That strong fuel smell could easily be clutch lining burning, try starting off in third gear, the engine should stall straight out, if it doesn't and the engine revs continue high with the car gradually moving away then almost certainly the clutch is toast.

Don't leave it, if it hasn't already the flywheel itself can be ruined by a severaly worn clutch which will put the cost up considerably.

Can't comment on the fuel filter, but it could probably do with a service and checkover at a good indy workshop anyway, maybe someone different to the chap you've already had out.

I like the Matiz, super little town car.

Edited by gordonbennet on 20/02/2023 at 15:46

My guess is you have a blocked exhaust. Some simple checks by someone who knows what they're doing will confirm this or otherwise.

Sounds reasonable, or air filter possibly

A very long shot but worth checking and/or having a mechanic inspect - when was the cambelt last changed or inspected?. I can find reviews saying that it's vital that it's done on schedule but sadly not why.

The need to replace a cambelt in itself will not affect engine performance or restore lost performance. However if the valve timing is incorrect for whatever reason then it would. If the valve timing has moved then something is wrong. Most likely the crankshaft or camshaft keys worn or the belt tension is slack. That should be pretty obvious to anyone though.

No harm in looking (with appropriate care to avoid introducing dirt into the engine) but cars are very very insensitive to restricted air filters.

A feedback-loop controlled car (which this almost certainly is) is very, very, very insensitive to a restricted air filter.

In extremis it''d loose power, but it shouldn't run rich because the engine management should prevent it.

This implies that this cause shouldn't result in the "fuel smell" symptom.

A clogged fuel filter could also restrict power, but it shouldn't result in a "fuel smell" unless back pressure from the blockage is causing an actual fuel leak.

If this was the case, it'd likely be constant rather than just on the uphill.

While these would both be cheap fixes, my money is on clutch slip, which unfortunately isn't, but you can test for it, as described above, before committing to the spend.

Something to check/jhave checked before replacement might be clutch adjustment.

While I believe most cars have hydraulic clutch control, which doesn't normally require adjustment, a couple of my smaller, cheaper cars (Renault 5, Daihatsu Skywing) at least have had cable actuated clutches which needed adjusted ocaisionally.

A blocked exhaust would also seem to be a possibility. On a non-cat car (which yours almost certainly isn't) this is often easy to fix, but also much less likely,

A cat equipped car would probably require a new catalytic converter.

Easiest (as in most easily interpreted) way to diagnose that is to remove your oxygen sensor, which "opens up" the exhaust, bypassing the exhaust restriction and restoring power.

Its supposed to be diagnosable with a vaccuum gauge too with experience. l couldn't make sense of the results when I tried it.

Edited by edlithgow on 22/02/2023 at 08:41

In addition to the "classic" causes already discussed (which, with the partial exception of a blocked exhaust, which is only likely with a cat-equipped car, and cambelt)

I had a blocked exhaust on a Kia Pride (almost in your territory Ed) that was caused by corrosion in the back box, allowing the wadding to block the silencer outlet. Spent an hour with a wire clothes hanger, bent into a hook on the end, fishing it all out.

Mon 20 Feb 2023 14:56 Useless female Your question was: My matiz has been fine for the few months I’ve had it. 14 years old but only 45k on the clock. Normally it would zip up a big hill at 60/70mph but over the last couple of weeks it’s been struggling to get uphill. Last time I drove it it struggled to make 20mph on the hills and was slow on the flat and there was an awful strong ‘fuel’ smell when I tried to push it. My experience has been: I had strong fuel smell in my Matiz and lack of power. Believe it or not, it turns out that one of the spark plugs had become unscrewed enough to allow fuel to leak out and could be smelt in the car and power was affected as well. Turns out that spark plugs have to be tightened with a very narrow headed wrench to allow it to tighten the plug. Also, the high tension leads had decayed to a point where it was making it run rough and also added to the lack of power.

A loose spark plug would sound like a chuffing steam train, as well as an engine misfire which the OP has not mentioned. The engine would also misfire if a plug lead had gone down, more so under load. It won't be any of these if the engine runs smoothly albeit very under powered.