Engine revs Cycle up and down 200rpm, Help please.
16 January 2012, 10:55 PM
#1
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Engine revs Cycle up and down 200rpm, Help please.
I've developed an issue,
The car runs fine other than between 2000rpm and 3000rpm, it feels like its misfiring / Stumbling, however when i sit still and hold the revs above tickover, the engine cycles up and down 200 rpm at what ever rev range, ive changed the plugs replaced the fpr, swoped the MAF with one that we think is ok. logged the 02 sensor thats showing a signal.
the cars been fine for a long time but has now developed the fault, its running 20% meths, rotated inlet, FMIC, equal length headers (rescently fitted) full decat.
im a bit at my whitts end, any help would be great.
The car runs fine other than between 2000rpm and 3000rpm, it feels like its misfiring / Stumbling, however when i sit still and hold the revs above tickover, the engine cycles up and down 200 rpm at what ever rev range, ive changed the plugs replaced the fpr, swoped the MAF with one that we think is ok. logged the 02 sensor thats showing a signal.
the cars been fine for a long time but has now developed the fault, its running 20% meths, rotated inlet, FMIC, equal length headers (rescently fitted) full decat.
im a bit at my whitts end, any help would be great.
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21 January 2012, 01:45 PM
#8
With the engine ticking over,have a careful spray around your induction hose connections,inlet manifold etc with some WD40 or similar - if you have an air leak anywhere,the revs should increase as the WD is drawn in and burnt.
Failing that,any fault codes stored in the ECU ??
Mick
Failing that,any fault codes stored in the ECU ??
Mick
22 January 2012, 02:11 AM
#9
As above: Inability to hold steady fast-idle revs is classic sign of inaccurate air mass reading which is causing the ECU to constantly trim the AFR via the OS sensor (which switches between rich and lean once every second causing the revs to fluctuate: so weak, revs rise, rich, revs drop, weak revs rise, rich, revs drop).
Two things cause usually that....VACUUM LEAK or the second hand MAF is also buggered.
A smoke tester is ideal for this; We have one and its been a god send for finding leaks in hard to see places....just follow the smoke trail!
Last time I used WD40 on a car trying to find inlet manifold leaks, it got too close to a dodgy HT lead and went boom! (something to consider if you have a manifold mounted coil pack)
Two things cause usually that....VACUUM LEAK or the second hand MAF is also buggered.
A smoke tester is ideal for this; We have one and its been a god send for finding leaks in hard to see places....just follow the smoke trail!
Last time I used WD40 on a car trying to find inlet manifold leaks, it got too close to a dodgy HT lead and went boom! (something to consider if you have a manifold mounted coil pack)
Last edited by ALi-B; 22 January 2012 at 02:20 AM.
22 January 2012, 07:12 AM
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thanks for the feedback guys, ive sprayed with brake cleaner but nothing changes i can hold the throttle at 2k or even 3k with the same effect, how do i go about the smoke idea, and links.
Im going to try the MAF of a mates car aswell.
Im going to try the MAF of a mates car aswell.
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