Jerking when warm

POSTED BY CBT Team ON 30 July 2014

Legacy GT

I have a 1998 Subaru Legacy GT (manual) which lately has had some jerkiness on part throttle.

However, this only happens when restarting once the vehicle is up to temperature, i.e. after running for some time.

Cold starts first thing in the morning pose no such problems.

I drive this car daily; what could be the matter?

Brian Cheng

Reply: I would look at the ignition system first as there are two main possibilities:

1. The ignition cables, if they have not been replaced previously, may be cracked and there may be “crossfire” between cables, causing the jerking. Sometimes this may happen within the distributor cap.

2. One of the spark plugs is misfiring. On cold starts the air-fuel mixture is richer and usually the engine will start easily, but when the engine has warmed up, the mixture is leaner and a spark plug that is not up to the mark will misfire.