ok so i changed the o2 sensor..... gas mileage went up for about a tank and a 1/2 then DROPPED major... im down to 13.5 mpg .... any suggestions?

What brand sensor did you use?

AcDelco.... i dont know if this is important or not but a rubber elbow just kinda fell down....when i changed the o2, never did figure out what it was attached to, engine runs fine no vacuum leaks or anythin......didnt POP off, no exposed hoses or anythin that i saw..

*bump*

I bet it was attached to a black reservior just to the left of the brake booster. It should have two posts with two vacuum lines attached.

That rubber elbow might have come off the bottom of the blower motor, I think it directs some air to the motor windings.

no it came from lower down on the engine, and all vacuum is still good im wondering if it was somethin dropped down there when they changed out my vacuum booster and master cyl.

i have a similar prob on my 87 but i think its due to a slow responding temp sensor. does your bonne idle high?
if so then maybe you need a new temp sensor (i think your temp guage can still be good) a scantool would help in this dept but i dont have one. anyways good luck
mike D

fuddy or will, any ideas on what this mystery piece might be?

Get us a picture of it.