Intermittent Running problem

[Emmdat]

I have just returned from a 1500 mile hoon around France taking my 400SE that incorporated a few days visiting relatives that live in the Auvergne region of France. Over all the car performed beautifully for the most part but developed an intermittent running problem over the last 500 miles or so.

It started after a fill up and started out as manifesting itself as what can only be described as kangaroo like tendencies in low gear slower speed running with only the loud peddle being engaged that necessitated changing up to keep the revs higher. Then when I took my foot off the loud peddle the revs didn’t fall away and approaching roundabouts or junctions generally when changing gear the engine would be screaming and running at what ever the last rev level reached had been! I could then get the revs to fall away by sitting at the stop junction in gear and keeping my foot on the brake would lift the clutch that caused the revs to fall away. When this happened I would then find myself in a fight to prevent the car from stalling! Sometimes when attempting to rev the car the engine wouldn’t rev and just sort of hold itself as if deciding whether to rev or to stall. There were occasional ‘Pops’ from the exhaust during this time whilst trying to rev at low speed or stationary. Then it would clear for half an hour and run without fault at junctions (or getting on and off the car ferry!!!)and then the symptoms would return! The car was unaffected at higher speed.

Any ideas as to where to start looking in an attempt to cure this?

[Wedg1e]

Sounds like the idle stabilisation valve (stepper motor) is sticking. It's on the back of the plenum chamber; unbolt, squirt full of carb cleaner, reassemble in reverse order

[rev-erend]

Either the stepper motor needs cleaning or.. there is an air leak into the plenum somewhere.

[Emmdat]

Thanks Guys. I did think air leak to start with and carried out a brief roadside inspection that didn't throw up anything obvious. I'll carry out a more detailed test as well as clean the stepper motor as suggested.

Again, thanks for your help.

[rev-erend]

Try clamping the air feed pipe to the stepper motor when the revs are doing their crazy thing .. if the revs drop when you clamp the pipe then you have found your culprit.

It's easier to eliminate the stepper than to find an air leek.