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TQ: Over-revving automatic!

PaulHere

PaulHere

PCGB Member
Member
An owner has contacted me with a question about his 924 Lux 2.0 Automatic:

The car will drive perfectly all day, but suddenly the cars engine speed will suddenly 'stick' at 4,000 rpm and have to be held on the brakes and bought to a halt! Very worrying stuff.
The car will then cool down and drive normally.
I've had a look under the bonnet and everything seems normal, but something mechanical or heat related is making the car unpredictable.

Has anyone any suggestions, or experience of this problem.

Thanks William Burgess
 
Engine rpm that high can only really be air related. You might get 2,500 rpm from a shifting ignition advance curve. Air enters the engine via the throttle butterfly and the auxiliary air valve. It could be that the secondary butterfly is sticking open, because it is operated by a tab that runs in a slot. When the primary butterfly is closed the secondary relies on a spring to close it , and due to the slot it can still be partially open when the primary is hard against the stop. I would look there first, but being an auto there could be problem with the kickdown mechanism, or any vacuum feed to the unit; unfortunately I am not familiar with the idoisynchrosies of the auto 924 so I cannot advise further.
 
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