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Random misfire

Tiny
JETMAN11
  • MEMBER
  • 2005 VOLKSWAGEN PASSAT
  • 1.8L
  • 4 CYL
  • TURBO
  • FWD
  • AUTOMATIC
  • 112,000 MILES
I get 9 codes for misfires and random misfires, What I have checked and replaced: checked for vacuum leaks and replaced related tees and fittings, I have sprayed carb cleaner at and round hoses and tees with no change in engine rpm, replaced with new plugs and coils, checked all connections for corrosion, sprayed with contact cleaned, cleaned MAF, unplugged the maf while running with no change, the engine starts and runs every-time however has a constant random misfire mostly while idling however when I bring the rpm up to approx. 3000 rpm it seams better but searches when I hold the throttle in one position. I have done the wire check such as wiggle while the engine is running with no apparent change, I've done so much that I forget what I've checked already. Any ideas?
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Friday, April 24th, 2015 AT 5:11 AM

10 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
The pcvs leak vacuum and cause a lot of issues and codes pretty common.What are the exact code numbers not code descriptions do you have?

This code can help

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

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Sunday, April 26th, 2015 AT 8:44 AM
Tiny
JETMAN11
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  • 5 POSTS
Well. The codes that I had were P0300-304 and P0351-354 however I removed the new aftermarket coils that I purchased from e-bay and I installed 4 known good used coils and the p0351-354 went away. But it is still misfiring. I re-installed another set of spark plugs, still the same problems. I checked a multitude of different ways for vacuum leaks however I never smoked the vac. System. I changed the PCV a second time with no change. I did clamped all the vacuum ports on the intake manifold; still no change. This is how I isolated vacuum leaks before. It sounds like I'm getting an ignition crossfire except when I bring the rpm up to 2000 and above and the engine runs fairly well; it appear not to be cross firing anymore. The power in the engine does not seem significant.
I'm attributing the codes P0351-P0354 to the ebay new coils. I've never heard of this happening.
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Monday, April 27th, 2015 AT 6:36 PM
Tiny
JETMAN11
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  • 5 POSTS
BTW the used coils were oem
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Monday, April 27th, 2015 AT 6:39 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
If you clear the codes do the missfire codes come right back at idle?If so if you clear the codes while holding the rpms at 2000 do the codes come back?The best way to check for vacuum leaks is to smoke it.I made my own smoke machine since there so expensive it works great.
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Monday, April 27th, 2015 AT 8:53 PM
Tiny
JETMAN11
  • MEMBER
  • 5 POSTS
Great point. I know the check engine light will not illuminate however I will check again to verify. I believe they do come back as pending only while driving.
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Tuesday, April 28th, 2015 AT 7:42 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Let me know what you find.
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Tuesday, April 28th, 2015 AT 6:36 PM
Tiny
JETMAN11
  • MEMBER
  • 5 POSTS
I cleared the codes, ran the engine too 2000 rpm and no codes came back
however. The rpm wavered approximately from 2000 to 3000 rpm. When I let
it idle, the codes came back and the wavering stopped.
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Thursday, April 30th, 2015 AT 9:56 AM
Tiny
JETMAN11
  • MEMBER
  • 5 POSTS
I cleared the codes, ran the engine too 2000 rpm and no codes came back
however. The rpm wavered approximately from 2000 to 3000 rpm. When I let it idle, the codes came back and the wavering stopped. The check engine light is on with the same 5 misfire codes with an additional P0171 bank 1 lean code. Also i've been monitoring the STFT and LTFT the long term shows lean 25 at cruising speeds along with a lean 25 however I press on the throttle and the STFT starts to go to -8 to -20.I no what your thinking is it's a vacuum leak however when I block all the vacuum ports, nothing changes.
Frustrating!
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Friday, May 1st, 2015 AT 11:07 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
I see you just cleaned the MAF most of the time this does not work you need to replace it

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

Please let us know what happens.

Cheers
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Friday, May 1st, 2015 AT 12:16 PM
Tiny
JETMAN11
  • MEMBER
  • 5 POSTS
That did it, I got a new one from Amazon the car has never ran better! Thank you so much I love this site.
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Tuesday, May 5th, 2015 AT 12:06 PM

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