Learn about and examine the block learn multiplier numbers. They can give you hints about what kind of problems you have. A lean mixture might mean you have extra air entering the system through the vacuum system, the EGR or some other gasket. A rich mixture might mean too much fuel caused by a defective fuel canister or excessive fuel pressure.
One cause of stalling with automatic transmission cars is the torque converter lockup solenoid; if it doesn't disengage on deceleration, the engine will usually stall. I have a manual transmission so I don't have direct experience with this but I know the service manual documents how to test for this problem.
One thing I didn't do because I didn't have access to the test equipment was put the car on an engine o-scope. This might have identified the ignition problems caused by my loose spark plugs.
As with debugging computer programs, don't stop when you find the first bug; keep going until you find all the bugs.
After you have fixed a problem (vacuum leak, bad sensor, etc.) run the idle learn procedure. I prefer to do this on when the block is stone cold.
I would personally not attempt any diagnoses without a factory service manual. Having a scan tool is very important. Having a vacuum tester is invaluable (I found two problems within the first 10 minutes of use).
The problems I solved in 1996 had a positive impact on my 1997 smog check. The following table contains the smog check history for my Beretta:
Notice that although the HC numbers went down in 1997, they were still higher than their 1993 values. I suspect this was due to the second defective fuel purge canister solenoid I replaced a few months after my 1997 smog check; you would expect the idle RPM HC count to be high with a bad canister solenoid. The low temperature thermostat that goes with my Hypertech chip may also have some impact; lowering the temperature in the combustion chamber should cause more than the normal amount of fuel to condense on the cylinder walls. There's no oxygen in liquid fuel so it doesn't burn very well; this should show up as HC in the exhaust.
(Numbers in parentheses are allowable, ø means not measured)
2500 RPM Idle RPM HC ppm CO % CO2 % O2 % HC ppm CO % CO2 % O2 % 2001 54 (140) 0.50 (1.00) 14.0 0.4 42 (120) 0.02 (1.00) 14.6 0.0 1999 14 (140) 0.01 (1.00) 14.9 0.1 52 (120) 0.02 (1.00) 14.7 0.1 1997 11 (140) 0.01 (1.00) 14.5 0.4 49 (120) 0.01 (1.00) 14.6 0.3 1995 23 (220) 0.00 (1.20) 15.3 0.3 63 (100) 0.01 (1.00) 15.3 0.3 1993 2 (220) 0.00 (1.20) 15.0 0.4 8 (100) 0.00 (1.00) 15.0 0.3 1991 4 (220) 0.00 (1.20) ø ø 5 (100) 0.00 (1.00) ø ø
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