97 disco 4.0 with idle issues

[RonL]

R_Lefebvre,
I have two Discovery, I was swapping parts and see were the problems is. The stepper motor works fine on the other Discovery(1999 Series1), and the 1999's stepper motor does the same high idle on the 1997.

It does stall when I block the intake, no vacuum leak that I can find.

I don't have a problem with resetting the idle, just wanted to know why it would change by it's self.

 

[dallasrover]

Does it have any kind of exhaust leak, that would cause an issue with the O2 sensors? The idle on my 95 D1 was going haywire when I would come to stop. I set the base idle and timing, replaced the gaskets on the exhaust manifolds, and replaced the TPS and it has been fine since.
Has it ever thrown any codes on this? Mine kept throwing #44 for the left bank, then it finally threw # 17 for the TPS after several weeks of messing with it. Mine ran fine at anytime while driving, it would ony happen when I came to stop. Maybe she just has not thrown the code yet?

 

[R_Lefebvre]

I don't have a problem with resetting the idle, just wanted to know why it would change by it's self.

Cosmic rays?

 

[RonL]

dallasrover,
No codes yet, that's what makes this so hard to track down.

 

[justfreeman]

I've actually been running without my iacv plugged in for about a month with the a/c on to keep the idle down. I will be taking my truck to a shop in the next few weeks if all goes well. Please keep us posted if you find out anything else.
ps. I have no codes and no cel either.

 

[dallasrover]

What about the cruise control, is it possible for the vacuum pump to be working incorrectly and be applying some type constant pull on the throttle?

 

[walsnart]

What about the cruise control, is it possible for the vacuum pump to be working incorrectly and be applying some type constant pull on the throttle?

This was the case on mine when had I a similar issue.

 

[R_Lefebvre]

You could try disconnecting both throttle cables from the throttle body?

 

[RonL]

I disconnected the vacuum line from the cruise control and there was no vacuum in the line and the cable was not pulling on the throttle body. So I rule that out.

 

[muskyman]

you are getting unmetered air, most likely from intake manifold gasket.

have you checked all the intake manifold bolts?

I have found a number of trucks with this issue that a number of the manifold bolts are loose.

I have also seen trucks that pass the starter fluid test but yet still are rectified with a new intake/valve valley gasket.

because the design of the intake and gasket there are a number of hidden places they can suck air.

also with lifts with less then perfect driveline angles and MT tires these trucks have a tendency to shake stuff on the engine loose...unexplained high idle...think unmetered air.

 

[R_Lefebvre]

Wouldn't the truck still run when you block the throttle body then?

 

[I Leak Oil]

Wouldn't the truck still run when you block the throttle body then?

If you had a leak that big I doubt it would run at all.

 

[muskyman]

Wouldn't the truck still run when you block the throttle body then?

no not at all, we are talking about small amounts of air to raise the idle.

 

[R_Lefebvre]

I would think any leak big enough to raise the idle that high would have to be pretty big. Doesn't the ECU close off the idle air bypass to try and bring the idle back down, such that it would be fully closed and running purely on the leakage? The systems I've worked on would do that, but they're probably more advanced than a mid-90's Rover system. We're talking about "closed loop idle" where it will adjust the IAB pulse-width to get the idle speed under control.

Is the early Rover stuff just an open-loop idle?