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Okay, so this is my first post here. I hope I'm doing it right and in the right spot and not offending anyone!! ;)
So I bought this beautiful 2005 Passat 1.8t Wagon earlier this spring from a friend of mine who runs a salvage yard. The car was hit pretty good in the left front so the intercooler and washer bottle, not to mention headlight, grille, and header panel (radiator support?) were wiped out. I took my time fixing it and today, took it out for it's maiden voyage and DOT inspection. I'm happy to say that it passed with flying colors! The Wisconsin State Patrol Trooper said he was very impressed with my repair work, and how nice of shape the car is in.
Let me just say that I am a big VW fan, however, I've never had a Passat, and I've never had a 1.8t. I own a MK4 Jetta with a 2.0/5-speed, and a MKV Jetta with a 2.5/Auto, that my daughter currently has at college. My point here is that I don't really know what to expect from this new car as far as performance is concerned. I am incredibly impressed with the ride quality as compared to a Jetta. It's much smoother and quieter and has a luxurious feel to it!
Anyway, here's what I'm getting from my maiden voyage: I noticed that when I'm going anywhere from 20-45 MPH and slightly accelerating, the engine seems to miss or jerk every second or so, maybe a bit more. It's a very quick shudder that is not hard at all to notice. If I give it a bit more pedal, maybe so the turbo spools up, there's no miss and it pulls just fine. At highway speeds, it's smooth as silk, even under acceleration, although it does feel a bit sluggish to me. (This is where I'm not sure if this is normal performance for a 1.8 Passat or not).
There is no CEL on but I did get a P0171 (System too Lean) and a pending P0234 (Turbo Overboost) code when I first started it. I put fresh, no ethanol gas in it because I thought maybe the one year old fuel in it was causing the CEL. Anyway, after resetting the codes and driving approximately 120 miles today, there were no lights on.
I ordered new NGK PFR6Q plugs today because I don't know if they have ever been replaced, so I'll see if that helps at all. I checked and double checked all my work and looked for vacuum leaks.
I'm hoping this is something that one of you Gurus here can easily diagnose.
Thanks in advance!!
 

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Thanks Ntrain2k. I'll have to make a boost leak tester. I ran a little Mapp gas around the vacuum hoses and didn't notice any change in idle. I don't know if that's a good way to check on this engine, but I read it somewhere and thought I'd try. The hoses all look perfect, so I guess I'm not surprised. The boost side of the system is a little different because I had it all apart, at least in the front and the intercooler. The large hoses, where they couple to the intercooler, seem loose to me. They don't come off but they move around quite a bit, so that's something to check out.
I changed the plugs today. If I had to guess, they were original. The gap was around .042-.046, they looked horrible, and they were all loose! The second plug back from the front had 1/2 inch of oil around it. Anyway, I discovered no change in performance with the new plugs on a short drive. I'm guessing my MPG might go up, but the miss/shudder is still very much there.
I'll be searching for a DIY boost leak tester on here next.
 

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From your description, I'd agree with Ntrain that you might have an air leak situation, which can cause that misfire, and possible lower boost too. Check the codes again to see if you have a lean-code pending. Part-throttle misfires usually are due to either an overy lean mixture, or weak spark. For certain, tighten all the induction hoses. If you don't see any indication of a lean mixture, then there's the possibility that a coil is marginal, or a bad coil connection, or ignition harness ground, etc, etc.

You mentioned the smooth ride and quietness; our 1.8T wagon was once my Wife's car (before the Touareg came along). It suffered a failed torque converter- which started as a shudder we couldn't figure out, so was out of commision while I located and had another transaxle installed. We bought a clean, low-mileage Honda Accord from an older couple, and she planned to sell the Passat once the transmission was fixed. A month or so later the Passat was back, and she had both to drive. The Honda was the car that my Wife sold (to my Sister), because the Passat was so much more comfortable and quiet.
 
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