Ideas on this one...

My car is too odd. I've had bad gas mileage (by my standards), and have had a few posts on this issue. It's gotten weirder. My car had gone from 27 MPG highway down to 14 MPG, regardless of where or how I drove. Thing was running real rich. I also had an issue with fluctuating readings on my volt gauge, it would dip kind of low for the most part, even though there was a new battery and alt. I messed around with some of the wiring, including by the battery and the starter solenoid. The volt gauge was up more consitently, and my gas mileage bumped up to 17 MPG, a little lower if I stomped now, but the way it should probably run. I brought the car to the shop, had the ECT, the t-stat (went back to stock), and the O2's replaced. We also discovered that a bad ground was causing the volt fluctuations. Now I'm back down to 14 MPG and running rich again. What the heck is up with this thing?

I had an adjustable FPR installed and adjusted not too long ago in response to this issue. It didn't help.

No codes, except for the vapor cannister, but I never had that hooked up.

There's another thread with a similar issue that I jumped into. The car runs excellent. It used to have a real bad surge problem, but has since gone away. Every now and then you hear a bit of a 'wave' sound in the idle, almost like a mini-surge, but nothing that only the owner would notice. The issue started around the time I had my heads put in the car, but may have started before. The decline in mileage was gradual, not an overnight thing. The other post I'm in someone mentioned injectors being stuck open. Possibilty? I think it's the only thing I have not yet replaced.