Have an irritating throttle response problem with my V8 (with manual box) that has is proving a little difficult to track down...

Basically the engine hangs onto revs when changing gears , have gone through the obvious like sticking throttle and manifold vacuum leaks, response is the same on petrol & LPG.The strange thing is that it only does this above around 35 mph, below that the response is normal above that you release throttle & depress clutch and instead of the revs dying off there is a noticeable delay in the revs dropping so much so that gearchanging become jurky if you don't pause for a few seconds before releasing clutch.

I have a blackbox faultmate & this isn't showing up any obvious clues as to the cause of the problem, the only faults that occasionally come up are the fuel trims & have been advised that this is most likely due to the car being dual fuel and they go away again for a while after resetting the adaptive values.

In the last 6-12 months the following have been replaced with new OEM parts......

Air Flow Meter
Crankshaft Position Sensor
Both Coil Packs (after rough running & misfiring, cured that issue)
Throttle Body complete with throttle position sensor

Previously within the last few years I have replaced...

All hoses on the vacuum side including LPG, spark plugs with the reccomended Champion items plus a full set of Magnecor red leads.
Both head gaskets & associated manifold gaskets.

The only other item I can think of is the idle speed actuator so I have bitten the bullet & ordered a new one to eliminate that.
Have the feeling though that if it was at fault the response would poor at whatever speed not just above 35 and it would register a fault and not idle properly..
Other than the response issue the engine uses no excess coolant or oil and is smooth & pulls very well

Check tp see if there is a sensor on the cluch pedel. if it has it could be that. they put sensors on the clutch pedels so the ECU know your changing gear and in turn will stop you slipping the clutch and things like that

discopaul said:

Check tp see if there is a sensor on the cluch pedel. if it has it could be that. they put sensors on the clutch pedels so the ECU know your changing gear and in turn will stop you slipping the clutch and things like that

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had a look this arvo & can't see one on the clutch, just the brake...... good thought though, my works Vauxhall van has one to limit revs with clutch depressed.....

nothing on the clutch pedal!But mine does the same I jus
t assumed it was a emissions type thing to stop the engine slowing down too much,

throttle housing fault is it worse when warm? clean the housing and retry

vougese39 said:

throttle housing fault is it worse when warm? clean the housing and retry

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Throttle housing removed & inspected found to be clean, spindle seals look ok too.
Replaced idle control valve too, little better but not much.Tested for manifold leaks by pinching up bypass hose & engine stalled immediatly so I think it's ok on that score.
Seems about the same when warm or cold on petrol and LPG.

Just strange it does it above 35 mph, got me thinking it could be something to do with a speed signal into the engine ECU but speedo appears accurate & no faults present on SLABS or BCU.
Cruise control however has packed up, checked ususal hoses etc & all look ok, i know this relys on a speed signal so I wonder if the 2 issues could be related??