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.

[Mr2Mike]

Have you checked fuel rail pressure? Does ODB2 live data show reasonable values for coolant temperature, MAP etc. when the problem occurs?

[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.

[Sensibleboy]

At what temperature does lambda control kick in on standard engines? I'm only familiar with aftermarket ECUs and mine cuts in at 70 degrees. Before that it doesn't use the lambda sensor to run the engine.
Other than that these EW engines traditionally had a problem with dodgy hydraulic lifters. They normally run rough from cold though and improve as things warm up slightly. Although some engines will behave differently.