HELP - Car shakes when idle & exhaust pops while cruising

[jackiechanclan]

Hi all - complete novice when it comes to cars so please bear with me.

I own a 2013 plate 2.0 litre petrol Scirocco R-Line with just over 60k miles from when I bought her brand new.
In the past couple of years, I've had problems with the catalytic converter light and EPC light coming on, but this was resolved by VW by having coil packs replaced.

Anyway fast forward to now / more recent times. In the last year or so the catalytic converter light has come on and gone off on it's own randomly for weeks at a time (EPC light not on). At times, the engine would shake upon fire up, starting every time but with a moment of slight hesitation to suggest it would cut out, but never did. The rev count would fluctuate around 1000 and eventually settle around 800/900 regardless of weather / temperature. At times, the exhaust would pop when cruising at 20 mph in 2nd or 3rd. I also noticed a slight delay in power when accelerating (not aggressively) with a slight judder.

I took it to a local independent garage and they (supposedly) replaced both lambda sensors before and after the catalytic converter. They told me that I'd need to give the car a proper run around on the motorway to expel any remaining O2, which I did. However, the problem persisted, the catalytic converter light came back on (again EPC light not on). And more recently upon fire up, I'd have to apply some gas in order for the engine to start properly otherwise it would cut out.

So I took it back to the same local independent garage to give them a second chance at diagnosing and fixing my car. This time they admitted that they had to contact VW for advice. The information relayed to them was to check the fuel injectors. So all four fuel injectors were replaced. Oil and filter changed in the process too. Upon driving the car away from the garage I didn't notice anything untoward until maybe 10 miles into my journey when I noticed that the exhaust would pop (again). I parked up at work and when I returned to my car some 6 hours later to go home, upon start up the engine would shake just like before, whereby applying gas would negate this. While driving, I could still hear my exhaust pop on occasion - no noticeable loss of power though.

Any help, ideas, suggestions, would be very much appreciated.

[Cuprabob]

I know you say the coilpacks were replaced relatively recently but it sounds very much like a misfire which would point to a faulty coilpack or plug. If it is misfiring then the fault code will be stored and should point to exactly which cylinder(s) is (are) misfiring which should point you or someone in the general direction. The reason the cat convertor light is coming on and the exhaust is popping is because there is unburnt fuel going down the exhaust due to the overfueling or misfire. To much unburnt fuel going down the exhaust will rist damage to the cat.

[jackiechanclan]

@Cuprabob - Thank you for sharing your knowledge and expertise on this. Not only for myself but for others who may be experiencing similar faults.
The first time I dropped my car off at the independent garage, my initial thoughts were faulty coil packs but that was purely based on my own very limited past experiences. I did mention this to the guy at the garage but he probably thought he knew better so perhaps didn't pay much attention to my prognosis. I'll be pissed off if this was the issue all along because I've spent the best part of £1k on things that probably didn't need changing. Obviously no harm done to the car by changing them but it's burnt a hole in my pocket for sure!
Are coil packs easy to source online and easy to replace? Are they simply plug and play?

[Gaz r]

If you can take the car back to the garage that haven’t resolved the problem. Ask them to complete a VCDS scan, if it shows a misfire error, then swap the coil pack over from a non misfiring cylinder and drive it and scan again. If the misfire changes cylinder, its most likely a coil pack fault. If not then check the spark plug/s on the misfiring cylinder/s.
I had 2 go on mine over the space of a couple of months, so the second time I just replaced all 3 so I knew where I was with them. They were about £40 each and are easy to change. Just be gentle and don’t force anything.
Good luck.

[jackiechanclan]

@Gaz r thanks for the advice. I think one of my mates has a VCDS so I'll ask to borrow it and check myself. If they're easy to change as well then I'll do that myself too. Not sure I trust this garage if they didn't do these seemingly basic checks first time around.

[jackiechanclan]

In the interest of closure for those who may have been following this thread and for those who may come across this in future with similar problems.

In short, changing the high pressure fuel pump (HPFP) seemed to fix the problem.

The guy who worked on my car (the final time) used VCDS and also took it for a test drive to try to diagnose the problem. Like me, he noticed that the exhaust would pop while cruising around town at low speeds BUT he also said that while giving the car a blast on the motorway or at relatively high speeds the car worked fine and the exhaust didn't pop, which I hadn't noticed because I daren't drive it that aggressively. Along with this test and having the car sat in his garage with the engine idling away, he noticed a fuel smell developing and mainly coming from the exhaust. This lead him to think that traces of fuel were slowly leaking into my oil hence why my exhaust would pop and the car showed signs of running rich. At low speeds the traces of excess fuel were not combusting but at higher speeds it was or was certainly less noticeable. After changing the HPFP, he took the car for a spin and it seemed to work fine. He also suggested that I change the oil and oil filter as they were contaminated.

Anyway that's as far as I understand about what was wrong and after about 6 weeks since fixing and oil change as suggested, my car hasn't had any more problems. I think I will change all 4 coil packs and spark plugs in the near future too. Thanks again for the community support and I hope this helps others with their car problems.

[eenbadendaap]

Glad to hear that you got it resolved and hope it won't happen again.

Enjoy your car !