1986 toyota cressida starts and idols fine but when you start to drive it it acts like its starving for fuel have replaced mass air flow,o2 sensor(as this is what the computer said was wrong-replaced now no service light comes on) also new computer,plugs,wires,rotor and cap,and had injectors cleaned.Still same issue spit and sputters once in awhile exhaust pops like a slight backfire...but sometimes it runs fine.

The poor performance of the car makes these faults to come up and undermine the working of the engine. In this case it seems that the fault seems related with an electric circuit, possible there is no trigger from the ignition unit or there is fauty timing settings.

So to start off we need to check from the fuel tank. Splutering happens even if the fuel contains impurities and specially water. If so this can come up with the pumping when the tank gets empty and produce misfiring, splutter and jerks. So a check on the fuel filter will confirm this as it will be seen, if so remove and clean tank and change the filter. We then come to the fuel pump as the fuel mixing and pressure is determined in this section. You need to have the pump calibrated if the pressure at the injector is low.

Then we must check with the electrics.Since you have changed a whole sett of spares it is important to check the spark intensity .Remove all plugs to check gap and condition of plugs. The black plug indication will confirm that the performance is bad whereas a fully fired plug without deposits must be the ideal view. Check the HT coil and the HT wires, if the intensity is bad this must be swapped and checked to confirm. DO NOT CHANGE any part without a confirmation by trying with a replacement from another vehicle or friend. Finally the LT trigger to the coils must be checked be it from the platinum points or an electronic ignition unit. The voltage of the trigger must be high to give the best HT output.

Now use a strobe to check the Timing on the engine. Adjust if needed to see the TOP DEAD CENTER-TDC- mark. If there is valve noise make sure that the tappets are set properly so that the valves seat firmly for the best compression. Also check compression of engine if there is imbalance on the engine or reduced power.

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Have you had the cat converter checked to see if it is plugged. The symptoms your describing about not having any power and reading what you have done to correct the issue leads me to lean towords a plugged converter or possibly the engine valves. Whats the milage on the engine and has it ever had any valve work done, and has the cat converter ever been changed?

Most common causes of internal catalyst failure is due to unburned fuel, lead, phosphorous or engine coolant contamination. These contaminants can begin to clog the catalytic converter and restrict exhaust flow through the system. When this occurs, the back pressure of the exhaust builds up between the exhaust manifold and the converter. Because the exhaust system is not allowed to breathe well, engine stalls, decreased fuel efficiency, lack of acceleration and overall engine performance are compromised.

Back pressure can be tested from the tailpipe of the exhaust system by determining if enough exhaust flow is passing through it. If you plug the tailpipe with a safety glove on your hand and a thick protective rag and then the engine dies, you have restricted exhaust flow. Since many components comprise the entire exhaust system, this test does not necessarily condemn the converter. An exhaust pressure tester could be used to determine catalyst failure. Drilling a small hole in the pipe in front of the converter and inserting the tester tube to determine if pressure is present would be the next step. If pressure is present in the pipe, then the exhaust flow is not passing through the converter as it should be.

The oxygen sensor is one of the more common causes of catalyst failure. This happens over a period of time, but the sensor's responsibility to monitor the air-to-fuel ratio expelled from the combustible engine. When it fails, the computer to the vehicle fails to register the information and make the necessary adjustments to the ratio. This can cause either a rich or lean fuel mixture, which will eventually cause internal catalyst failure. Too much fuel will create too much heat inside the converter and cause the precious metals to melt. This will lead to internal breakdown of the converter and most likely cause clogging of the exhaust flow. Too much air will allow undesirable contaminants and pollutants to slowly clog the passage way of the converter as the particles affix themselves to the precious metals.
Spark plug misfires, failed oxygen sensors, leaded gasoline and oil or coolant contaminants are all contributing factors in breaking down the internal catalyst.