Polo Mis-fire and Lumpy Idle
 

My engine mis-fires when idling for a minute or two, but only when the engine is hot. If I stop and re-start the engine, it runs fine again for another minute or two before mis-firing again. When driving, the engine runs perfectly fine and does not feel sluggish or anything. There are no start-up issues either.


Looking at the rev counter, it seems to drop (not suddenly) to around 700 RPM when the mis-fire happens.


The diagnostics I had done on the engine confirms an intermittent mis-fire on cylinder three (but does not say what the cause of the fault is). I have had the coils and spark plugs replaced, timing checked and all the engine wiring tested. A compression test has also been done and rules out a burned valve.


Before I had the coils replaced, the diagnostics reported an intermittent mis-fire on all three cylinders. Since the coils were replaced, the mis-fire is on cylinder three only.


The mechanic now believes that the fault could be with the ECU. He said that a faulty coil (before I had them replaced) could have sent a charge back to the ECU, causing damage.


I am just after some advice really before I spend more money! Any ideas?