206 gti idle and running problem

[pointz]

I have recently replaced the engine in my 206 gti 138 ew10j4 72k engine that was running well in previous car.

Problem is i forgot to connect crank sensor originally and car wouldn't start.
Plugged crank sensor in and fired straight up and was really really smooth then........

The new problem. After 5 mins of running it starts to run lumpy and progressively gets worse to the point 10 mins ish later it will stall.

If i hold the revs at say 2k revs, the revs slowly drop off and if i try to further rev it it will try to die.

What i have done-

-changed map sensor
-cleaned throttle body and idle control valve and other sensors on tb
-changed temp sensor 
-cleaned egr valve
-fitted brand new crank position sensor.
-put my fault code reader on and got po170 fuel trim malfunction, cleared codes and it hasn't returned even though issue still remains!
-tried ecu reset following the procedure of disconnecting battery etc.

Really want to sort this issue as it runs so sweet on start up.

[pointz]

I haven't checked fuel pressure but i have thought about checking it as a possibility.
I only got a basic obd2 scanner and it doesn't do live scan however it says monitoring is ok.

I have been doing research and believe it could be an injector fault so i ordered a replacement to try.

[pointz]

So i am still having this problem but the idle only starts hunting after i take the car around the block other than that its fine.
What could my problem be?

Im not getting any faults or eml coming on so i don't think its electrical.