Big fule consumption and jerks at higher speed/Rpm.

I already have a post but I changed alot of things by now. I have a 96 jetta that eats about 21 mpg on the freeway and is super slow. I found out that one of the spark wires had a hole in it so I just changed all the wires. and Distributer cap and rotter. And I changed the sparks. Also a couple of days ago I changed the oxygen sensor on it to. So I still have the check engine light on and the same code-"p0171 system to lean (bank 1). The thing that I hate about the car is that is is so stinking slow. It feels like not all the cylinders are working properly. Like when I press the gas peddle all the way. The Rpms go up really slolwy and the car makes a noise vhmmmoooooooooooo... the whole time when I accelarate. But when standing in nutral it sounds perfect. The mechanic said it soinds alright to when it was in his place. Also when I go up the hill or go to like 70-80 mph the car jerkes every like 2 seconds and there is like no power. I have no idea what to check any more. I have an after market air filter and so I asked the mechanic if that has anything to do with it. But he said there is for sure enough air going in. Also I noticed yesterday that the cables that hook up to the fuel injectors are tapes with black tape. It looks like some one has been doing something on there before I got the car. But if there is no contact on the fuel injectors then wouldn't the car not work at all. I also noticed that there is oil on my trnsmission on the bottom of the car. I doing know , maybe then it is the transmission slipping. All the gears switch perfectly I have no idea what it is then that a transmission slips. Maybe that is the problem. Also the car some times also has problems starting. That when it does start there is a bunch of blue smoke behind. If anyone knows what the problem is I would really really appreciate it.

It was actually I needed to change all my engine gaskets and belts. The girkings was because some of the gases where leaking out. the car runs like a clock now. If anyone has this problem you know what to do now.

It was actually I needed to change all my engine gaskets and belts. The girkings was because some of the gases where leaking out. the car runs like a clock now. If anyone has this problem you know what to do now.
hi it seems i have same problem also can u tell me more specific like what gaskets and what belts and how much $ it cost u for all of that.i have golf mk3 '94 2.0 automatic.THX