why is my 2001 golf junk? on 2001 Volkswagen Golf

it is a 2.0L engine, my rpms wont go over 3000rpm which is stopping it from shifting properly, wont go any faster then 110kms and sometimes only 70kms.i have back pressure in my gas tank, but whas told that that is a good thing. my epc light was on but i changed the throttle control valve and it whent out. i also did a complete tune up,plugs,oil,air filter etc. i know it is something small and simple but im just not sure where to start.. any ideas? thanks in advance

Asked by for the 2001 Volkswagen Golf
To answer your question, it is not just your VW!!
WASTE of time , but funny..........never mind
i had it scanned and there were 10 different codes saying short to ground. i checked all the grounds in the car changed the whole air intake changed the throttle body. checked that all wires and plugs were tight... dont know where to go from here
Codes indicating 'short TO ground' NOT 'short AT ground'........... A short at a groung TO aground is redundant. LOOK for a power or 'input(signal) wire that is damaged and touching a 'grounding source' in the harness somewhere. The codes indicate which circuit is affected , you will need diagrams of the circuit(s) to properly trace and perform necessary testing. LIVE data will help in pinpointing the sensor(s) affected. APPS1 or APPS2 , ETC TAC etc.
1 more answer , 2 more comments
Are you able to scan 'live data' , to see what the basics such as TPS , spark timing and cam sensor say?
it is none of the above. it is electric throttle valve so it does not have a tps
What senses how far open , or how far into the throttle then? Is it carbed? They might call it something different on it , but the PCM still needs input! SO, back to my question , are you able to scan live data?