98 S1 Disco V8i

When I first got the vehicle I replaced the stepper motor due to a high idle. NO check engine light or fault codes. This is the second replacement stepper motor and the first one only seemed to last about 18 months before the idle started going high again!

Replaced stepper motor, no difference this time to high idle, all holes cleaned etc. stepper motor is seated correctly. No apparent vacuum or air leaks (cruise works ok) but idle still extremely high at 1800 cold, drops to 1000 when warm.

Once in a blue moon the idle does eventually come down to about 850. I am wondering if there could be a stepper motor wiring issue here? All looks good at the stepper motor end but where does the other end connect??? I see it disappearing down by the water temp sensor but can't really feel what is going on after that! Maybe if I can get the cable out I can test for continuity. Arrrggg.

Thanks,
Alan

 

Check all your vacuum lines again. The cruise control has it's own vacuum system and pump and has nothing to do with idle. The fact that the cruise works while rare in a D1 tells you nothing about your problem. Clean all the electrical contacts for the stepper motor and shoot them with dielectric grease to make sure they are making good contact.

 

Thanks, no signs of a vacuum leak and when I unplug the vac from the throttle body there seems to be plenty of suction. Maybe the only way to eliminate this aspect is to replace the hoses completely?

 

Check the hose that is the PCV hose on the right rear.
That hose will rot and the hole most times is on the bottom.

 

Remove your PCV breather hose and pull out the oil separator that is inside the valve cover and clean it with carb cleaner.
Replace the PCV hose, just take that hose to the autoparts store with you and have them cut you a new piece of hose, cut it longer than you need and then trim it once you get home.