Maybe it just needs a service, like engine oil and filter, air filter and spark plugs - NGK brand is what I've always used in our VW Group cars, Mann brand air filter and oil filter. Engine oil, I tend to use Mobil 1 ESP 5W-30, but some cheaper oil like from Castrol or even just Quantum is okay.
5th gear was always intended to be a "cruising" gear, so normally not much accelerating happening when in that gear for a 1.4 8V 84PS engine.
Ignition coils on these cars can give problems, but in my experience of having 2 cars with these engines, they either work faultlessly or fail - at which point the faulty one gets replaced - leaving spark plugs in for far too long in time and miles, can end up with the spark plugs failing and that means failing to spark 100% of the time, and that can leave the coil(s) being subjected to "too high" an output voltage spike, which will weaken or force them to fail.
Treat it to a full tank of UL+ ie 97 or 98 or 99 octane petrol and drive it "firmly" while consuming that fuel as that might just "clean it up/out" enough to improve its performance - ideally after servicing it properly.
Finally, does it suffer from "pinking", if so then it is probably burning some engine oil so should get its oil separator cleaned or more usefully, replaced - you'll soon know if it is burning engine oil as the oil level will drop over time.
Edit:- changed "16V" to "8V" - what was I thinking about! Or, wait a minute, maybe they were 16V!
