HELP 98 Golf Problems

[cpvwman]

1998 Golf GL 2.0
NO POWER 2000-3000 RPM, OBD II CODES: P0300,P0302,P0304,
FUEL PRESSURES OK, 3 BAR /44PSI @ IDLE VACUUM OFF @ PRESS REG,
2.5 BAR / 36 PSI VACUUM ON @ PRESS REG,
ENGINE OFF, 5 MINUTE RESIDUAL PRESS + 2BAR /35 PSI,

NEW IGN COIL, IGN CABLES, SPARK PLUGS, DISTR. CAP + ROTOR,

IT RUN OK PRIOR TO GETTING A NEW EXHAUST SYSTEM WELDED ON,

EVEN TRIED A NEW AIR MASS METER, ALL TO NO AVAIL,

STRANGE OBSERVATION; WITH THE 3 PRONG PLUG DISCONNECTED @ DISTRIBUTOR,
ENGINE WILL START AND IDLE.

WHAT ELSE NEED I CHECK OUT, I DO NOT HAVE A DECENT WIRING DIAGRAM,
(ALL WE HAVE IS A USELESS HAYNES MANUAL).

PLEASE HELP!

[fil1973]

hi mate, as all of your diag trouble codes seem to be missfire probs,
(since welding your exhaust) is your new exhaust (restricting the system?)

try running the car with the exhaust disconnected,

or has the exhaust been "mig welded" (without) removing the battery lead first, (possibly damaging the cars ecu??)

check voltages etc at your ecu with multimeter using autodata etc,

[halfofnothing]

how does it run when it's up to temp at wide open throttle?