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					Originally Posted by grokicki
					
				 My mechanic, who is a pro and very good, has spend hours on this car and insists it's not a vac leak.  Is he correct that the oxygen sensor needs to have 12 volts to the heater unit on it full time? | 
	
   Not above 5K RPM [ WOT]
 Have him do an 02 sensor test .
 You can also check to see if the O2 is reading lean condition when the sig wire is to the ECU is disconnected.. if it does , then a vac leak is suspect.
 Both the EGR and Purge valve can be leaking on a 104 HFM system and you will not hear/see it b/c the leak is internal to the vac system........... my first suspect after 02 test verification on a 104 would be purge valve