Hello , I have a Skoda Fabia 1.4 mpi, 8v, 2003, 68 bhp, with a pretty much mileage (198800), and the problem that I have is that at idle revs the revs dip slightly and rise back causing an engine shake which is quite annoying. I mention that I changed the timing chain, lambda probe and crankshaft sensor (as these were the main problems after I bought the car and I thought that the idle rev not stable and engine shaking is due to the faulty parts mentioned earlier). However, even after changing these parts, the problem persist, even if there are no fault errors on vag-com. The car has never stalled yet, even if it feels like when the idle rev dip and rise again and cause engine shaking. Also the fuel consumption is quite bad - 30 mpg in normal trafic (even if I read that the 1.4 mpi 8v engine is quite thirsty, but didn't imagine is that thirsty - with quite calm driving style). 

 

Also this happen mostly when the engine is warm.

 

Any ideas ? 

Coilpack breaking down when heated up causing a misfire?

Thanks for the advice, is there any method to test the coilpack (without testing with a new one ?). Also if this would cause misfire, then it shouldn't give an error like cylinder misfire or somethinf like this ?

If you take the plugs out and compare them you can sometimes tell that way if one cylinder isn't firing like it should. It may even be a spark plug. has it been serviced properly?

Edited 14 July, 20169 yr by SuperbTWM

The 1.4 mpi famously has a rough idle. What is your battery like? I ask because when my battery was in a poor condition it caused more load on the alternator which made the engine more lumpy at idle. It was much better after I fitted a new battery. It still has the typical mpi unstable idle though.

The revs are going a bit down when the engine fans are starting. The rpm drop might cause the car to shake a little. At least this is how mine is acting.

The spark plugs are ok, I checked them about 1 month ago, and about battery, I didn't think to check that till now. I'll check it and see the results...I don't mind slightly unstable idle, but engne shaking is annoying me (even if they are related)...and is not doing it every second....something like every 5-7 sec let's say...

What kind of petrol are you running on? Have you cleaned the throttle body ? Try some high octane fuel and give it a good run, keep the engine over 3000rpms for about 10-15miles. 

I'll try that, see how it goes..