MY 2004 (round lights) VW Polo 1.4 16V runs fine when I drive it, but once I stop and take my foot off the accelerator, it drops its idling. I must then switch it off and start it again after a minute or so. A diagnostic test showed the engine was misfiring on cylinder number two. I’ve changed the cylinder head and coils, but the problem persists. What can it be? The wiring perhaps?
Arthur, the Polo’s behaviour shows some similarity to that of Brian’s Hyundai Accent, recently discussed in Car Clinic, but there are also significant differences. Most importantly, the Accent has a carburettor-and-distributor engine, whereas the Polo has a computer-controlled, fuel injection.
As luck would have it, my trusted adviser on all things Volkswagen recalled having had in his workshop a fortnight ago an identical 16-valve Polo with symptoms which were a carbon copy of yours.
He found (and not for the first time on those specific Polos) that at around 200 000km, the problem was in the wiring between the ECU and the injectors.
Start by examining the multiplug connecting these wires to the ECU. It should be free of corrosion on the contacts, and firmly attached. If the plug is good, you will have to get an auto-electrician to cut open the wiring harness along the run of the injector wires and look for a chafed or broken wire, focusing especially on the wire to injector number two.