# Random misfires, especially after rain / wash



## reddie (Mar 28, 2015)

I've had a problem with a 2002 Bora (Jetta) with a 2.0l AZJ engine for about a year now. Random misfires that cause shaking, shuddering on idle, and in extreme cases nearly complete power loss and blinking CEL light. A good example of the problem was last weekend, when I took the car to an automatic wash. Going there, engine was running OK. But after the wash was finished and I started the car, blinking CEL and shuddering like never before. So clearly, the problem is related to moisture or humidity.

The steps taken so far: 
Took the car to shop nro 1, and they changed spark plugs and plug wires. On the way home I could already feel the misfires, and sure enough, CEL was blinking the next day. Took it back, they changed the plugs to better ones. Still the same problem.

Took the car to shop nro 2 (VW). They changed the ignition coil (2.0l only has one). Once again, on the way home, I could already feel the misfires, and verified with VAG-COM when I got home that indeed, random misfires on all cylinders but no fault codes yet. There were perhaps more misfires on cylinders 2 and 4 than on the other two.

The shop nro 1 used non-OEM parts, and of course, the VW shop said that the non-OEM plug wires could be to blame (which I doubt, as the problem was there before the wire change). VW measured the resistance of the wires and they were OK, but of course, the insulation might be insufficient. Nevertheless, I suppose changing the plugs and wires once again to OEM ones would not hurt (except my wallet).

Aside from the plugs, wires, and coil, what else could be causing symptoms like this on wet weather? Is there any reason that a vacuum leak would manifest only in wet conditions?

Fault codes: P0300 P0302 P0304


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## evanj (Jun 1, 2014)

I had similar problems for a long time, especially after a night of rain or damp weather, but new coils and wires stopped it 99.9%.

It still happens when it dips below -20F on a rare occasion.

My guess is water or moisture- as you suggested- perhaps in the gas.

Try a double dose of ISO-HEET in the tank and see if it helps. Make sure you get the right kind with isopropanol. 

This always works for me if it acts up on occasion. 

Check your fuel lines/filter too- maybe water is getting in somewhere.

report back.....


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## reddie (Mar 28, 2015)

Thanks for the great tip, evanj! I hadn't even considered water in the gas. We don't have the ISO-HEET brand here, but Red Line Water Remover & Anti-freeze seems like an equivalent product. Couldn't find info whether it contains isopropanol, though, and no idea what the effect on the injectors would be. Maybe have to mix it with Red Line SI-1 (a cleaner).


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## leastsignificantbit (Mar 31, 2014)

If it doesn't turn out to be the gas I would wait until it's dry and running fine. Then spray the coilpack with a small water bottle to try and induce the problem. Then try spraying other locations and see if that helps find the source.


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## atoson (Dec 29, 2002)

Moisture in and around the coil and spark plug area will cause this. 
Try wetting your motor while running, dowsing it with faucet water and see if it affects the operation.


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## Anony00GT (Mar 6, 2002)

Take a spray bottle and mist the crankshaft sensor while it's running. I've seen it cause these problems before.


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## reddie (Mar 28, 2015)

I still get some misfires, but I think now it's within acceptable limits (what's acceptable?? . No CEL so far, not even after rain, and the misfires are hardly noticeable. I suspect that the main problem was the coil pack, after all. The water remover and cleaner might have had some effect, but difficult to say. Thanks again guys for your help


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## atoson (Dec 29, 2002)

As Anony00GT suggested, use a spray bottle with water only this time spray around the coil area to see if any arching happens within. If it does, there might be a crack letting the electrical energy escape from the coil to the ground.


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## paul61 (Dec 6, 2011)

atoson said:


> As Anony00GT suggested, use a spray bottle with water only this time spray around the coil area to see if any arching happens within. If it does, there might be a crack letting the electrical energy escape from the coil to the ground.


Mine does it whenever it rains, without fail.
Spray coil pack, harness, and visible plug wires (with eng. running) with a good silicone based penetrant (hopefully something better than WD40?) , miss fire clears immediately.
The penetrant displaces water instantly. Anyone who remembers the points and a distributor days knows this trick!
Cheers


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## atoson (Dec 29, 2002)

If ever there is arching doing the moisture test, try looking for the source. It could be a hairline crack for example on a VR6 coil pack or a tear on the high tension cable, place silicone caulking (preferably clear bath tub 30 min dry time) on the crack itself. Caulking is a good insulator and doesn't conduct electricity while easily applied.


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## VWGolfer96 (Jun 16, 2015)

*Liquid Wrench*

You guys know how well Liquid Wrench Silicone spray works? And is it safe to spray while the engine is running?


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## dogdog (Jul 26, 2007)

seems to be a common issue on VWs... on fractured / cracked coil packs... lots of youtube videos on this as well.


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