About half of the ECU codes stored on the first & second generation EFI Toyotas don't show a constant blinking check engine light therefore you must pull the ECU codes to see if a fault is registered.
To pull the ECU codes:
All 1980-1995 and including 1995 EFI equipped vehicle allow you to find engine and related faults by pulling the ECU (computer) codes without the need for a handheld OBDII diagnosis scanner, the sites listed below have the fault codes needed to pull the codes and the instructions on how to do it:
(auto tranny codes)
Pulling the ECU (EFI computer) codes is the first thing I do to diagnosis a problem thereafter I reset the ECU to see if the same problems show up and if so I then take voltage measurements at each ECU wire both with the engine running and not and compare with the factory service manual, I also close the ignition switch after a cold engine and also after a warm engine and compare the resistance values with the factory service manual. This technique will completely isolate your problem without having to do trial and error and it is the technique I use when repairing tv's, vcr's, home/car audio.
Lots of city miles combined with low octane fuel & no Techtron fuel additive (cleaner) creates excessive throttle body carbon build up (gunk) so throttle body must be cleaned.
To clean the throttle body remove the air intake hose and examine the intake and throttle body for excessive carbon build up if found then buy a can of throttle body cleaner labeled "safe on oxygen sensors,TPS's and catalytic converters" do not use carb cleaner make sure your engine is fully warmed up prior to using as when the throttle body is hot it dissolves the carbon easily and quickly.
The labels usually specify to park the vehicle at ground level (0 degrees,no inclination) and have the engine running but I disagree I instead park the vehicle on a hill facing down and shut the engine off and hold a rag below the lip of the throttle body and poor the stuff and use a tooth brush. You can also use "Sea Foam" the best engine cleaner:
available in Canada through UAP/NAPA Auto Parts Stores.
The oxygen sensor is replaced for free in the USA only when the vehicle reaches it's first 80 000 miles regardless of the age & number of owners as stated in the factory owner's manual in the maintenance section,some Toyota dealerships are reluctant to replace it for free if that happens contact the Toyota regional head office for your region where they will give your local dealership 48 hours to comply.
On average the oxygen sensors should be replaced every 6 years or 100 000 miles or so which ever comes first as stated in the owner's manual,warranty booklet and factory service manual.
Symptoms of a bad o2 sensor are poor gas mileage,hesistation in acceleration,worse emissions,and in severe cases after the stat opens the engine can no longer maintain stable 750 rpm (with manual 5 spd tranny) idle and the engine begins to stall.
The 02 sensor is designed to function once the vehicle has warmed up which is about after 10 minutes where the thermostat begins to open at 190 or 195 degrees Ferenheit depending on thermostat then the vehicles ECU system enters what they call a "closed loop system" then the exhaust manifold's temperature reaches 400 degree Ferenheit (I think)that's where the sensor starts to do it's job which is usually when the thermostat first opens up then the oxygen sensor senses the ratio of air to fuel and sends a signal back to the ECU then ECU compensates by increasing or decrease the open time for the fuel injectors to pump fuel.
So usually the problem of stalling shows up after about 10 minutes of driving or so.Many folks think that the o2 sensor is bad but an exhaust leak can cause excess oxygen to enter the exhaust system thereby fooling the sensor into thinking there is too much oxygen,there are other problems that could cause it to give false reading such as a vaccuum leak.
If you discover that the o2 sensor is bad and it is not under warranty then from my/others experience/research purchase an o2 sensor in the following order:
1)Toyota (NipponDenso now called Denso)
2)Denso aftermarket (Same as original but sold aftermarket)
3)NTK (oxygen sensor division of NGK)
(10% shipping by Fed Ex or free shipping with $100 & over speak to Roger at 1-888-271-3948)
Repairs TV's,VCR's,home/car audio out of my apartment