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Re-acuring Check Engine light problem

I am having an issue with a check engine light that keeps popping up. When it first appeared the fault code was for misfire in cylinder 4. I took the opportunity to change all the spark plugs with factory NGK and all ignition coils with VW coils. I had the engine fault codes erased. It has been two weeks and engine was running great, but in the last few days it has been idling rough and the check engine light came on again. The rough idling happens at about 1100 rpm and u can feel vibrations in the car. I had the code checked again and it said misfire in cylinder 4. Anyone have thoughts on what this could potentially be??
 

GolNat

Autocross Champion
How many miles are on it? Has it had a carbon cleaning? Did you check the gaps on the plugs? I know they come pre gaped but one of mine was off.
 

JW with a VW

Go Kart Newbie
I know it sounds simple, but also check to make sure where the harness connects to the coil pack is secure. If the little clip is missing or broken, it may be causing a bad connection...just a thought.
 

zrickety

The Fixer
Yeah I would think it's a fuel injector. Try some injector cleaner with a tank of top tier (Shell 93 or similar).
Drive it hard for 30 min (3000+ rpm).
Let us know how it goes.
 

GolNat

Autocross Champion

JW with a VW

Go Kart Newbie
I will check the connections and try a fuel injector cleaner and see how it goes. Any recommendations on which injector cleaner to use?
I use Chevron Techron Complete Fuel System. Highly rated and avail at most auto part stores.
 
I have been driving with the fuel system cleaner for about 4 days and not seeing any improvement. My check engine light is still on. When I checked the connections they were connected all the way up the end of the ignition coil. But I noticed that I could slide them off with out having to push the clip. Could this be the issue? They need to click into place. My EPC light came on for a min when I started it up yesterday. Then shut off as I started driving. Any other suggestions ?
 

GolNat

Autocross Champion
Did you clear the code when you put the bottle in?
Yes they should clip into place.
 

JW with a VW

Go Kart Newbie
Could be a bad coil pack still...you can try swapping number one and number four pack, clear the code and drive it for a bit. If the code changes to that cylinder, then you have found the issue.
 

jedred1

jedred1
^^^^this is how I found my bad coil. i switched coils 1 and 2 and cleared the code. One week later CEL came back but this time said cylinder 2 misfire so I just changed my red coil packs back to the original black ones and no CEL’s yet^^^. I also replaced my spark plugs but don’t think that was the issue. It was just time. Good luck
 
Last edited:
after much trial and error. I replaced coils, spark plugs, cleared codes, used injector cleaner, and tested each individual cylinder. I took it to a local German Auto tuning shop and had them take a look at it and it was carbon build up. Had them do a walnut blast to clean out all the carbon build up. This completed changed the drive of my car, drives like a new car. It was built up pretty bad. All check engine lights are gone and drives like a dream
 

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GolNat

Autocross Champion
Whoa!! Yeah that was bad. Glad it's all better now.
 
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