I was pointed over this way by Jack155Q4, I know it's not in the Fiat section but this seemed more appropriate.

History - I saw this engine (a coupe 16vt) running in a scrapper, I completely rebuilt it (one cylinder had gone oval so had to get oversized pistons/rings), put it in an Alfa 145.
The other work done was lightened & balanced flywheel & internals, 3 angle valves & seats cut.

It fired up first time (woohoo) but has never wanted to idle properly and seems sluggish when the engine is accelerated.

I've gone over every air pipe to make sure there are no leaks, proved it by spraying everything with a bit of carb cleaner to see if the revs go up but they don't. The map pipe is good and the original length.

I've cleaned the ICV valve, cleaned the brass screw. It does't make any difference. I noticed by turning the nut on the ICV in a few more turns the idle has picked up slightly. There is a very slight change when the idle screw is turned, but very slight not enough to adjust it to a decent rpm.

I tried setting the idle speed using a FAQ on the Fiat forum but that didn't change it.

It is running a standard map, standard injectors, cams etc. It has standard plugs (6 series, I think bp6re or somewhere similar).

Here is the interesting thing - if I disconnect the MAP sensor connector, it makes no difference to the running.
If I disconnect the Pierburg connector it also makes no difference.

The wires for both connectors are not broken, they ohm out to the relevant pins on the ecu and the positives switch high.

What happens is when I stamp the throttle the revs increase but not exactly quickly - it doesn't miss fire and the revs do climb, just slowly. It's like it isn't boosting

Can anyone please shed any light on where to start looking at?!!