Thinking of buying 2006 pasat 2.0 turbo 70000 miles when i pull of oil fill cap it startes to run rough and when i put it back i boggs down then runs normall again is this something to worry about?

3.8L V6, (from old 3.3l ) OHV ,push rod simple )
same car as one of mine, same engine, mine is 08
p0300 means all 6 cylinders fail or combustion pressure, weak.
at random.
so not 6 bad spark plugs news and gaped to speck
so is bad fuel?
so is 6 clogged injectors,, NO.
hot engine has normal idle rpm 800 or screams only.
yes that is called gross misfire and lost of engine power too you forgot to say.
got AF radiator water in the oil pan , looks like like chocolate milk?
mine has 100k runs like new, water pump only failure ever, 100k miles me.
seems like bad fuel to me. ,diesel put in to gasoline tank?
the only weakness this motor I know is 2.
1:lower manifold gasket leaks and AF coolant falls to top of engine and down.
replace coolant every 5years is win to avoid that.
2: egr failure sticking open and a pain to reach, unless right finder pulled fully
im sure compression tests pass at 150psi up. sure. 50k miles how can it fail.?

make sure at AM dead cold engine, rad cap off rad neck is 100% full of AF.
never let it drop, and keep side tank 1/2 full cold.

never forget to burp the coolant here as you replace it all

as you fill it up.(AF antifreeze coolant)
hose off here, heater)
fill rad until it leaks here
hose back
then fill rad full to top of neck.




https://drive.proton.me/urls/2AJBWHFE3R#n9DXuC8sIcOD

link is new pump installed steps PDF

If it is running rough & no check engine light on then the first thing I would to is tune it up. If you have a check engine light then pay someone to diagnosis it & go from there. Usually when the light comes on there is a more promenient issue; that is WHY the light continues to flash.

General rules of thumb: Low speed engine on acceleration with smoke in the exhaust plume = worn piston rings High speed engine accelerating (spooled up turbo) with smoke = oil form turbo bearing and/or piston rings Engine on over run (coasting down, foot off the gas) with smoke = oil from valve guides. VW/Audi make good engines with tight tolerances so none of the above should apply at 62K miles; just make sure that the oil (the right oil) and oil filter are changed regularly.

Fluid Level Checking & Filling To Check:

1. Connect a scan tool to the vehicle to read ATF temperature. ATF checking temperature should be 95° - 113°F (35° - 45°C).
2. Start the engine.
3. Raise and safely support the vehicle.
4. Place a drain pan under the transmission.
5. Allow the ATF temperature to reach 95° - 113°F (35° - 45°C). Automatic transmission fluid inspection plug
   
   
6. Remove the inspection plug from the transmission housing. Fluid is pipe will run out. If fluid continues to drip out, no additional fluid is needed. If only the fluid in the overflow pipe runs out, additional fluid is needed.

To Fill:
Automatic transmission fluid filler pipe

1. Pry the cap from the filler pipe. The cap locking device will be destroyed during removal.
2. Pull the plug from the filler pipe.
3. Add fluid slowly with VAG 1924 or equivalent until fluid runs out of the inspection hole. Install the inspection hole plug.
4. Install the plug in the filler pipe and secure with a new cap.

remove dog house locate test port and install guage should be 45-60 psi

It sounds like an emission problem egr or catalytic convertor

Change the fuel filter, and put a can of Seafoam (from the parts store) into the gas tank, and fill up on top of it with high octane fuel. That should fix the issue.

For all those out there that have had problems with your Chevy Aveo Stalling, inconsistent idling, hard to start, or throttle problems, Hollywood Harv has the answer for you. Try a new Valve Idling Air Cont GM part number 93744675. You only need one and it has to be install by Chevrolet so they can place in the codes to make it work properly. Toss the old one away as most likely has so much carbon build up on the part that it stuck or struggling to function properly. It worked on mine after many different attempts at other stuff! This is a sure winner! Good luck and drive safe! Hollywood Harv

i had this problem with my cherokee your not getting the right fuel mixure