E30 L-Jet M20 idle low & rich

[Wingzero]

Hi everyone.

So my E30 320i (L-Jet M20B20) has had a new head gasket (thicker one), new head bolts, new spark plugs, and all the gaskets that come with a gasket kit.
After putting everything in order, we did the fine tuning in this order

1) Engine start, then Ignition timing
2) Valve clearances
3) First drive.

After starting it up, it goes through cold start just fine. Once it warms up, the diaphragm doesn't push the throttle bracket to idle at around 800rpm. It just stays low and stalls out. I don't want to adjust it too much because the screw is on the verge of falling out if I draw it out any further. Once I remove the vac pipe from the diaphragm, then the engine revs high as it's supposed to.

On top of that, it idles really rich. Not black smoke but enough to feel dizzy about it.

I'm ordering a new distributor cap as it's been on and off a few times. I have a feeling that a cable from the ignition control module looks a bit mangled but isn't frayed. Just squashed. Does it need changing?

My next step is to go to the MOT emissions test centre and let them do their magic since I feel like I'm a bit out of my depth.

Is there a way to test for vacuum leaks better than going to each pipe one by one and rubbing brake cleaner on it?

Any other suggestions would be appreciated.

Thanks