I recently bought a 2006 GLI with 180k miles, 6sp manual. I dont know much about the vehicle history, but it does seem to have an aftermarket Hitachi HPFP, new gasket on the valve cover, PCV looks to have been replaced at some point, cone air intake (NOT CAI), and CAT delete with 3" downpipe. It is not running any tune that I know of.
- Shortly after I bought it, the car would jerk / buck during acceleration. Contacted previous owner, he said he had that a few times, but only after installing 3" downpipe.
- Ran Seafoam through the intake, and it seemed to help for a week or so. Plenty of boost and power. Ran great.
- Engine runs rough on cold starts. MIL flashes. After 45 seconds - 1 min, engine settles down.
- More recently, the engine runs good until it warms up. First 3-4 minutes of my drive every day its great.
- Once warmed up, it misfires like crazy. No power. No boost. Sounds like a Harley. Again, this is only once it gets to operating temp. MIL flashes.
- Codes P0300, P0301, P0303, P0304, P2293, P0010
- Cyl 4 is always misfiring. The other cylinders are random, but when it throws a code for misfire, cyl 4 will always be present.
- Fresh oil change (Mobile 1 0W-40)
- New HPFP cam follower (old follower didnt look bad, but its a cheap part. Inspected cam lobe and it appears fine)
- New MAF sensor
- New N80 purge valve
- New coolant temp sensor
- New N205 cam position sensor (havent got code P0010 since changing this)
- New NGK Iridium BKR7EIX plugs
- Coil packs are fairly new Duralast, but I bought a new one (also Duralast) for cyl 4 anyway
- Have swapped plugs and coils around in various configurations
I took it to a local Euro shop and paid them for a "diagnostics test". All they did was swap plugs and coils around and plug in an OBDII scanner (which I had already done) and tell me the codes. They said they didn't know what was wrong with it, but it could "possibly" be a bad injector on cyl 4. They offered to change all injectors for $1800. Won't take it there again.
I'm thinking it may be one, or combination of the following... maybe?
- Carbon buildup on intake valves
- O2 sensor
- PCV valve
- Diverter valve
- Possible other vacuum leak?
- Bad HPFP
- Bad LPFP sensor
Honestly, at the beginning it seemed like maybe a fuel issue, but now it really feels like a vacuum leak somewhere. Maybe both. I really don't want to pump a crap ton of money into this thing, as it has 180k miles. I just want the engine to run somewhat normal.
I don't have VCDS, and Im not sure if I can find anyone with it around here. I'm a little upset that I paid $100 to the Euro shop and they didn't even plug into VCDS. Might have to break down and get it. BTW, would OBDEleven give me the same data? It's half the price of VCDS.
OBDEleven would give you the same data to view. If you want to log you have to pay for the Pro version which is another $45 on top of the unit. Either way I think it's worth it, but that's my opinion.
Regarding the rest everything you said it could be, it could be. Symptoms you describe are similar to diverter valve failure but not the codes you're throwing. Also, don't think an O2 sensor failure would be as rough. I had one and all I got was a CEL and barely noticeable rougher engine, not what you're experiencing. I would start next with the fuel pressure sensor. Part Number: 06J906051D.
Low pressure fuel pumps seem to last forever but maybe the fuel filter is clogged or damaged. Part Number: 1K0201051K.
Then onto the high pressure fuel pump but hopefully you'll never get there. With so many of these engines swapping out the factory HPFP for a high performance one if you had a friend that had one laying around that could loan you to test that would be a bonus. I have one but I'm a bit too far (and in another country ).
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