Cyl 1 misfire at idle only?

[rtm5003]

Hello all,

My car has been idling a bit rough lately - noting too bad, no CEL, but definitely noticeably rough if you pay attention.

I don't have VCDS, but do have a code scanner, which is showing misfires on cyl 1, but only at idle.

I took it to VW since I'm still under warranty and they told me they couldn't do anything since it wasn't throwing a code. They recommended fuel injector cleaning, TB cleaning, and Sea-Foam of the intake mani (at a cost of $420 lol.)

The misfire count for the other cylinders does increase to 1 or 2 per cylinder per driving cycle, but nothing like cyl 1.

Also note that while driving, the misfire count doesn't budge - the car is only misfiring at idle.


This is an 08.5 TSI GTI with 50k on it - APR stage 1, BSH recirc catch can... All four coils and plugs were changed with OEM parts at 45k.


So far, I've cleaned the MAF and IAT sensors (no change) and run a tank with Chevron Techron fuel system cleaner (maybe smoothed out the idle a little bit, but the problem is still there.)

I'm not sure where to go from here - could a dirty TB cause misfiring only at idle and only on one cylinder? How about a fuel filter? I just realized the recommended interval is 40k - I have one on order, but wouldn't any fuel problem other than injectors be across all cylinders???


Thanks in advance.


Edit: Vac/Boost levels are perfect and the car seems to be running 100% except for at idle.

[Jayj]

If it's actively misfiring then there is no reason for the dealer to shoo you away like that. Don't erase fault either, it resets fuel trims. I'd take it back and tell them to watch the misfire counters.

[shortydh]

Carbon buildup bro! Let the stealer ship do the work you will b happy or just pull the intake mani yourself and you will see

[rtm5003]

Right... My dealership, who has been great about covering stuff under warranty in the past, suggested that it could be carbon build up. Their proposed solution was a SeaFoam treatment @ $169.

They say without the computer throwing any codes, VW will not pay for any work.

He essentially told me to drive it until it throws a code.... Very helpful lol.

I guess I could pull the intake mani and give the intake valves a cleaning. But it does not sound like a fun job...

[Jayj]

It's easier than a fsi intake, that's for sure. It can be a bit tedious to pull the carbon out though.

[shortydh]

Agree! It's not too bad just prepare and if you do decide to do it make sure u get injector seal kits before u pull it

[rtm5003]

Agree! It's not too bad just prepare and if you do decide to do it make sure u get injector seal kits before u pull it

I figure it's probably a good idea to replace the injectors at the same time considering how much of a bitch they are to get to. I have heard a few rare cases of injectors on TSI's hanging open.


I guess we're somewhat lucky that we can give the valves a good cleaning by only removing the intake mani.......

[ViRtUaLheretic]

Seafoam is useless, especially for $100+ lol

Start simple and see if you can diagnose the issue from there.

Try swapping the coil in cyl 1 with the coil in cyl 3 and see if the misfire follows it.
If that doesnt do anything, pull all of your plugs and see how they are (verify gap too!).
Fuel filter will be a good thing, but I doubt that is the issue as well.

Double check all of the couplers and make sure everything is snug and not leaking.

P.S. you will **** your pants when you see how expensive our injectors are.

[shortydh]

Injector replacement ehhhh idk about that, it can get very pricey. The thing here is the dtc is coming at idle only . If it was a coil, the coil would cause a dtc at all times same goes to plugs and injectors.