1.8T MAF / Vacuum leak Mystery

I'm running a 1.8t in my Mk1 which seems to run great with the MAF sensor disconnected although very fuel rich.
Connect the MAF and the car runs like a dog when accelerating under load between 2000/4000 revs. But idle fine.
I've tried a second hand and new MAF sensor which has no effect.

Any one got an idea what the problem is he? I going to look for a vacuum leak next but most things I've read say the car
would struggle to idle if it was a vacuum leak and the pipe work is visual in good condition?

There are lots of pipe and connections. Are there any problem area and what is the best way to trace the air leak?

Any help appreciated.

Yes, the Tube that connects the MAF to the Throttlebody  is known to get cracked along the flex tube.

It is also known to get weak spots at the connections on the Air tube where the PVC connects to it as well as the ISV.  I have a how do I fix that in the DIY link.

There is the Idle Bypass valve on the back of the throttlebody 7mm Brass screw if it turns my hand it is leaking count the turns to remove write that down.  Got to the Hardware store and get a new o-ring.

There is the Hard line from the Brake Booster to the Throttlebody, as well as you could have a bad check valve.

Get it hot and spray the connectors with Ether.

Do your defroster/a/c vents work ok?

Try unplugging the CTS and see if it goes away,  if it don't then reconnect it and disconnect the o2 sensor if installed and again worse or better.

Thanks for quick reply. Briano

Hoping to get some time at the weekend to have a look. you have given me a great starting point. 

Cheers

So had a chance to have a look at the vacuum system this week end.

The engine is a AUQ so don't seem to have Idle bypass valve on throttle body. The pipes all look ok but a lot of the smaller once need better clips.
The N249 solenoid valve look to be disconnected and n75 look visually ok. Brake booster to throttle body may be a problem area because the brake connector may suspect. The discharge pipe & the pancake pipe also may be a problem area, but I thing I need to pressure / smoke test the system to see any leak.

I have another problem to sort first. The OBD Port has gone dead - no power. All part of the fun of running a modified retro classic.
 

I have seen the idle by-pass screw on the back side of the TB and it is smaller than the ones I have and may have a lead seal over it.  I have seen folks that needed a
7mm deep well to get to it.