Surging.......

[Hedgehopper]

Was enjoying a run in the sun with Mrs. H yesterday thinking how well the car was going , when suddenly it started to surge and kangaroo. This happened at approx. 2000rpm and in all gears. It got so bad that the car was almost undriveable, eventually stalling when slowing to enter a roundabout. The engine wouldn't re-start. Fortunately I had recently fitted a battery master switch, which I then turned off for 30 secs or so, it re-started and ran perfectly for the rest of the journey home. This high frequency surging has happened several times before, always in the 2000rpm range, usually driving through towns at low speeds, but has in the past always cured itself as quickly as it started. The fault only seems to be related to engine speed. The stepper motor has recently been cleaned and plugs, dizzy cap and rotor arm are all less than 1500 miles old.

Has anyone any ideas what causes this and why does re-booting the ECU (by turning off the battery) cure it?

[paulathome]

Had this on the Chim and after many hours of investigation I found that the connections on the air flow meter were intermittent. As the cable boot was missing and had been replaced with black sealant I bought a new one with new crimps and cable boot for about 12 quid off Fleebay.
Since then no problems.
Paul.

[crackedfinger]

sounded like the problem I ha with the ignition amp, happens when it's hot?

[BigotOut]

Something definitely *switches* at 2000 RPM, I had that a while back, quite violent Went away of it's own accord but I'd be interested to know the cause.

[blitzracing]

The ECU does need some time at idle to set the overall mixture, and resetting it removes this setting, so it has to re trim again next time the engine idles. If you dont get this 20 or so seconds of idle time, the long term fuel trim does not get set correctly, and the ECU tries to keep the mixture correct with "short term " fuel trim, but this can cause bad snatching as it exceeds the limits the ECU has to adjust the mixture. I would suspect you have a combination of a bad sensor input causing a wrong fuel trim value to start with, BUT the ECU should always retrim at idle with or without an ECU reset.

[Hedgehopper]

Thanks everyone for your suggestions. First job will be to check and clean the sensor connections and then have the sensors themselves checked.

[aerospoke]

Had something very similar(exactly same symptoms). In my case it was the fuelpump or its connectors. Fitted a new one anyway. Problem cured!

Cheers Jens