Engine problem developing any ideas?

[phill 92]

My first problem with the 4age although I think it may be sensor related.

About 2 days ago I pulled up at some traffic lights and for some reason, I have no idea why, I slowly built up the revs whilst I was waiting (I was waiting a while and was very bored). Anyway I was building the revs to like 4k really slowly (like just resting my foot on the pedal) and the second time I done it I got to 2.5k and then suddenly the revs dropped of really quickly and before the needle could reach 1k it shot back up to where it was before. I was like oo what was that so tried it again and the revs built up as normal so tried again and it done it again. by this point the light was green and I drove off.

That night when I got home I popped the bonnet and done the same thing from the throttle body and the revs died randomly again and shot back up, tried it a few more times but couldn't get it to happen. I just left it as I thought I will never be able to diagnose it when its intermittent.

So today on the way back from work pulling off from a junction I floored it through the rev range went into second continued to pull through the rev range about 3-3.5k (I wasn't looking at the clock but that's what it felt like) there was a really violent loss in power for literally like a second just long enough for my body weight to move forward. Just as I had moved forward the power came back in as quick as it died I got pushed back into my chair.

This is the first time it has happened whilst moving but I thought I would get everyone's ideas before it develops into a problem.

Sorry for the short story but I thought I would give you all the details.

The engine is standard (I believe) and is a blue top, pretty sure it has MAF as there is a vacuum like on the intake arm running into a small black cylinder.

Anyone got any thoughts on this?

Cheers.

[Project D]

Have you checked your spark plugs ?

[jondee86]

phill 92 Wrote:About 2 days ago I pulled up at some traffic lights and for some reason, I
have no idea why, I slowly built up the revs whilst I was waiting (I was
waiting a while and was very bored). Anyway I was building the revs to
like 4k really slowly (like just resting my foot on the pedal) and the
second time I done it I got to 2.5k and then suddenly the revs dropped of
really quickly and before the needle could reach 1k it shot back up to
where it was before. I was like oo what was that so tried it again and the
revs built up as normal so tried again and it done it again. by this point
the light was green and I drove off.

This one definitely sounds like fuel cut. The throttle was so close to being
closed, that the ECU thought it was closed. High manifold vacuum, closed
throttle and revs above the threshold = fuel cut.

The other stumble will be something else.

Cheers... jondee86