Home Forums Hunting & Shooting Hunter's Campfire Hey mechanics - intermittent misfire at idle

Vehicle is a 2012 Jetta GLi - 2 liter turbo

I'm getting a P0301 code - misfire on cylinder 1

Only I never noticed it while driving. Just now however, after getting the code read and doing an oil change, sure enough it started idling rough.

Add some throttle, or get it under load and voila! Nice and smooth again.

This doesn't sound like coilpack or a plug issue to me, as generally don't those issues get worse under load?

Clogged injector maybe?

I'm thinking about swapping the coilpack from cyl 1 to a different cylinder to see if the problem moves with the pack.

Other thoughts?

Your going at it correctly.



Not always.



eliminate the plug the same way.

IAC valve

Plug and wire......

Calling Badger,calling Badger.

Try the cheapest thing first.

If you can zero the code and run it to see if it happens again.

I had a 97 dodge that had misfire codes and they had to replace the plugs in that cylinder two times before it quit.

Swapping parts is one way to find fault.

Never mind what I said just reread where it was a misfire on cyl 1

You don't say how old the plugs are but I'd start there.

A quick search brings up several threads about the same issue with people that have the same or close to the same model.

Well, it get's more interesting.

I just swapped coil packs between 1 and 2, then threw on a different reader.

The car is now idling and running just fine...

But now, instead of just a single code being read, there's a history of 7.

Looks like there's just a general 0300 code, as well as a couple 301s, 303s and 304s.

I cleared the history and will drive a bit more and see what happens.

Oh, and 55K on the odometer, so could be plugs, but I think coil packs are more likely. Now at 100K, plugs would be my first guess.

Try plugs first, wires second

I don't think I've had a plug go bad since I was riding around on a Kawasaki triple. Dig down through the codes. Bet its either an air leak somewhere, or the coil pack.

The car's computer is going 10011110011100111 instead of 11011110011100111. I hate it when that happens.

Scott,

Loosen the oil filler cap when the car is idling and see how easy it is to lift up off the valve cover. If it takes a lot of effort, then it's likely that the crankcase vent valve has a punctured diaphragm. This will cause a lean running condition, especially at idle, as the car is getting "unmetered air" from the crankcase. if you do find this to be the case, get it fixed pronto. The rear main seals on these engines are "bonded" to a metal carrier plate, and excess crankcase vacuum will suck that seal right off the plate. That's when it starts to get expensive.

You have the right Idea, switch high voltage parts one at a time to another cylinder
see what part makes problem go to other cylinder. Do easy cheap things first.
Change spark plugs. Clear computer drive 50 to 100 miles recheck codes. If
still have multiple codes check for vacuum leaks. Then check fuel pressure.
May need a better scantool after that. If car has 100K with original plugs
change plugs first.

Ignore Guntruck50 and listen to Badger, Badger knows German stuff.

I just knew he would see the signal.

Lifting the oil filler cap off took no real effort when idling, but right now the car is running flawlessly. 160 plus miles this evening and no new code. The engine does idle rougher when the cap is off, but didn't throw a code.

With the whole slew of codes occurring, it does seem like something more systemic than a single coil pack or plug. Can the crankcase vent valve fail by sticking ?

More likely a pin-hole in the rubber diaphragm of the valve, Scott. If you have a shop that can smoke test the crankcase, you'll know for sure. It may be in the early stages of failure. Typical lifespan of those valves is 70-110k miles, so you're in the ballpark. The O2 sensors can compensate for quite a lot, but sometimes, particularly at idle, they become overwhelmed and the lean run condition will create misfires. The ignition coils are definitely suspect and do fail often on these engines, and a simple test would be to swop the offending cylinder's coil with another and see if the misfire follows the coil. I suspect though, that you may have a vacuum leak, and the CCV is the prime suspect.

I'm hoping you're right, and it's not the main seal already. I did some more digging, and I think something is up with crankcase ventilation, as in the past few days, I'd get the occasional whiff of burnt oil.

So, VAICO brand? Are they the cheap Chinese knock-off, or the actual supplier to VW worldwide? If the former, I'll just pop for OEM. If the latter, why buy the parts that VW rebrands and sells at a premium?

Replace the intake breather hose at the same time?

Many thanks for all the help.

Regards,
Scott

Nope on Vaico. Chinese aftermarket. Use the OEM valve. Good idea to replace the breather hose too.