Seat Leon Cupra 1P Missfire on multiple cylinders/ idling

Apr 25, 2025
16
1
Hello, I have a little problem with my Cupra BWJ. I recognized that the car have a small missfire on idling and I have really no idea what can be wrong. I moved all ignition coils and spark plugs and still missfire on same cylinders. Just cylinder 2 is without any missfire. The most counting missfires are on cylinder 4 (about 10 per minute), 1 and 3 (about 2 per minute). The problem is just on idling. During acceleration and drive is everything OK. Compresion test was done and all cylinders are between 170-180 psi. PCV is new. Car has 220KW, R8 ignition coils, NGK sparks and so on. So there are some updates. What could be wrong? What should I check next?
 
Apr 25, 2025
16
1
I checked almost everything. You mean HPFP? I ordered new tappet which is inside the fuel pump. Also changed oil and filters, so I hope that filter is OK. How to check injectors? I was thinking that I can relocate injector from 4. to 2. cylinder and check if on VCDS if the missfires will change with probably "bad" injector. The car have good acceleration and the problem is just only on idling. Acceleration is smoth and without any vibration or strange noises. I'm going to replace new spark plugs tomorrow but I think that nothing will change.
 
May 13, 2025
4
0
Did you solve the problem? Have same issue after changing chains and belts.
Just misfiring on idle, accelerating all is fine, have about 220 kw too. Already changed PCV, fuel gas absorber, checked the coil plugs. After VCDS diagnostic, there is good fuel pressure in ramp, no corrections to fuel injectors. Found only one problem, that i don’t have data about correction for intake camshaft. Changed the sensor today, will plug VCDS later, problem is still here
 
Apr 25, 2025
16
1
No still nothing. I just found some damaged cables on MAF sensor. So I repaired the cables and cleaned the MAF sensor today, but it seams that maybe It is also not OK. Maybe I need to somehow reset the MAF values? I found that the values during driving jumps from cca 120-220g/s in full acceleration on 2-3 gear. So I don't know if it's because of the RESET is needed after cleaning and repairing the cables or the MAF is bad. I also found, that after I disconnected the socket from sensor, nothing much happened. Just idle is little bit different but the engine is still running quite well.
 
May 13, 2025
4
0
No still nothing. I just found some damaged cables on MAF sensor. So I repaired the cables and cleaned the MAF sensor today, but it seams that maybe It is also not OK. Maybe I need to somehow reset the MAF values? I found that the values during driving jumps from cca 120-220g/s in full acceleration on 2-3 gear. So I don't know if it's because of the RESET is needed after cleaning and repairing the cables or the MAF is bad. I also found, that after I disconnected the socket from sensor, nothing much happened. Just idle is little bit different but the engine is still running quite well.
Same situation, tried to change MAF sensor, nothing happened. Turbocharger works fine, so i don’t think it’s can be vacuum leak. PCV is okay too, after the data MAF is okey too. How i think, it’s can be the phase shifter, or when i changed it, i put the intake camshaft in wrong position, about one tooth. VCDS still don’t show me intake bank 1 in 93 group, and where is kinda like camshast system check in 94 group, test write that system not ok. Check maybe this too, because i don’t know where to check anymore.
 
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Apr 25, 2025
16
1
If you pull out the connector from MAF during iddling, does it change anything? I saw some videos on YT and found that the car should stop running after you unplugg the MAF. If it's still running after disconected MAF, it could be a BAD sensor or a small Vacuum leak.
 

James_R

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If you are happy that there is no cylinder leakage, I would do the following:

Take off the inlet manifold and check the back of the valves.
If they are full of carbon then have them walnut blasted clean.
Whilst the manifold is off and the injectors are easily removed, have them sent away, tested then clean/replace them as necessary.

Once it's rebuilt, have a see how it idles.
 
Apr 25, 2025
16
1
So today I found something else. I checked with VCDS the camshaft timing position and found that on level 93 - camshaft adaptation is -6 KW. What could be wrong? should I try at first replace the camshaft solenoid? Or the timing chain need to be replaced?
 
May 13, 2025
4
0
So today I found something else. I checked with VCDS the camshaft timing position and found that on level 93 - camshaft adaptation is -6 KW. What could be wrong? should I try at first replace the camshaft solenoid? Or the timing chain need to be replaced?
It’s time to change the camshaft chain and tensioner
 
Apr 25, 2025
16
1
it's enought to change only camshaft chain and tensioner? Because today in service they told me that I also need to change the timing belt and balance shaft and so on and they gave me price for all more then 1000€ for that... I just want to change what is really needed because the car drives well.
 
May 13, 2025
4
0
it's enought to change only camshaft chain and tensioner? Because today in service they told me that I also need to change the timing belt and balance shaft and so on and they gave me price for all more then 1000€ for that... I just want to change what is really needed because the car drives well.
I think it’s better to cut out balance shaft, after that the oil pressure will be better. I think to change the timing belt it’s will cost about 300-400€, it’s okay