Torque shop

My car, which has just passed its three-year warranty period, jerks rhythmically for several seconds every time I accelerate - especially from a low speed. I do not experience this while I am on the move and cruising or when I accelerate gently.

The jerking begins again if I want quick acceleration. I had the car serviced and the spark plugs replaced.There has been a slight improvement, but the jerking still occurs. I am worried that this could be a serious and costly engine problem.

The symptoms you describe appear to be caused by an ignition malfunction. This is commonly known as "misfire".

You did the right thing by replacing the spark plugs but, as you say, the problem persists, so your next course of action is to focus on the ignition components.

Get The Straits Times
newsletters in your inbox

For systems with remotely located ignition modules, the cables leading to the spark plugs should be replaced first as they are relatively inexpensive.

Many cars today have individual - meaning one for each spark plug - ignition modules or coil-packs. In this case, the electronic diagnosis would reveal the faulty ignition coil.

But it would be advisable to consider replacing all the individual units instead of just the faulty one. The fact that one is already about to fail suggests the possibility that it has reached the end of its lifespan.

In any case, the car will perform noticeably better if all the ignition coil or modules are replaced. This is not a serious or costly problem as long as you fix it soon.

SHREEJIT CHANGAROTH

A version of this article appeared in the print edition of The Straits Times on May 27, 2017, with the headline 'Torque shop'. Print Edition | Subscribe