No revs/power, warning lights, running rough

[I3ATDAN]

VW Polo 1.4 Petrol 2001 Y reg MK 3 Facelift.
So last week the temp gauge started rising quick about a quarter mile from home. Kept going taking it easy and got it back on the drive. Once I had stopped could see coolant steaming off etc.

Refilled the coolant thinking it may have been low to begin with – no luck. Realised the fan wasn’t kicking in. Shorted it out at the rad switch and it ran fine, so replaced the switch – still no luck.

Noticed the rad was cold when heating up. Thermostat was knackered and noticed the base of it had started to melt to the housing. Eased off the melted part and replaced. When refilling the coolant noticed leaking from a crack in stat housing from where I had removed the melted plastic. Replaced the housing, seals etc. No problems. Filled her up again, no leaks all good.

After plugging everything back in and reconnecting the battery it wouldn’t start without my boot all the way down on the accelerator pedal. When it did start it was running real rough, the engine looked like it was going to jump out the bonnet and I had an EPC and check engine light on the dash. Hitting the accelerator gave me no revs at all but it would sit there coughing and spluttering whist turning over for a few minutes before cutting out. Repeating this process and the engine began to run smoother and smoother without cutting out - but nowhere near perfect. Occasionally when I turned it over with my foot down it would rev all the way up, but as soon as I took my foot off and tried again the revs were gone/limited to 1500 rpm.

Eventually when it revved up on start I lost my rag and just kept my foot down revving the balls off of it for a few seconds. At this point the EPC and check engine light disappeared and it sat there ticking over fine with revs. Left it running for a while, no overheating, fan kicks in just fine.

I took it for a gentle spin round the block and it drove fine. However with no warning it will cut out, lights back on, revs limited.

From what I’m reading everyone’s saying it needs to go in the shop to get the EPC code. Personally there’s a line for how much hassle and money I’m willing to spend on this before I scrap it and buy me a new set of wheels. Does anyone know what lead/software (link if possible) I would need to plug in with a laptop myself?

Of course if anyone can tip me off as to what this might be or what to check next that would be greatly appreciated.

A few things to note.

Car was running fine before the thermostat housing swap.

When swapping out the stat housing it began to rain for a short while. Not thinking anything of it I pushed through. Could water under the hood cause any issues?

Thanks in advance all.