1.8 Mp9 idle and throttle issue

[MNRNEL]

Gents I really need help.

Recently did a 1.8 mp9 conversion on a mk1
ECU and harness that goes with it.

Basically what's happening is it idles at like 3000rpm then drops and comes back to 3000rpm.,jerking back and fourth continuesly like it completely cuts out and starts again quickly . If I let off the throttle the rpm jumps before coming down.

When driving open throttle everything seems fine but underpowered.

Things I've tried:
Does the same thing If I disconnect the throttle cable
Checked pin outs on the harness, 100%
Tested the ecu on another car, 100%
Replaced the 4pin temp sensor
Replaced the Map sensor
Replaced the coil
Replaced the fuel pump
Replaced the fuel pressure regulator
Replaced the fuel rail
Cleaned the throttle body
Can't find any vacuum leaks.

I'm willing to try anything, please throw me with suggestions

[Jetta2]

Is the ECU the correct one for the 1.8, or from something like a 1.4 or 1.6?

[MNRNEL]

Ecu that comes with the motor, oem... Tested on another 1.8. Ran perfect

[Rudi46]

How sure are you the wiring is fine, can be 2 wires that's damaged and touching of a sensor. Plug out ECU and all sensors Exct.
Test the if there is continuity between any of the wire and also maybe test if one of the wire isn't completely off. By checking continuity between the 2 points of the wires. ECU side and Map sensor side.

Had a issue with this once on a car where the map sensor wire was damaged.

Did you scan ECU for errors?