85 MR2 wont rev, engine rattles

Get ECU error codes read at your favorite auto parts store (ask nicely). That should give you a starting point. This is the first thing a dealer would do.

Correct oil used. Level ok? Correct filter? Any lights on dash?

it sounds like the injectors are starting to plug or you may need to use higher octane fuel

Sounds much like a slipped timing belt or one with a tooth or two missing. Since your engine is not an interference type, damage isn't awaiting you as with many other cars but if the belt has more than 60000 miles on it, it's time to change it.
Timing belt installation on many cars is pretty complicated as far as access is concerned so you might want to get a quote from a dealer. If you want to DIY, check MR2 forums and you'll probably find help there.

check the air intake tube to the engine for a crack between the MAF sensor and intake of the engine, pull it off and bend it around. look at the bottom carefully.

the noise is the heat sheild area that is rattling around i have the same problem. I was told it was 'pinking' whihc is when the fuel is not quiet right ( as toyota s are designed to run on 95 octane ) but i had metal parts that where loose around the heat sheild and i had them welded back on. Get them mechanics to have a look - it cost me about £60

system to lean means that there is not enough gas getting into the system try checking fuel filter and fuel injectors that should help you there hope everything works out

Hot weather equals thinner oil equals rattles


If the engine is a high miler try using a multigrade with a higher viscosity or dump a can of STP or Wynns into the engine to bulk out the oil when it is hot

i would have the gas filter replace.have them put
the code reader on the car and check for poss.code

Pound on the catalytic converter, you will probably find your rattle inside, if so, you will need a new one, also check for any loose clamps or rings that have come loose, just pound on your exhaust with the side of your fist, you should find your rattle, or sometimes the heat sheilds above the exhaust come loose.