Misfire? No CEL or symptoms..

[macq]

After about two hours of driving I parked the car on saturday afternoon on a very slight incline, enough steep so the car rolls back very slowly when in neutral. Not my normal parking sopt. During the night the temps dropped down to about ~11 deg from ~20 during the day.

The next day temp went up to ~30, and around noon I went to fire her up. Took longer than usuall to get her going and immediately the engine reved up to about 2k and dropped down way below 1k shaking violently and choking, finally it died. Fired her up again, same thing, but this time it will bounce between below 1k to above 2k trying to keep revs and not dying again. Looked at the boost gauge and it way bouncing from ~22 in Hg to ~10 in Hg. Died again. Third time it got somewhat better, but the engine was still shaking, revs slightly above 1k, 10 in Hg. Sounded like it was runnig only on 2 cylinders or so, basically missfiring a lot. No CEL throughout the entire happening.

Had to go somewhere and took my brothers car. About two hours after that I fired her up again, no problems. I let it sit to warm up a bit, and took it for a spin, no issues. Floored it a couple of times, no issues, normal boost. Wtf?

Today no issues at all, but while idling when I rev it up to over 1.5k it backfires more than usuall.

One day before, on friday, I filled her up at different station, still at Shell. Im at almost 62k, APR Stg 2 93 oct, intake, catless dp. Changed cam follower last summer and plugs about year and a half ago, at ~40k IIRC (stock Bosch), didnt touch pcv or coil packs.

I red a couple threads about misfires and similar issues, and want to make sure Im troubleshooting correctly.
-bad gas (?)
-bad coil pack(s)
-bad plugs
-clogged injector(s)
-carbon buildup
-temp(???)
-???

Sorry for the essay

Any thoughts and help would be appreciated, thanks.

 

[macq]

Anybody knows what could cause this?

 

[The Fed]

PCV? No CEL? Did you scan for random misfires? Not eveything trips the CEL.

 

[macq]

PCV? No CEL? Did you scan for random misfires? Not eveything trips the CEL.

I dont have vag-com or any other OBD scanner..

How would bad PCV have anything to do with misfires?

 

[The Fed]

Frankly, I don't know, but the dealer just replaced mine, along with a bad coil pack, and my misfires are gone. I was getting codes for the bad coil pack, and random misfires in 3 cylinders. I think if the PCV is leaking, it might run lean, because logs showed my injectors pulsing open too much. Someone else with more knowledge will need to verify or dispute what I say. You need to get someone with a VAG-COM to do logs to get a better idea of what's wrong, or take it to the dealer. What year is your car?

 

[macq]

Frankly, I don't know, but the dealer just replaced mine, along with a bad coil pack, and my misfires are gone. I was getting codes for the bad coil pack, and random misfires in 3 cylinders. I think if the PCV is leaking, it might run lean, because logs showed my injectors pulsing open too much. Someone else with more knowledge will need to verify or dispute what I say. You need to get someone with a VAG-COM to do logs to get a better idea of what's wrong, or take it to the dealer. What year is your car?

Thanks for the input. Its '07

 

[The Fed]

So is mine. I have 37K miles, still original plugs but I'll change them at 40. And dealer said when you snap your foot off the gas pedal it stresses the PCV.

 

[SpoonGTi]

for anyone that a Mk5 that's not stock. I would highly reconmend on getting a vag-com. Other than that, check the plugs and see if they have any oil on them. Or the coilpacks might have to be replaced to the lastest rev. I'm running the NGK Iridiums which is a colder plug along with the lastest coilpack rev.

 

[alphabits]

Rough idle and misfires on cold starts are usually carbon related. I had that happen to me on just Stage 1. My dealer had this induction service where they sprayed GM top end cleaner into my vacuum. I get misfires every so often still, but my car starts like a champ in the cold now and the misfires are no where near as bad as they were. I plan on going in for another treatment since it was only like 80 bucks.

 

[macq]

So is mine. I have 37K miles, still original plugs but I'll change them at 40. And dealer said when you snap your foot off the gas pedal it stresses the PCV.

Hmm interesting, so when the revs drop rapidly the pressure under the valve cover raises? Sounds somewhat believalbe.

for anyone that a Mk5 that's not stock. I would highly reconmend on getting a vag-com. Other than that, check the plugs and see if they have any oil on them. Or the coilpacks might have to be replaced to the lastest rev. I'm running the NGK Iridiums which is a colder plug along with the lastest coilpack rev.

Ahh didnt think about that, will check the plugs tomorrow, and vag-com is on my to get list. Also, I already have a set of NGK Iridiums, come summer and I will be changing them, as well as checking out several other things, follower ect.

Rough idle and misfires on cold starts are usually carbon related. I had that happen to me on just Stage 1. My dealer had this induction service where they sprayed GM top end cleaner into my vacuum. I get misfires every so often still, but my car starts like a champ in the cold now and the misfires are no where near as bad as they were. I plan on going in for another treatment since it was only like 80 bucks.

Didn't know dealers could have some sort of treatment for carbon buildup. I'll check if my dealer doesn't offer something like this too.
Actually carbon buildup was on the list of causes.

Thanks for the help all.