difficult to explain.....

But here goes.....
1.8 FL1 'W' plate 2000.
Engine in perfect condition, no rattles, no coolant loss, no oil loss etc etc.
Now, at cruising speed on motorway or similar, lets say 70mph, just touching the throttle to maintain speed, the motor is quiet, and very smooth. Approach an incline, or try and overtake something, and it becomes quite 'lumpy' when I bury the throttle to the floor. Almost like a mis-fire, but not, -if you understand!! The motor seems reluctant to pull properly.
Any ideas?
The spark plugs were renewed 20,000 miles ago, so maybe they are ready to be replaced?
Thanks,
Russ

sounds like a plug fault mine was doing the same thing cruising along OK then missing when you boot it.
I changed No 1 plug and it was fine
OH and check that all the plugs are tight it may be just me but even though I used a torque wrench to fit them when I changed the plug it was only finger tight
Come to think of it maybe it was the loose plug that was causing the problem.