Mk4 2.0 Start up issue

[TheYoungMk4]

Mk4 Golf 2.0 120,000km
At least once every few days my car has serious issue with wanting to start.
It cranks but won't start.
Eventually it will start, it'll idle super rough for about 20 seconds and spew out black smoke.
A warning also flashes on the dash "alternator workshop"
After the car struggles to start, it will constantly rev to about 3-3.5k rpm for a few minutes.
It also does this randomly when driving, it's like the throttles stuck, but any sudden throttle movements make the enginne sputter.
And with it not in gear rpm will fluctuate from 2k-3.5k
Only recently had major done and new timing belt, but the problem was still evident prior to this.

[Bora Sport]

I would get it scanned but my guess would be the inlet water temperature sensor.

[dylan8]

As above would be a good start

[Grenzal]

I had a similar issue in my mk4 2.0 sport, once every 10 or so starts it wouldn't turn over for me, would wait 15 mins and it would start. I had a very rough idle for two years previous yo this and had numerous people look into it with and prevail. Over the course of a year and half the not starting aspect grew more common and eventually it wouldn't start for three hours and had to tow it too a mechanic where it spent the next month with the vw specialist stumped with what was wrong with it. They eventually gave up trying to find what was wrong with it and I got sick of not having a car so I got it back off them, drove it around for a couple more weeks, hoping to not end up in the same predicament and traded it in for a mk6. So long story short, no clue what was wrong with mine but I'd be interested into what is wrong with yours cause I still miss my mk4 haha