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If the distributer will not turn to get the ignition timing in the belt is off one tooth. What kind of timing belt are you using. Do you need the Toyota instructions? Do you have the numbers on the HC failure and CO numbers?
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The instructions are good provided you got everything lined up right. My concern is that the marks are not lining up, you mentioned they were off 1/4 tooth? With the crank pulley at 0 deg. Is the hole lining up with the indicator on the camshaft mark. The code 71 is egr low flow this should not have anything to do with the timing. Same goes for 25 and 26. Even if the timing is off a 1/4 of a tooth It should not set those codes. Are you in California or have California emissions on this car.
If you are certain 100% the timing belt is in time check the vacuum on the engine with a vacuum gauge. You need at least 19 inches.
Are the plugs fouling black?
When the car is running rough pull the brake booster hose does the engine speed up and smooth out?
91 depending on the production date could be fuel injected or carburated especially if it is a california emission car. Is yours fuel injected or carburated? You mention near the carb before I assume you have a carb YES? This can change the direction we need to go in.
There should be a vacuum port where the hose for the map sensor attach's. tee in there or remove the brake hose and use an adapter if you have one big enough. Assuming you have the valve timing correct which it sounds like you do based on your description we are going to need to run some electrical test to find out which sensor is causing the vehicle to run rich. Do you have a volt/ohmmeter and know how to use it?
Was this problem here before you did all of the work?
Check the water temperature sensor for the efi computer. Click on the link below for diagram. The sensor should be green and have an electrical connector. The black wire with red tracer should have .4 to .5 volts when the engine is warmed up. If it stays above .75 to 1.25 volts it will make the car run rich. Ideally check the voltage at the computer pin number 4 connector A.
Check the map sensor also it is the other main player for fuel injection duration.
Will you meter give you a millisecond read out of the injection duration? You might consider renting a scan tool if you are going to continue diagnosing this yourself.
Those numbers are good you can rule out the water temp sensor if it is presently running rich and that is the voltage.
The vacuum numbers are to low. This in turn is causing the map sensor to make the computer make the injection time to long. It sees lower then normal vacuum and things the car is accelerating so it calls for more fuel. Tight valves or cam timing off is the mostly likely problem. Distributer timing can affect it also. The VCC 5 volt is a good number. The center pin or wire should fluctuate in voltage as vacuum increases or decreases. See the chart I sent above.
The vacuum on the engine is critical to make this system and engine perform properly.
The actual spark timing adjustment is the only thing in the distributer that will affect engine performance and vacuum. Make sure you jumper the check connector to set base timing.
Click on the link below.