Ok guys im new here. Anyways i have a 2004 cavalier and for the past few months this thing has been runing terrible and getting horrible gas mileage.
What ive done to it:
Brand new fuel pump and assembly.
New fuel Filter.
New ACDelco plugs.
New Delphi ICM.
New Coil Wires.
Brand new Magnaflow direct fit cat.
New injector o rings.
Full synthetic Mobil oil.
Had the tranny fluid replaced.
New air filter.
New upstream and downstream o2 sensor.
Checked all fuses.
Checked PCV.
Cleaned all sensor's and ecu circuits.
tested map sensor.
tested for vac leaks and found none.
THE CAR IDLES AT 500 rpm.
what is wrong with this thing. Also tested the alternator and battery.
New brakes.
I have nothing left to check or test.
Fuel pressure tested fine and compression is 150 across the board.
Someone have some input.
Im tired of getting 18MPG!

Also while pumping gas, if i hold the pump at full blast it'll kick off like the fumes aren't venting fast enough? I recently had pulled the tank and checked all the lines and connectors and everything is in the clear. Could that affect anything? Also is there a EGR valve on these?

is your car otherwise stock? larger rims, tire pressure correct, what transmission do you have, and have you changed the fluid (and filter if its and automatic)?

I was only getting 23-25 mostly city with the auto, HWY picked up well but I never had any long trips with it.

Car is completely stock besides the High Flow Cat. It is the 4-speed automatic. The tranny fluid was changed about a month ago, but didnt change the filter. Was done by Valvoline. Car has 140k miles on it. Would warped rotors cause gas mileage to suffer this badly? Tomorrow im going to remove the IACV and measure and make sure it is 1.1 INCHES. If not ill reset it. Im also going to check all the exhaust nuts and bolts, i think its missing 2 nuts on the manifold but it doesnt sound like its leaking at all.

be careful taking that out, sometime they break the the little wires on the sides. Valvoline did a trans flush, which isn't bad, but if that fluid is trying to push through a dirty filter, then it has to do a lot more work. if thats the original filter then it has to be pretty gummed up. not saying to will solve your troubles, but it couldn't hurt. also the machine that do the flush, put in how much they take out so if your a little low, you stay low. now if it were you you would def know it because the car would jerk its way through the gears.

I will try and replace the filter then. The tranny does act up from time to time. They didnt use the fluid exchanger on it. I used to work there and made them actually pull the plugs and do it that way. I also broke the other iac because i didnt know how to pull it out lol. Thanks for the input.

in order to drain enough fluid to do you any good, you have to drop the pan on that trans. the only plugs I know of are on the front which are for the cooler and the pump. then there is the fluid level check plug on the passenger side right near the axle.

Nick Davidson wrote:Also while pumping gas, if i hold the pump at full blast it'll kick off like the fumes aren't venting fast enough? I recently had pulled the tank and checked all the lines and connectors and everything is in the clear. Could that affect anything? Also is there a EGR valve on these?

the tank has to vent through the charcoal cannister during a refueling event. If the vent valve is stuck closed, blocked or partiall restricted you will have a slow fill. Any dtc's?

for the other drivability concerns; can you view datastream with a scan tool for:
-fuel trim
-iac counts
-iat and ect

So today i bought a multimeter and tested the IAT sensor. The connector is a perfect 5 volts. The sensor grabs continuity, but it jumps all over the place. Made me wonder if it was reading it and getting a bad signal. So i unplugged it and drove around. Wow! The car has power again. So i may buy a new MAP sensor and IAT and see what happens.

Can you describe how does the car rides? You get miss fire,hesitation?