V8 idle speed

The idle speed on my Discovery is very eratic, almost feels like it going to stall sometimes. I have taken out the idle stepper motor and cleaned it but its still the same. I did read somewhere that if I disconnect the plug with the engine at idle the speed should increase to approx 2000rpm. Can anyone confirm if this is correct? How can I test it? If I need a new one, how much is it likely to be? When switched to lpg its lovely and smooth. Thanks Richard

Reply to
Richard
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You think you have problems, the idle speed for me depends upon my ability to keep my heel on the brake and my toe on the accelerator

Reply to
Larry

Aah, that'll be the laws of Bistromathics, then? All to dow ith waiters, their movements and scribblings, apparently. (Ask Slartibartfast if you're unsure!) Badger.

Reply to
Badger

On or around Thu, 26 Jan 2006 21:20:08 GMT, "Richard" enlightened us thusly:

which model engine/vehicle?

Reply to
Austin Shackles

"In Relativity, Matter tells Space how to curve, and Space tells Matter how to move. The Heart of Gold told space to get knotted, and parked itself neatly within the inner steel perimeter of the Argabuthon Chamber of Law."

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Reply to
Natalie Drest

oops, should have said....its a 1995 Discovery 3.9.

Richard

Reply to
Richard

When was the last time you cleaned out the plenum chamber and the idle bypass ports?

Disconnecting the plug from the stepper motor will just stop the stepper from operating therefore no idle compensation will be made.

First trick. clamp the hose from the stepper motor connection to the port just next to the throttle body ( hose is about the size of your thumb) with the engine already running, Idle should reduce to what is called 'base idle', and should be around the 550 rev/min area.

If the idle does drop when the hose is clamped, then the idle bypass ports are clear, if the engine stalls the idle bleed port in the throttle body is probable choked up with soot etc.

If the engine idles at anything other than 550 rev/min adjust base idle setting to achieve 550 using the plugged screw on top of the throttle body. DO NOT adjust the throttle linkage as the main throttle butterfly should be fully closed at idle ( another good point to check)

With base idle set to 550 rev/min release the hose clamp, engine revs should rise 1000 - 1500 rev/min and then slowly settle back to around the 650 mark, this proves the stepper motor is working, if there is no change in the base idle setting its usually soot and oil gunge in the throttle ports.

Second trick, I have seen the results of a poor gas setup where the engine has backfired into the plenum chamber and bent the throttle butterfly so that it no longer seats properly - worth a look while you are in the area.

HTH

Lofty

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Reply to
John Abbatt

I have a similar problem on my M reg 3.9 It does vary, some days runs perfectly, some days stalls at every junction, some days the rpm at idle will go to zero then shoot up then idle ok for a couple of seconds then zero etc.

On a typical day it will start up ok and run ok and idle ok until I have driven about a mile and half (just warmed up). When I stop the engine will die. Switching off the ignition and restarting solves the problem and it will be ok for the rest of the day (on a good day). I was wondering if maybe that was resetting something in the electronics to a default condition.

I have never cleaned the plenum chamber / idle bleed ports and will try following that advice, is it just a case of unbolting it and lifting it off? Am I likely to bugg** any thing up? or need a new gasket or anything before fiddling.

Would paying a dealer to run test book or whatever the expression is be a good idea and what is a typical price for them to do that?

Many thanks for all the advice.

Les

Reply to
Dadio

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