I'm completely confused here and would appreciate any help. This past weekend I replaced the o2 sensor in my 92 GTA and the mileage has gotten worse than before. At best it hasn't changed at all which was around 16 mpg. While I changed that I also cleaned the IAC valve following instructions I found on this board as well as cleaned some gunk out of the intake with some carb cleaner. Not only is the mpg worse but I can also hear and see the rpms rock slightly back and forth between around 800 and 700 rpms at idle. When I start the car it will go up to 2000 rpms for like two seconds then goes down to normal. Are there two issues related? Any suggestions? Also, the check engine light is not on.

 

Just adding to my original post here. On my way home from work I noticed at least 3 times it felt like the engine missed, very noticable, though it didn't stall. The car has new plugs, wires, distributor and rotor, air filter, fuel filter, pcv valve, as well as the work done mentioned above. Of course, still no codes.

One thing I did notice was it sounds like there is a "whirring" noise coming from the rear of the car. I figured it was the fuel pump since I usually only hear it when I'm near empty, however I have over half a tank and now hear it.

Is my engine just completely boned? I realize this is probably a combination of issues but I'm not sure where to begin here. Last time I checked the fuel pressure it was fine, only thing questionable was when the car was started and put in drive the needle on the gauge jumped up and down, but since I've never checked fuel pressure before I dunno if that's normal or not. That also wouldn't explain the bad mileage. Can anyone help?

 

Think I found the problem. Last night I hooked up a fuel pressure gauge on the fuel rail and turned the key... the pressure went up to about 45 psi then right back down. Looks like it's either the fuel pump or the regulator. The whirring noise is quite loud now. This is gonna get ugly.

 

poor gas mileage, missing @ idle. I bet its your injectors if you still have the originals

 

I haven't ruled out the injectors as well, however I have no idea how to test them. I'll be searching on that soon. They are the original injectors and as far as I know they've never been cleaned or anything.

 

Its prolly your injectors, I changed mine to Bosch III from Jon at FIC.
He got the best injectors on the market, he leaves 3 years warranty on them and he sells them for 169,95 (set of 8) flowmatched and they have a GREAT spraypattern.. Never got any better injectors then those, And I tested 4 different (Ford, Multec, Accel and Bosch IIIoo).. Bosch III KICKS ***!
never got better idle and throttle response, so Call Jon up at Fuel Injector Connection and he will help you out.