97 disco 4.0 with idle issues

[RonL]

Problem - idle in P or N is 1750 to 2250 RPM.
idle in R or D is 1000 to 1250 RPM.

No CEL

97 Disco 4.0 with 142,000 miles, just got back from a 2,000 mile trip where everything worked great. Now I am home and the idle is acting funny.

What I have replaced....
TPS, no change
MAF, no change
Stepper motor, no change
Plugs and wires replaced before the trip.

Any thoughts were to look next?

 

[R_Lefebvre]

Vacuum leak somewhere?

 

[justfreeman]

I have been trying to figure the same thing problem out for a while. Mine has been doing the same thing since I cleaned the throttle body. What most ppl have suggested was to have the ecu reset to clear the adaptive values, that apparently don't always reset themselves, with testbook or its equivalent. But as someone else mentioned, eliminate the vaccuum leak possibility first, and please let us know what you find.

 

[One4adventure]

I assume you have checked the throttle cable is slack at the intake?
It should have a little bit of free play.
If its tight it can indicate the gas peddle mechanism is not returning fully, it happened to my 97 and a liberal dose of WD40 got it moving again.

Good luck,
Chris

 

[RonL]

Yes, the cable is a little loose, the butterfly seems to be shut fully.

 

[timmy!!!!!!!]

Good luck. I have been trying to figure the problem ot on both of my discos.

 

[jrose609]

Tim

Check PM's

Jason

 

[RonL]

Update...
Replaced all vacuum lines. no change in RPM.
Sprayed the engine while running with Carb cleaner. no change in RPM
Sprayed the engine while running with starter fluid cleaner. no change in RPM
Unhooked the MAF while running, RPM dropped to 650-700 and it run okay. Hooked MAF back-up, RPM were 650-700 for a minute then returned to the 1000-1250 range.

It looks like there is no vacuum leak, but that is all I know...

 

[I Leak Oil]

Have you had anyone scan it for any codes? Maybe a temp sensor?

 

[RonL]

I have a $100 code reader, that will reset CEL. The CEL is not on, and I have no codes.

 

[RonL]

update...

TPS is causing the high idle, but it not that simple. It acts like I need to re-zero the singal to the computer.

Here is what I have found, when I swap TPS between my two Disco, the 97 always runs a high idle(1750 to 2000) and the 1999 Series 1 idle okay, no matter which TPS it has. This tells me the TPS is okay. Voltage at the wiring harness is the same in both Disco, so the ECU computer must be okay.

If I un-bolt the TPS and leave it plugged in, it idles fine, when I hold it in place and line-up the bolts, it idles at 1750-2000 again.

What would cause the computer and TPS to need to be re-zeroed?

 

[R_Lefebvre]

I'm not sure why the TPS would affect the idle speed in any case. Sounds like a weird system. <shudder>

Just going on a "fishing trip" here, but I'm curious what happens if you leave the TPS plugged in, but disconnect the O2's. Or, try TPS connected, but disconnect the idle air bypass.

 

[RonL]

Justfreeman,
To test what I have found, unbolt your TPS on your Discovery and hold it in place, then rotate it both directions and see what that does for you idle?

It is easy to remove, two trox #20 screw tips and a small ratchet.

R_Lefebvre,
unhooking the Idle air does not change the idle.

 

[R_Lefebvre]

And, you've already replaced the idle air bypass solenoid? (Stepper?)

How about... remove the air intake tube from the throttle body, and block the intake with something. Whatever it is must be solid, and capable of sealing decently. Preferrable a piece of flat metal. Whatever it is, can't get sucked in.

If it keeps running with the intake blocked off, you *have* to have a vacuum leak somewhere. If it stalls, there's either something wrong with the IAB system, or your computer is doing something odd.

 

[sven]

Have someone with a testbook reset your idle. Unfortunetely there is no other way around this.