E30 318is - Engine dies when touching a specific wire

[E30REDD]

When the engine is running and I just touch this wire, the engine dies for a second and then wakes up to life again. It doesn't completely shut down, but it's struggeling to keep running for a second.

I noticed that this only happens when the engine is cold. When the engine is warm I can bend the cable and touch it how much I want, without any rpm changes from the engine.

What does the cable do and why is it like this?

[TPS]

Its the TPS I think

[Brianmoooore]

Just looked here from your other thread. While you have the ECU plug off, check the TPS from there. There should be a fixed resistance between pins 44 and 59, which shouldn't vary as you move the throttle or wriggle the wire, and there should be a varying resistance between 12 and both of the other pins as you move the throttle. One should increase as the other decreases, and again, shouldn't be affected by wriggling the wire.
Mark the pins you are interested in on the ECU plug with dabs of ink from coloured permanent markers.