Rough idle 1.2 azq 3 cylinder

[domleadenham]

Hi all,
im new to the forum but have posted a hi in the new members section.
Well where do I start....... I bought a 52 plate seat ibiza 1.2 3 cylinder azq last month with 52k on the clock with a fault. after about 10-15 minutes but then starts running lumpy on idle (fine up until this point) and sometimes cuts out. I've changed the ecu,clocks and key, still get the same problem.
My question is......
could it be that the timing chain has jumped a tooth or 2? (I know this is a common fault) But would this cause an intermittent rough running?
Thanks in advance and any help would be much appreciated

[Crasher]

Do a compression test, the symptom you describe is characteristic of a burnt exhaust valve due to worn valve guides which I have seen on this engine at as low as 29K miles.

[domleadenham]

Thanks crasher,
Wouldn't the problem be constant and intermittent though?

[Crasher]

It depends on how the engine ECU sees it. The random feeling comes for the ECU trying to prevent unburnt hydrocarbons from exiting the tailpipe due to incomplete cylinder combustion and the ECU can see this from crank speed between firing pulses and the oxygen levels before and after the catalytic converter using the dual lambda sensors and crank and cam speed/position sensors. if the ECU considers that high levels of hydrocarbons are being emitted, it will shut down the injector of the faulty cylinder and so you get a serious misfire instead of a mild lumpy feeling. I have seen countless people correctable detect this is happening via monitoring devises and go and fit a new ECU, harness, injector, coil pack and other parts before consulting someone in the know who tells them what is happening is a software protocol dictated by EU4 emissions laws.

[domleadenham]

Thanks crasher,
I've got a compression tester so I'll try that. Do you happen to know what psi i should be getting and what variance is acceptable? Thanks again

[Crasher]

It is all relative but 10 to 15 bar with no more than 3 bar between cylinders and no lower than 7 bar. On my Snap Off gauge, a good one comes out at around 15 bar with little variation.

[domleadenham]

Great stuff. I'll get that done before Thursday because m1tchy has kindly offered to come and scan it with his vagcom on Thursday too. Thanks crasher

[Crasher]

You can used VCDS as way to tell if the problem is likely to be compression. With the car misfiring badly, go into the fault codes and see which cylinder is the culprit, it will likely say random/multiple plus one specific cylinder and some other codes for lambda. Save/print these codes and with the engine still running and misfiring, clear the fault codes. If as you clear the codes the misfire disappears, you have my permission to swear profusely and kick the car.

[domleadenham]

I've done the compression test and all seems good with that. It's coming up on the vcds with fault angle sensor 1/2 but am I correct in thinking they're on the pedal and throttle body?? I've changed the throttle body and cleaned it out and also changed the pedal. I've performed a throttle body alignment too but still coming up with the same fault !
Here's what I've done so far
Checked the timing (ok)

Changed the cam sensor, crank sensor, speed sensor (gearbox)

Tried a different ecu, clocks and ignition barrel

And nothing seems to cure it!

I'm beginning to wonder if it's wiring between the pedal and throttle body

[Crasher]

Do you have the fault code numbers?