Vauxhall Astra 1.8 16V SXi 3door Hatchback 2001

Hello.

I have the Vauxhall Astra 1.8 16V SXi 3door Hatchback 2001.

Recently I have noticed the car seems to be holding back quite a bit. When I try putting my foot to the floor, at about 40-70mph the car holds back and doesn’t accelerate as it should, then all of a sudden it kinda starts to pick up. It feels like sticking points. It doesn’t seem as quick as it was when I 1st got it either.

I have done a few things to try to troubleshoot the problem with no avail. Here’s what I’ve done:

Oil change.
Replaced oil filter.
Replaced air filter.
Changed spark plugs.
Replaced coolant.
Cleaned butterfly valve with throttle cleaner.
Replaced fuel filter.
Added valve cleaner to fuel.
Added petrol cleaner to fuel.

Yet all this has made no difference whatsoever to the problem. Besides a general service, my mechanical knowledge is sketchy to say the least, so I’m a little stumped.

Can anyone possibly offer me any assistance to what the problem may be?

Many thanks.

Llew.