Ok, we talk about Toyota then, if the injection is from the year 89, it is possible that it was not subject to the Euro 3 anticontamination regulations (from which the Lambda probes and catalysts began to be mounted).
The truth is that of the Toyota injection system I am not very much, I understand much more of the Bosch, L Jetronic, LH, Motronic, Monojetronic ... and the like systems.
And I can tell you that in all the systems that do not wear Lambda probe there is a CO rule screw and another of RPM in idius with which the mixture is compensated.
Normally the co screw is usually in the air mass meter, next to the air filter, covered with a plastic cap that serves as a seal.
The RPM adjustment screw on idle is in the motor butterfly body and works exactly the same as in a carburetor.
The issue is that if you have assured that the admission collector is stagnant (not between any air without passing through the mass meter), the CO will have to be adjusted to see if the fault is corrected.
To see if there are air leaks, what I do is plug the exhaust tube with an American cloth and tape, then I do the same on the admission side, and I put a small tube through which it puts air at pressure never more than 0.5 bar. Spray soapy water and where bubbles are formed is where air is entering "without permission".
In any case, this injection system has to have a diagnostic code through which and by flickers of the fault light can be seen if there is any sensor or actuator in poor condition (flowmeter, butterfly contactor, motor temperature probes ...)
a greeting.
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