is a 1997 Discovery 1 Camel Trophy Edition,

 

new IACV from Napa (PART # :CRB 21856). check engine light will not necessarily illuminate.

 

Changed to a new IACV and thoroughly clean the throttle area but it didn't help. The problem stays the same. starts up cold no problem, idles at 750-800 and it drops to below 500 after 10 or 15 minutes ride and then I have to give a bit gas to keep the car running at the stop.

anything else could be contributing to this problem?

 

A bad fuel pump will cause that.

 

maybe a long shot, but check the wiring for the crankshaft position sensor. I'm 4 for 4 on trucks that needed this repaired.

usually doesn't show up until a car wash or heavy rain, but idle goes to crap

 

Just to be clear, is it an XD or camel trophy edition? the camel edition that you could actually buy new at a dealer had a distributor and wasn't sold in North America. There are lots of things that could go wrong with the distributor that can cause idle problems. It would have used a different idle air control than the one listed above so its easy to rule that one out.