Well I've had my Golf Tdi 2003 for a while and noticed that after a few months that I was getting around 37 mile per gallon on average. I know I needed to do some minor maintenance check ups . I just recently changed the fuel filter a few days ago and decide to delete the screen in the air intake snorkel, check the egr valve, and check the air filter today. I noticed it was pretty dirty and when I removed the filter I left the vacuum lines attached and simply unplugged the maf sensor. Then I decide to check the pressure release valve in the fuel pump. While loosing the pressure release valve I notice some air in the clear tube connected to the fuel pump. I used a gator grip and noticed after the fact that what I thought was a sticky valve was myself creating score marks on the fuel pump due to tight clearance I'ts not extremely bad but I've read on how sensitive those fuel pumps can be. Well I tightened things up because the valve seemed good and now my car is running rough. I was thinking it could be because of the air in the line and drove it around for 20 minutes. Starts smooth then starts to idle real rough and when driving it seem to want to stay revved. It continued to run rough so oh course I was Im trying to determine what could be the issue if it just needs a simple bleed at the injectors or that its a more serious issue. I like to worry and over-analyze things by always assume the worst. I called it a night after I noticed it finally kicked out a cel code. Im thinking it could be six possible things. One a simple malfunction of the maf so tonight I pulled the maf out when the car was idling and it ran rougher (after the cel), two that it be an air leak at the score marks near the 2nd gasket down from the top of the fuel injector pump for a manual gold tdi ( doubtful marks on the aluminum not close to the seal), 3 simply air in the system, 4 i noticed a draft near the air filter when I reinstalled the old one because have not purchased a new one yet ( tomorrow)- Is the filter rubber seal suppose to be tuck in? , Seems like it 5. -vaccum lines have cracked near air filter or maf sensor 6. dirt got into the fuel injector pump from the pressure release valve, I noticed there was dirt underneath the bolt when I removed it. Tried to be careful as possible. Well first thing im doing in the morning is take it to get the code read of course but any suggestions would be great. Im hoping it just fuel in the line but it starts up Man this makes me scared to mess with Diesel but I got to say I love this car!