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(Post Link) post #1 of 4 Old 30-08-06 Thread Starter
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Disappearing Revs - Please Help

MAF, Thermostat and Stepper Motor has been replaced. Lambda sensor was replaced but made no difference so the old one was put back. It has been on every diagnostic system and all resets have been done. Most problems have been solved with the erratic idling and lumpy drive. It drives MUCH better and is almost perfect.

One problem still exists and the mechanic admits that he does not know what is causing it.
When the car is in neutral and you rev the engine even though you keep your foot constant on the accelerator the revs will drop. So if you rev to 3000 the revs will drop to 2200 or 2000 and then slightly increase to 2500 (or there about). However this only happens if you suddenly press the accellerator. If you slowly increase revs then there is no drop. Where are the revs dissapearing to??????
I am taking it again next week to him so he can put it on the machine and see if any faults have come up to help pin point this mystery.

Whoever solves this problem gets a cold Guinness sent to him!
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Re: Disappearing Revs - Please Help

Could it be a air leak in the intake pipework??

It's a long shot but also check the OIL SEPARATOR VALVE. This is found behind the throttle body and connects a second crackcase breather pipe to the inlet manifold (not the obvious one you see connecting to the intake pipes). This is a plastic plunger on a spring and sometimes gets gummed up. If it sticks open, it lets too much air into the inlet and the revs alter. A good clean (or replace it, it's about £2.50!) might help. Take care though as the cover gets brittle and the small clip that holds it on the manifold breaks easily (hence the idea of a new one!).

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(Post Link) post #3 of 4 Old 01-09-06 Thread Starter
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Re: Disappearing Revs - Please Help

Anybody else with any suggestions? I take the car back to the mechanic next week and if nothing comes up well then I will just accept this problem and drive the car forever like this.
I am sure there is a simple explanation for this dropping of revs!!
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Re: Disappearing Revs - Please Help

Have you looked at the resistance that holds the butterfly closed? It may be that hitting the accelerator hard is causing the butterfly to open and its momentum, coupled with the sudden airflow changes is causing it to overshoot and then occilate breifly in the airflow until it settles to its proper position. This occilation would be compounded greatily by the airflow moving over the butterlfly as it woudl exagerrate the movements.

Admittedly its a long shot but it does sound possible that the butterfly is moving a bit too freely. Is the stepper motor fitted properly? Any chance you could slap another throttle body on briefly as a test?

Sorry, best I can come up with.
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