4Runner performance

Maybe a bit under powered, it should at least get to 130ks to 140ks, albeit slowly.

You may need to replace the airfilter, fuel filter, and just a general service, take it to a diesel service centre.

they aren't the most powerfull motor around (read wouldn't pull the skin off a rice pudding) but reliable and strong.

Baz.

Hmmm I had an 84 2.4 Lux, never got anywhere near 140 in standard form.

Picked up a turbo at wreckers and would then cruise all day up and down most hills between Brissy and Rocky at 110-120 but wasn't geared for top end speed.

Those donks are a sound eng BUT very underpowered . However you should be able to do 110/120kph (will get there slowly though) As previously stated get a full service done . Have injectors checked & cleaned or replaced as necessary & fuel distribution pump checked for timing & correct operation.
If you have no intentions of putting a turbo on this eng fit a set of extractors & a 2" free flowing system you will get a increase in performance (not huge but noticeable) you may want to think about a diesel gas conversion you get definite power increase & better fuel consumption . I dont advise a finer filter type air cleaner (i have seen engines dusted with these)
The 2.4 eng is usually reliable & durable just lacking on a few ponies just don't over heat the little donk & don't ask more of it than it can give . concentrate your money on making your engine work its best in standard form then add extractors ,induction improvements & the like after.
Of course you can easily fit a v6 commode (oops i ment commadore) eng to these just watch you driveline though if you do.....666toy

Also check for a stuffed muffler. If the baffles collapse inside they can severely restrict exhaust gas flow.

Are you sure it's the 2.4L diesel as the (October) '89 model 4Runner came out with the 2.8L diesel. The only 2.4L engine was petrol.

It's not a rebadged imported Surf to look like th 4Runner? The Surf's around that year did have the 2.4L diesel but with a factory turbo - wasn't removed was it and sold without?

Diff gearing not changed or wrong sized tyres to give the slow speed? Blocked air filter, blocked exhaust system, poor fuel delivery/timing will give poor top end speed too.

Ex neighbour has an '88 with the 2L (2.4 diesel).