# Misfire Help 2.8 30 valve



## 99mk3vr6 (Oct 19, 2004)

I did a search and am still not having any luck. I have a 1998 Audi A4 2.8Q that has a bad misfire problem. The CEL is on and flashes and has code P0300 (random misfire). The car has a new coil, plugs, wires, cam sensor's and ignition module and still misfires. Sometimes it gets to the point where the car barely runs. However I noticed that the car runs much better at freeway speeds and hardly ever misfires. But in stop and go traffic is really bad. Does anyone know what else it could be?
Thanks,
Cory


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## merrigan (Feb 3, 2008)

icm?


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## Slimjimmn (Apr 8, 2006)

*Re: (merrigan)*

have you replaced the fuel filter or pcv pipe hose yet?


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## 99mk3vr6 (Oct 19, 2004)

So I took it to a shop and i guy told me that the only reason its still misfiring is because it needs new catalytic converters. I'm planing to replace them tomorrow but i don't see how that can make the car misfire. Has anyone ever heard of this?


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## 99mk3vr6 (Oct 19, 2004)

*Re: Misfire Help 2.8 30 valve (99mk3vr6)*

Well guys i just did some testing and here is what i have. I changed the cats and still no luck. But i just realized that when i unplug the mass air flow sensor it runs the same, would that be a bad mass causing the misfire?
Thanks,
Cory


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## 99mk3vr6 (Oct 19, 2004)

bump


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## cafez (Jun 18, 2009)

*Re: Misfire Help 2.8 30 valve (99mk3vr6)*

Hi dude my 99 VW Passat 2.8L has the same misfire problem as you described. It runs smooth at highway but gets really shaky when driving at around 40mph, and when it's idle. The mechanics told me it's the coil pack and I ordered one from ebay. Will replace it in this week and see if that will fix it. Good luck.


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## spitpilot (Feb 14, 2000)

*Re: Misfire Help 2.8 30 valve (cafez)*


_Quote, originally posted by *cafez* »_Hi dude my 99 VW Passat 2.8L has the same misfire problem as you described. It runs smooth at highway but gets really shaky when driving at around 40mph, and when it's idle. The mechanics told me it's the coil pack and I ordered one from ebay. Will replace it in this week and see if that will fix it. Good luck.
 If you ordered it off ebay..good luck! I've had bad performance outa Chinese knockoff parts ..their QC is really poor..had dist cap that lasted a week or two B4 it burned thru..molding was so off center..hope your coil pack isn't Chinese!


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## tammers (Oct 30, 2009)

I am having a similar issue with my 03 Passat. Started misfiring/backfiring intermittently in the spring, and got worse. Mostly at idle and stop & go. Had it looked at, and was told it was coil pack. And cat on driver side bad. Replaced both. Started misfiring again, so changed spark plug in that cylinder and worked fine for a trip from Chicago-Detroit and a few more errands (about 750 miles) then started up again. Got progressively worse over the summer, until my husband decided to try fuel system cleaner. Worked much better for a few days - CEL even turned itself off for a brief time. Now I cannot drive it as it just idles roughly the minute we start it. 
Any suggestions? My husband works two jobs so I am trying to find him some more info to troubleshoot this with. Thanks!
03 Passat GLX - 30V/6cyl


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## tammers (Oct 30, 2009)

Forgot to mention last night that the first item changed was the mass airflow sensor (last fall).


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## MEDEL514 (Jan 12, 2002)

*Re: (tammers)*

Have you ran any compression tests on the motor? That would be another thing to check, as well as the vacuum system. If you have a vacuum leak this can cause all kinds of sensors to be off. And if you have low compression on one of the cylinders, you may only be running on 5 cylinders instead of 6 which would cause a rough engine at idle, but almost unnoticeable at speeds.


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## brilliantwagen (Mar 5, 2009)

I wonder if you and I are having the same problem. Are you able to get a vagcom and see which cylinders are misfiring?


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## matc (Apr 2, 2009)

*Re: (brilliantwagen)*

What type of spark plugs are you guys all running?


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## penet05 (Oct 22, 2009)

*Re: (matc)*

I tried to use Bosch 4303 +2 and my car started to misfire. Then went for NGK, now it runs smooth again.


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## dangerous_dave (Jun 28, 2006)

*Re:  (penet05)*

Change your mass air flow sensor. it could be due to front O2 sensors too.


_Modified by dangerous_dave at 8:02 PM 11-20-2009_


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## gizmocska (Jun 18, 2003)

*Re: Misfire Help 2.8 30 valve (99mk3vr6)*

Did you guys notice oil leaks around the spark pugs in any off these cases?Cause I just did the same tuneup repair as you guys and still miss fires....


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## DieGTi (Jun 19, 2001)

*Re: Misfire Help 2.8 30 valve (gizmocska)*

Phew! *Only a rich man trouble shoots by throwing parts at the car and hoping to get lucky.* Try the scientific method and get a Vag-com on the car to observe the misfire condition at idle. 
With the Vag-COM, observe "Measuring Blocks" 15 and 16. These blocks will show you the misfire count for each cylinder individually. It is quite common for a single cylinder to misfire and trip the multiple cylinder code. Watch for one cylinder counting more misfires than the others and focus your trouble shooting strategies in this area. 
A) If you have 1 cylinder counting more then begin by checking:
1) Compression (ask a mechanic to do this if you don't have tools)
2) Fuel injector (swap with low-misfire count cylinder, 5mm allen and flat head screw driver). If misfire follows the fuel injector to the good cylinder then fuel injector is faulty and should be replaced.
3) Spark plug (swap with new)
4) Spark plug wire (check resistance with multi-meter)
B) If all cylinders are counting misfire at about the same rate then begin observing the sensor values in measuring blocks 2-5 for out of spec conditions. 
1) The Ross-Tech software provides the spec values on the screen above the observed values. Note: *O2 sensor values will likely be out of spec as the RESULT of a failed sensor elsewhere in the system*. O2 sensors should be replaced only after all other sensors and conditions are verified within spec with symptoms persisting! 
2) Firing order - the cylinder numbers are identified on the valve covers near the spark plug holes with the plastic covers removed. The firing order of the coil is imprinted on the coilpack; check that the spark plug wires go to the correct cylinder.
3) MAF sensor - there is a recall open on this item for the large particle screen coming loose and lodging in the intake and/or throttle body. Check the screen and ensure the plastic retaining ring is salvaged from the part if you replace it. You will need to install this retaining ring on the new replacement MAF sensor.
C) If two cylinders are counting misfires at the same rate then focus on the coilpack. The nature of the design of the ignition system is such that two cylinders share a coil. The pairs are cylinder #3 and cyl #5 on one coil, cyl #2 and cyl #4 on the second coil and cyl #1 and cyl #6 on the third coil. The ignition control module is sealed and attached to the coilpack and servicing requires replacement of the entire coil pack.
1) If Cyl's #3 and #5 are misfiring together more than the rest then you likely have a bad coil or bad ignition control module.
2) If Cyl's #2 and #4 are misfiring together more than the rest then you likely have a bad coil or bad ignition control module.
3) If Cyl's #1 and #6 are misfiring together more than the rest then you likely have a bad coil or bad ignition control module.
Please pass this on to other people experiencing misfires and rough running conditions.


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## gizmocska (Jun 18, 2003)

*Re: Misfire Help 2.8 30 valve (DieGTi)*

Thanx a lot Andrew.


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## O_o (Nov 12, 2009)

*Re: (99mk3vr6)*


_Quote, originally posted by *99mk3vr6* »_So I took it to a shop and i guy told me that the only reason its still misfiring is because it needs new catalytic converters. I'm planing to replace them tomorrow but i don't see how that can make the car misfire. Has anyone ever heard of this? 

???
A misfire can ruin your cats, but I can't think of a way the opposite can be true. Besides, if your cats have had it, the ECU should throw an O2 sensor code.


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## 99mk3vr6 (Oct 19, 2004)

*Re: ()*

Sorry I haven't checked this thread in a long time. It turned out to be a faulty coil. The previous owner replaced it with a cheap Chinese one and I assumed it was good since it was new







I replaced it with a good used oem one and it solved the problem. So a lesson to all is to stay away from cheap non oem parts.


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## bobby97jettaglx (Jul 8, 2005)

*Re: (99mk3vr6)*

just fixed P300 error with new wires......


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## DeDe (Jan 30, 2009)

*Re: ()*


_Quote, originally posted by ** »_
???
A misfire can ruin your cats, but I can't think of a way the opposite can be true. Besides, if your cats have had it, the ECU should throw an O2 sensor code.

It was hard for me to believe it too but it proved to be true:
Once I replaced my clogged cat the misfire stopped. Same O2 sensors, same everything...
Remember this thread: http://forums.vwvortex.com/zerothread?id=4830319


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## O_o (Nov 12, 2009)

*Re: (DeDe)*

Yeah, I guess I was thinking 'used up', not 'bunged up', if I was thinking at all. A clog anywhere in the exhaust will make it run like sh!te. I'm sure we've all stuck a potato in somebody's tailpipe at some point in our misspent youths.







I got the impression however that the poor OP's mechanic saw codes and simply replaced whatever parts were mentioned. I'm also guessing he won't be going back to the guy that made him spend thousands on new cats that in all probability he didn't need...


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