Hi all, new to this forum as I have recently acquired a 1990 MR2GT that has been sitting for about 7 years.
I have an issue with it running very rich, and won't run cleanly once it has any boost. The previous owner has had a few mods done such as side mount intercooler, larger Garrett turbo (will try to identify it) larger air flow meter that I can't identify, and a big exhaust. There may be more mods that I haven't yet discovered.
It will start and run, once boost is applied it misfires and blows black/blue smoke and fouls plugs.
I want to replace the 02 sensor, but this engine has a single wire sensor, but listings suggest that it should be a four wire sensor? The plug on the loom is only a single wire so I am not sure which to buy.
The engine sounds very quiet and healthy, I believe that the slight blue smoke when running rich is fuel washing oil from the cylinder walls, it does not blow any smoke at low revs or idle.
I have checked the throttle body, it was surprisingly very clean, checked the TPS, replaced the cap and rotor with genuine parts, tested plug leads, all the turbo piping hoses are in great condition, filter (K&N) is very clean.
Can someone please point me in the right direction to rectify issue? What should I be looking for?
Any help appreciated, Tony.

Welcome to 3sgte :) congratulations
 
Need to know which ecu the car is running? Stock toyota, piggyback, aftermarket
 
Regardless of ecu, general info for misfire & Running rich:
 
 
Replace spark components; spark plugs (one heat range colder as sounds like mods and higher boost), get genuine spark leads (or similar quality), new distributor cap. ATS Racing sells a complete tune up kit, or many ways to purchase.
Check timing
Engine upper spray cleaner
Check engine fault codes
Get fuel injectors out and flow / atomisation checked, or if not matched ultrasonic cleaned
Check camshafts / valve clearances

Stock ecu, new genuine cap and rotor, leads test very well, new plugs, may send injectors to be serviced/tested, this does seem a lot more dramatic than a simple tune up though.

Stock ECU.

Online diagnostics is very guessing. Get through the basic list of checks / tune up, check any ECU fault codes.

Once you start modifying, aka aftermarket turbo and/or other bolt ons, the more you modify, the more you need an aftermarket ECU to retune the map for the air / fuel flow at that rpm/throttle position etc.

If it was my mr2, take it to a dyno tune / engine specialist in your state. Best to connect with mr2 owners in your state.

Thank you for the replies, I understand online diagnostics is open to so many variables, and due to previous owners unknown mods, even more variables come into play.
I wasn't sure if this was a common issue, or a known problem at the very least.
Do you know if my 02 sensor should be single wire or 4 wire? The single wire sensors available are listed for 3SGE only from what I've found so far.
The original turbo, AFM and intercooler are with the car and I'm reluctant to fit them, the compressor side of the turbo looks a little oily, maybe a seal gone.....
I have tried the original AFM, no luck there either.
Tony.

The O2 sensor comes in one, two, four wires depending on the year of the mr2. You need to match what your ecu has and being an early model should have less wires. The later the year the more wires, however match what your ecu needs / wires.

The O2 sensor has a small percentage of change in the fuel map. I have not heard of it to be enough to change it enough for it to be blowing smoke as I perceive in the description.

Common is the 3sgte stock ecu runs rich at wide open throttle. That is normal and good.

Depending on carbon deposit (engine upper cleaner), depending on calve spring condition and valve/camshaft clearances, depending on fuel amount and atomisation, spark plugs at correct temperature range, spark components working, will contribute to smoke out the exhaust.

Prior comments is recommended steps of service, seeing a dyno tuner / engine specialist, and getting to know club members in your local area (borrow a sensor and see if it makes any difference).

Boost leak will also cause extra richness, ie beyond the stock 12-13:1.
My dyno report showed 10s even dipping in to the 9s, (and only boosting to 9psi) so built a boost leak tester and found a leak.
Yet to see what the readings are now.
If still too rich, will check fuel pressure, and then the adjustment in the AirFlow meter thingy at the air cleaner. 
Pretty sure this is all doable, would like to get up near 13:1.

Mate who ever did this has no idea. Changing the air flow meter. Your ECU is not getting the correct voltage reading from your air flow meter.  All standard Gen 1 & 2 SW20 3sgte will have a narrow band with one wire. Your ecu only uses the O2 Sensor in closed loop that's cruising with no accelerating to achieve 14.7 fuel ratio. When boosting occurs it will go into open loop that a fuel and ignition map, it needs the correct voltage inputs from your sensors. I would suggest remove air flow meter then add a Map Sensor and invest in a ECU example a Links etc. If not, you will need to check all your voltage reading. Then check ECU voltage parameter input range. Example 1 to 2 volts or is it 0.01 to 5volts and match your sensors.

92, are you responding to me or the OP ?

TwoDogs
92, are you responding to me or the OP ?

Op