Stalling

[Taxi King]

My '96 Chimaera 4.0L has developed an annoying and pretty dangerous stall. After a fast motorway run she is stalling. As you come down the gears the revs drop often to stall or the revs go very low and then recover.

The stepper motor is new and the throttle potentiometer seems to have the correct Volts and Ohms readings.

From cold or easy driving the problem rarely but occassionally happens

Anyone got any ideas?

[Barreti]

Why did you replace the stepper and have you got the old one?
If the old one is still useable, put it back and see if it cures or changes the nature of the problem.

Beg or borrow another one if your old one was stuffed.

There is no guarantee a new part is serviceable so I'd always try to prove it rather than assume its new so the problem must be something else.

Thought of another thing for you, I have a stalling problem when I drive in really persistent wet conditions. I think its water getting into the road speed sensor but as I don't drive that much in horrible conditions I can live with it.

How long has it been doing it and have you been out in really wet weather?

Edited by Barreti on Thursday 18th November 12:42

[Taxi King]

The stepper motor was changed because the old one was cracked and sealed with PTFE tape. The fault was occuring with the old one as well and we changed it in the hope the new one would cure the problem. How unlucky can one get - a new part failing!!!

She has been out in very wet conditions, although yesterday was dry and bright. Ran her 20 miles at a steedy speed to my mechanic to do a oil change and another little job and she behaved perfectly. On the way back - with fresh oil 0-60 castrol edge I gave her some beans and the problem re-appeared.

[spend]

Spray plus gas all around, you may have an air leak, that will help you find it if so.

[Chimpafrolic]

I had exactly the same fault, in my experience it has nothing to do with the much maligned stepper motor.

In my case it was caused by a bad connection at the speedo.


SPEED GOVERNED IDLE CONTROL OPERATION EXPLAINED:

• The speed sensor mounted at the nose of the diff sends a pulse signal to the speedo

• The speedo reads the pulses and uses them to calculate & display the road speed on the dial

• The speedo sends a signal to a small box of tricks, lets call it the "ECU Speed Signal Unit"

• The "ECU Speed Signal Unit" turns the signal into something the ECU can read and passes it on to the ECU

• The ECU reads the speed signal and adjusts the idle as the speed drops to ensure the engine does not stall

So the problem is more than likely one of these four things listed in order of likelihood:

1) The speedo unit itself is not delivering a signal to the ECU Speed Signal Unit (this was my problem)

2) The speed sensor mounted to the nose of the diff is faulty or badly adjusted

3) The ECU Speed Signal Unit is faulty and not delivering a signal to the ECU

4) The ECU is faulty


As covered above my fault was caused by a bad connection at the back of the speedo so it was an easy fix and went like this:

1) Remove the dash top

2) Remove the speedo from the dash (there is enough loom to keep the wiring connected)

3) Check and clean all the wiring connections including the small white multi plug

4) Refit the speedo and dash top

5) Go for a drive and test the idle particularly after slowing quickly from fast cruising


If the problem remains the next step (because it costs nothing) is to re-boot the ECU, by following these steps:

• Ensure the ignition is turned off, and has been off for at least 5 minutes

• Disconnect the hinged connector at the ECU

• Reconnect after 2 minutes and test the idle operation as above

If you still have a problems the best cause of action would be to purchase one of these from Steve Heath:

https://delta.securesslhost.net/~shenglt/catalog/p...

The Steve Heath device will help you identify which of component is at fault, it also provides a better solution to the difficult to adjust TVR speed sensor fitted to the nose of the diff.

In summary:

• Ignore the stepper motor

• Systematically follow the steps above

• Test after each step

• Keep the faith

Good luck and let us all know how you get on.

Edited by Chimpafrolic on Thursday 18th November 19:26

[spend]

Block up the air pipe from the throttle to the stepper housing, I doubt if you will be able tell the difference once the engine is warm?

Cleaning out & adjusting the base idle air bypass & screw is likely to have more effect IMHO.

[blitzracing]

You may get a change in the airflow signal output after a run, as they get really cooked by the Exhaust manifold, much more than the Range Rover set up. This will make the engine mis fuel until the ECU can sort it out, and this takes a few seconds when the engine rpm can drop very low. You could try a heat shield of some sort as a test just to see.

[slideways]

I had a similar fault on my 4ltr found it to be a very badly worn cam,I hope yours is an easier fix

[Taxi King]

Many thanks to all who offered an opinion!

The problem turned out to be the base idle speed. It was set too low and was relying on the stepper motor to do all of the work. Now that the base idle speed has been increased the car is performing as one would expect.