MK3 7MGE Emissions Problem

[Hoodlum1982]

Hi, wondering if anyone could help me here.. I`ve got a 1990 7MGE supra and has just failed it`s mot on emissions as the CO is too high, was coming up on the machine at 4.10% and it has to be under 3.50%. So far i have changed the plugs, put a bit of injector cleaner through it (only had it running outside the house for 20 mins and a short drive to mot station though), and i have ordered a coolant temp sensor.
Tried diagnostics on it but had no fault codes, does anyone have any more ideas? Do these have a mixture screw anywhere?
The mot tester said usually there is a screw around the throttle body and if we can find it then we can adjust it while it`s on the machine but i can`t seem to find anything.
Any help would be much appreciated as i am stumped here.
Cheers