Hello, i have a skoda octavia 1.4 tsi chpa 140 ps 2015 on 205 000km. First owner. The car had no critical issues for all mileage.

Since February 2026 i have an issue with misfires on random cyliders. I check them with VCDS and OBD Eleven 3 on live data. Also total counter on cyliders is very different on cylinder 4 as: 1-26000; 2-27000; 3-30000 and 4-41000.

For certain trips the car generates up to 50 misfires mostly on cylinder 3 and 4, very less on others but still exists. There were a fault codes as P0300 and P0304.

I changed:

1) All 4 pcs. of injectors with new by Bosch.

2) Changed the coils from 1 to 4 and from 2 to 3 but no difference.

3) Sparks were also changed, no solution.

There are no errors as P0300 and P0304 after injectors change.

In the mornings, when air is cold 15 degrees misfires are less, than in hot wether as 30 degrees ambient temperature.

In the mornings during catalyc heating there is no issue.

When i turn on the AC the misfires gone and no misfires.

Without AC misfires exist.

Idle rpm are 719 rpm/min.

No issue with fuel preasure, injectors sealings, fuel rail, sensors, air filter. I checked the vacuum PCSV with oil cap opening, no issue seen.

On intake valves has less carbon on the valve tail. I didn`t do a hasenut cleaning.

Has somebody same or simmilar issue? How was solved? Why AC reflects to the misfires? The reason to solve this issue that i feel every misfire of engine. The shakings are very anoying.

You seem to have done all the sensible checks without success. AC on/off is an interesting clue. I think the A/C drive belt also drives the alternator; loading of the A/C will affect the belt flutter / tension characteristics so maybe the alternator or the tensioner need to be checked (as well as the belt itself). Good luck.

If it has direct fuel injection, it could be carbon buildup on the intake valves. My 1.2 TSI CBZB in a Mk2 Fabia also suffers from random misfires on cold starts, but they aren't picked up by VCDS. However, I'm planning to clean the intake valves soon.

In order to clean the valves, you can take different approaches (all of them require removing the intake manifold). For example, walnut blasting is probably the fastest and most efficient method. Another method, which VW used years ago, involves using a set of 5–6 zip ties and a drill to loosen the carbon buildup. Apply a suitable degreaser and let the zip ties remove the buildup through their rotation. You can then use a pick tool to remove any remaining residue.

Be sure to rotate the engine manually so that the valve is fully closed; otherwise, the carbon will fall into the combustion chamber, which isn't good.

I will try this method:

Edited 31 minutes ago31 min by Jack25