Throttle pot setting - lumpy idle

[duncscz]

Having searched a number of threads, cleaned stepper motor, reset ECU, changed plugs, changed air-filter (dizzy cap on order), I've still a lumpy idle. Came across this in one thread ...

... throttle pot on side of plenum. There are three (3) wires coming from this unit to a multi plug. Do not disconnect. Wire colors are Red, Green, Yellow. Red from volt meter to red wire of pot. Black wire from volt meter to Green of pot. Volts should read .33 to .35 volts if not, loosen the two (2) screws that hold it in position and turn it to get the correct voltage. If you cannot get the correct voltage setting, undo and remove the throttle pot, make the fixing holes elongated and you will be able to get the right voltage.

On my 2000 450, the (3) wires are coloured brown, green and blue !! Checking the voltage across them (brown - green) gives ~4.6V Adjusting the throttle pot reduces to ~4.5V ... nothing like 0.35V mentioned above.

Maybe ~4.5V is correct ? Anyone ideas ? Would the figure be ECU dependent ? If so, how do I know what ECU is fitted (as far as I know, it's 'standard').

[adyw]

Hi,
I had this last week on my Griff. The two issues I had were a lamba sensor defective and the throttle pot sensor setting reading 0.6v, Both meant the engine was getting over fueled in all ranges of the revs, Mine kept stalling on idle due to over fueling. It should be 0.3v, To make mine read 0.3v I had to enlarge the holes in the trottle sensor and twist it untill it read 0.3v at idle. So yes 0.3v is correct.

[GreenV8S]

Sounds as if you are measuring across the wrong wires. Two of the wires supply +5V and 0V to the pot, the third returns the signal voltage to the ECU. What you are trying to measure is the voltage between 0V and the signal. This will be around 0.3V with the throttle closed, and increase to around 5V as you open the throttle.

[duncscz]

Thanks GreenV8S .. you are correct. I decided to take the throttle pot off and make measurements .. all seemed ok off the car. I decided the middle pin was the 'wiper' and then measured that against earth .. got the right reading and so refitted and ok now. However, I guess the position is quite similar to how it was originally, so probably NOT the cause of the lumpy idle. Further searcing to be done ....

[blitzracing]

I think the latter 14cux's dont need the throttle pot adjusting, they crudely learn the voltage sweep. Id be suprised if you even have the holes elongated to allow adjustment. Check the output of your lambdas when hot (black and white wire), and check they switching between .3-.7 volts every half second or so. If one fails the tickover can get lumpy, although its hardly notaceble under load.

Mark

[GreenV8S]

Did you confirm that the throttle pot reading at idle was correct after refitting it?

I'd also suggest you confirm the coolant temp sender reading.

[duncscz]

Yes - throttle pot was ok - .35V at idle. Hopefully lambda sensors are ok (expensive!) - passed MOT recently. Will check coolant temp - upgraded rad recently fitted, so if anything, engine running cool (in 'current' climate).
Spark plugs were quite sooty (now changed). Engine seems to hunt between ~800 & ~1100 rpm at idle .. not really a problem .. just an annoying engine vibration/wobble while at traffic lights.

I also plan to check timing and verify actual idle speed ... which should be what? 800 rpm ?

Complicated stuff this ... my 3000S is so much simpler

[blitzracing]

Lambdas are dirt cheap if you know where to get them (about £14 each). Search for the Range Rover units. Takes a few days from the 'States. Who says we are being ripped off at £100 each ?? !!

http://stores.ebay.com/GLOBAL-AUTOMOTIVE