90 8v GTI Losing Performance"HELP"

[True Blue GTI]

I've got a 90 8v GTI That will run OK for days and then all of a sudden goes really flat(Loses performance)
an injection specialist took a look but couldn't really help appart from getting it running better when it's Behaving.

[golfvr6]

Any other symptoms?

[True Blue GTI]

When runnung in slow traffic the engine sometimes surges a little.(The tick over is a little random too).
The guy who tuned and checked it said he had to adjust the timing but i was told the timing is controlled by the ecu.

[golfvr6]

Look at the usual suspects ie. air flow meter and oyxgen sensor(if fitted). You are correct about the ignition timing, it is a controlled by the ecu , so is non-adjustable.

[mk1]

Check the pleated rubber hose from the air flow meter to the throttle body for splits. Base timing is adjustable on this system, 6 degrees i think

[golfvr6]

I think mixture and idle was also adjustable on the early digifant.

[Slim Shady]

try drilling the airbox
 

[golfvr6]

Yeah mate, talk sense when you know some  

[Tornado-red_gti]

 Could it be the knock sensor?

[golfvr6]

Could be, likely to either a vacuum leak or a faulty sensor.