GR Engine Misfiring at Low Revs & when Driving

[TANKMANIA]

Hi All, I recently bought my first FTO (semi-auto GR) and got a bit of a problem with the engine. It was running fine when I bought it and parked it up for 3 months because it needed two tyres. So i set about giving it a good clean. I degreased all the engine bay, disconnected the battery, sprayed contact cleaner on wiring harness plugs around the engine bay, took off the air box and cleaned out and refitted a brand new K&N. Sprayed contact cleaner on the air flow sensor and let it dry naturally. Took off the stepper motor and cleaned with WD40 and refitted (was running an erratic idle and since it cured the problem), took off the throttle body thoroughly cleaned out and refitted with new gasket sealer. Haven't touched anything else.

Started it up now and then but not driven it because it needed new tyres.

Recently started up and drove it. Immediately on low revs the car starts jerking, like a misfire, when given more gas the car is fine through the gears but the jerk is prominent at low revs. Nevertheless I took it for a spirited long drive to 'clear out' the system as I thought it was because the car was stood for a while. It made no difference.

I thought it may be the fuel filter so I changed it, but its made no difference. When I start the car (not driving) and rev it I can feel the engine 'missing' on low revs.

Since then its been parked up.. I've read about how to extract the diagnostic codes from the ECU but not tried that yet. (the guid was based on the mivec version).

I suspected the Ignition Failure Sensor may be faulty as the rev counter didn't work since I bought it, but would that have anything to do with the misfiring ? The misfiring didn't happen when I bought it.

Could it be the throttle position sensor as when I refitted the throttle body I put the sensor back roughly where it had been marked with white paint so I hoped it would be in its correct position.

Hope anyone can help..!

[Kace]

My bet is the Stepper. Clean it again and retry. Likely you will need to replace though as it will keep on happening.

[Mitsinut]

When was the last time the spark plugs were changed? Might be worth doing them. Was the fuel level low when you parked it up? petrol may be "dozed" from laying up for a while, rare, but can cause a problem. Are you sure all connections are sound, especially the ignition coils/module?