Rough Idle - Cylinder 2 Misfire only on Idle

[xillius200]

Hi,

Need some help diagnosing a Cylinder 2 misfire on a seat leon cupra 2010, tried the usual checking leads with multi-meter, swapping spark plugs and coils. Checked for vacuum leaks but couldn't see any, was a small amount of oil on spark plugs but nothing major, fitted a new valve cover gasket. The idle fluctuates around 720-760rpm engine load around 15% and a lot of misfires. The thing that has thrown me off is...if I remove the MAF sensor the car runs fine without a single misfire in cylinder 2. I even end up getting much better fuel economy. if I plug it back in it misfires, however if I turn on the AC, idle raises to 800rpm but not a single misfire either.

Running catch can, got rid of PCV
Fuel pump 5.13 bar
injection timing 0.77ms
MAF Sensor (G70) 2.4g/s on idle
Lambada Control (Sensor Voltages) - Specified 1.00 - actual fluctuates between 0.98 and 1.02
knock sensor test result - OK
Thermostat tes result - OK
idle regulator: -0.2%
idle stabilization self-adaption: -0.6%

hoping someone has some ideas with what could be causing it?? or could point me in the right direction

 

[Woody_72]

Have you read it for codes? What are the fuel trim figures like? At idle, an engine should use about 1 gram per litre per 500 RPM so your figures look right (assuming a two litre?) but that's not to say you don't have a weird MAF issue.

 

[xillius200]

Have you read it for codes? What are the fuel trim figures like? At idle, an engine should use about 1 gram per litre per 500 RPM so your figures look right (assuming a two litre?) but that's not to say you don't have a weird MAF issue.

Unfortunately read it for codes multiple times, nothing comes up. Using obdeleven scan tool, and yep it's a 2.0L I checked the Trim figures and the short term fuel trim bank 1 is -8% and fluctuating, long term looked fine around 13% as you say could be MAF, I have a friend with the same car, going to swap it on Saturday and see what happens.

Also don't know if this would affect it?? Camshaft adjustment intake b1 specified is 28.00kw, mines running 27.50kw with phase position bank 1 intake as -4.00

 

[Woody_72]

Yeah, I think that would be a good start, especially with no codes present. Odd fault though.

 

[xillius200]

Yeah, I think that would be a good start, especially with no codes present. Odd fault though.

thanks for the help annoyingly looking around a lot of 2.0 tfsi engines have had the same issue, but even more annoyingly some people haven't managed to fix it and others have had it happening from maps, throttle body's, injectors. It's a shame these cars are nice but a pain to diagnose when something goes wrong.

 

[Legojon]

You checked the cam follower recently? Could be an injector failing (or injector basket). There are a few places these days that will take your injectors out, test and clean them (or replace). I had mine done at R-tech.

 

[xillius200]

You checked the cam follower recently? Could be an injector failing (or injector basket). There are a few places these days that will take your injectors out, test and clean them (or replace). I had mine done at R-tech.

Replaced the cam follower recently, checked HPFP as well. Got a new intake manifold gasket on the way and some intake cleaner, so will be cleaning injectors and carbon build up next week, managed to source a spare injector (tested as fine) 2nd hand for 20, bit of a steal haha so may as well replace injector 2 at same time. Tried a different MAF as suggested has improved slightly but still not solved issue, thinking of cleaning lambda sensor as well just for precaution Will post up after it's all done

Also wondered if my leaking vacuum pump which needs a new seal (ordered) could cause an issue, like maybe a vacuum leak?

Random question, once I get this finished can't decide if I want to upgrade it or go for something with a 2.5 tfsi, just love the sound but also love this car. How is the stage 2+, currently just on a stage 1 from more-bhp, but car has done 141k now. Had it for 3 years, bought it with 66k, I've done a fair bit of driving.

 

[xillius200]

Thought i'd post back in case anyone else is having similar trouble or similar issues, in the end it was a leaky injector and also a mix of carbon buildup

After cleaning the carbon with a pick, wire brush, some carb cleaner and replacing the injector. Car runs good as new, thanks for all the previous replies.

PS: Yes I know I need to replace the hose to the vacuum pump

 

[Legojon]

Random question, once I get this finished can't decide if I want to upgrade it or go for something with a 2.5 tfsi, just love the sound but also love this car. How is the stage 2+, currently just on a stage 1 from more-bhp, but car has done 141k now. Had it for 3 years, bought it with 66k, I've done a fair bit of driving.

Must have missed this. Glad you got it sorted in the end. Stage 2+ is amazing. It still puts a smile on my face and upsets many an expensive car. 2+ is vastly more pull that Stage 1. I found Stage 2 a big disappointment. But also, I originally had Revo Stage 2+ and I had no issues with it and it was pulling 345lbs of torque. I swapped it for R-Tech 2+ and without any hardware upgrades, Niki got 427lbs out torque out of it - which is more than all my Revo stages added together.

Aside from that, he also mapped the traction control. Which at first I hated LOL. Till I figured out how to use it and now I love it! The morale of the story is, if I was to do it all over again, I'd skip Stage 2 and go straight for a Custom 2+.

 

[ash_89]

Mine was a duff injector as well @xillius200 glad you got it sorted ... also
stage 2+ as @Legojon says is killer the torque just keeps pulling and pulling recommend r-tech in Nuneaton all the way .

 

[xillius200]

Mine was a duff injector as well @xillius200 glad you got it sorted ... also
stage 2+ as @Legojon says is killer the torque just keeps pulling and pulling recommend r-tech in Nuneaton all the way .

thanks I have heard nothing but good things about r-tech will have to take a trip down there in near future

 

[ARO]

Thought i'd post back in case anyone else is having similar trouble or similar issues, in the end it was a leaky injector and also a mix of carbon buildup

View attachment 18635 View attachment 18636 View attachment 18637 View attachment 18638

After cleaning the carbon with a pick, wire brush, some carb cleaner and replacing the injector. Car runs good as new, thanks for all the previous replies.

PS: Yes I know I need to replace the hose to the vacuum pump

Thanks for much for posting this, I have exactly the same fault on the cylinder 2! 120k on my 11 plate Cupra, I have ordered new plug/coils as they were ruined in 3 months by water through the bonnet! I've now sealed that, however tried an old spark and coil and still misfire, going to try the above next week, gives me hope that I can fix it!

 

[xillius200]

Thanks for much for posting this, I have exactly the same fault on the cylinder 2! 120k on my 11 plate Cupra, I have ordered new plug/coils as they were ruined in 3 months by water through the bonnet! I've now sealed that, however tried an old spark and coil and still misfire, going to try the above next week, gives me hope that I can fix it!

Did you end up managing to fix it in the end?

 

[ARO]

Did you end up managing to fix it in the end?

No unfortunately, I think it was the cam chain, which I replaced but had to drill out the VVT cog bolt, renewed it and I'm positive I got the timing spot on, tested a few times by hand but for some unknown reason the VVT pulley disintegrated after 5 mins of running and has destroyed the engine, deciding where to go from here.