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Discussion Starter · #1 ·
i have an 03 passat 1.8 turbo. lately it has been idling poorly, but the engine will run better at speed. it's lacking a little power, so i assume this is most likely a vacuum leak. i have spent considerable time trying to locate the leak and have been unable to do so. this problem started when the weather turned cold. one day last week we had a freak day where the temperature was around 70 degrees. my car ran great. acted as if absolutely nothing was wrong. the next day we were back to cold weather and my car was back to running rough. does this give any clue to the problem? anybody have any ideas?
 

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My car does the same thing, until it warms up. It then runs fine. I'm not sure why your car's behavior would differ in slightly varying temperatures while running at max temp. You should try installing a boost gauge, which is one extremely common mod that many people with the 1.8T have. It allows you to keep an eye on your vacuum level and boost, which of course will tell you if you have a problem in that department or not. If you don't want to install a boost gauge, there are a few tricks to checking for vacuum/boost leaks. Running propane gas around vacuum lines and looking for stutter, pressure testers, etc.
How many miles on the car? Does the RPM fluctuate a lot at idle? Does the car stutter at idle like it's going to stall? Do you have a check engine light?
 

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Discussion Starter · #3 ·
car has about 175,000 miles on it so i guess these types of things spring up. the engine does not surge at first. it idles at around 1200 rpm at start and will run fine, i'm guessing thanks to the secondary air pump. when it warms up and the engine idles down to around 800 rpm thats when it will surge and almost die. it always manages to catch itself though. the mil will flash when its surging. when you give it gas it will run smoother and the mil stops flashing (it stays on just solid) but the engine lacks power. you can go for miles but as soon as you stop at a light or something and get to idle the car will surge again. none of this happened when it was warm outside.
 

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Wow, thats really odd to me. Could be a clogged fuel filter or a fuel pump issue maybe...? If the fuel filter has not ever been changed, then you may want to do that.
The idle that starts at about 1200 and eventually decreases upon warmup to around 800 is normal. I'm not sure what the flashing CEL means in this case, but you're DEFINITELY going to want to have any codes or misfires read with a code scanner or diagnostic tool, ASAP. Autozone and AAMCO do free diagnostic scans, if you don't have a scanner. If you want to go get a scanner, it can be purchased at Advanced Auto or Auto Zone, etc., anywhere from $40-$120, depending on what features it has. But, anyway, someone else will chime in and can probably steer you more in the right direction with this issue. Just be patient :) Good luck.

Oh, if you have codes read and they just give you a Pxxxx number, here is a list of every DTC. http://www.passatworld.com/forums/showthread.php?t=150634

Post the codes up ASAP, and it will be much easier to diagnose a problem.
 

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Discussion Starter · #5 ·
codes are random misfires and system too lean bank 1. here is what i have tried.

cleaned throttle body
cleaned air filter and the whole air filter box
unplugged MAF to see if that made a difference, have not cleaned
replaced pre-cat o2 sensor
searched for a vacuum leak

fuel filter was changed about a year ago, along with spark plugs and ignition coils.
 

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Discussion Starter · #6 ·
also, i have vag-com if someone has any suggestion for thing to try.

forgot to mention i did a throttle body alignment with vagcom as well.
 

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Wow, I'm absolutely stumped then. Someone more knowledgeable will have to reply here. Haha

Edit: Actually, have you tried testing the fuel injectors and the fuel pump? The fuel pumps do go bad relatively quickly, and if it hasn't been touched since it rolled off the assembly line, I'd have a hunch on that. If it's running lean, then its obviously not getting the correct fuel required. Sometimes it takes me a few tries to read something and compute things in my brain. lol
 

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Discussion Starter · #8 ·
i was going to try testing the fuel rail pressure and go from there.....my uncle is a mechanic (completely unfamiliar with vw though) and he suggested fuel pump as well.
 

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Yes, definitely try that. I'm not sure what pressure is supposed to be going through the rails, so try a quick search with the google search bar at the bottom of the page. Most useful tool on this site besides the people on it.
 
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