Toyota Repair: 91 Toyota pick up emission problem, fuel pressure regulator, air filter oil

Question
I own a 91 pick up with a 2.4L engine.  It has failed the emission test twice.  After the 1st fail I changed the air filter, oil (it smelled like there was fuel in it), found an exhaust leak so I changed the muffler and tailpipe, changed the plugs and rotor.  It was better but failed the second time.  The HC was 187ppm and the CO percent was 6.57 both at 40 km/h. Both readings were high at curb idle as well.  The check engine lite has not been on so I am not sure whether to change the O2 sensor.  Saying that the idiot lites come on before start up but the dash lites do not work to see the dash at night(a question for another time).  I don't think its related but I thought I better give you the whole story. The truck is new to me but the previous owner gave me all of the maintenance history and there is nothing I can see other than regular maintenance.  Oh Yeah it has 140,000 kilometers on it.  It seems to run fine although I do notice that the gas mileage is not that great.  Any advice would be great

Answer
The HC reading not all that bad, I think 100ppm is the limit, the cause for concern is the high CO reading it indicates the engine is running rich(about six times the limit) I also think that when the CO problem is fixed the HC will come down.
Basically the engine is getting too much fuel and not enough air, have the O2 sensor tested to see if it working correctly, it can be the source of the problem especially if there is an exhaust leak in front of it,it can also be caused by a failing fuel pressure regulator,or a sticking open of the cold start injector or even one of the fuel injectors.