I am a new member so appologies for anything I miss out but I could do with some help!

I recently bought a mark 3 golf, 1.8 driver, L reg with 125000 on the clock and it ran smoothly for a few weeks...

Then one morning driving, I put my foot down in 3rd and the revs dropped momentarily and then picked back up again, causing a slight jolting, then sat in traffic, crawling along slowly, on a slight incline, when trying to move off, the revs again dropped drastically and the engine tried to stall. After this trying to pull out at a roundabout, a loud metallic noise could be heard, like a metal on metal sound mixed with an explosion, only usually once of twice. This happened a few mornings. Having driven it for a while, I had noticed that the thermo guage never went above 65-70, so proceeded to change this, successfully as now the temp goes to normal 80-90ish on the dial and this went well for one morning.

Driving the same route this morning, but not at the same point, and the engine had warmed up at this point, the same metallic noise and slight loss of power was made when driving along, going from 2nd to 3rd and it happened more than before, probably 4 or 5 times.

On all occasions, I have driven both at lunch and in the afternoon and have had no problems whatsoever, which is annoying as I cant show the problem to anyone knowledgeable, it just seems to be a morning problem, possibly after the car has sat for 8 or more hours...

Any help/ideas would be great as garages are so expensive and I'd much rather fix it myself, it has been suggested that I clean the throttle body, could this be the sole cause of the problem?

Thanks, John