The Toyota SR5 (22RE Engine) required 5 degrees BTDC (before top dead center) ignition timing. Setting the ignition timing correctly will absolutely lower HC emissions. By allowing the ignition to fire sooner than its current setting (12 btdc) you will be giving the engine more time to burn the air/fuel mixture; lowering HC and CO. The only thing that might happen in this case however is that if your engine has any cooling problems or defective EGR valve system, NO emissions will increase. Non the less however, ignition timing has to be set to manufacture specifications or else your Toyota SR5 has no chance of passing the smog check.
The begin setting the ignition timing you must first located the timing diagnostics connector (T-E1). Short circuit the terminals (pins E1 and Te1). A paperclip is commonly used. Your engine's idle will drop when you short the connector. This is normal. Just remember to un-short the connector after the timing is corrected.
Next, connect your timing gun to the number 1 cylinder spark plug wire. Start and idle the engine. Loosen the distributor adjustment bolt just enough that the distributor can be turned by hand. Using your timing gun set the ignition timing to 5 degrees (BTDC). This is done by aiming your timing gun (strobe light) toward the marks on the engine's crankshaft pulley. Turn the (clockwise) until the timing mark is at 5 degrees. Once you are certain the marking is correct go ahead and tighten the distributor adjustment bolt back.
Finally, disconnect the timing diagnostics connected.
