gas mileage decrese? - Toyota Nation Forum : Toyota Car and Truck Forums

jordanangel · 03-28-2010, 05:14 AM

hey guys i have a 90 Geo Prizm with the 4afe engine and the 3 speed auto and was wondering why my gas mileage went down from 37 to around 25

I've been told its probably the fuel filter but i wanna know if that is it or if its something more

thanks ahead of time for your help

90 GP · 03-28-2010, 08:06 AM

How old are the plugs/ distributor cap/wires and air filter? Also could be a thermostat sticking that keeps it in warmup mode longer.

jordanangel · 03-28-2010, 08:14 AM

cap and wires got placed when i blew my pickup coil in the distributor and that's been replaced as well which was like 10-12k miles ago and plugs just got replaced like 5k miles ago cause the others were foiling on me and i also heard that it might be my thermostat seeing as its probably as old as the car and my car has 221k+ miles and as for air filter I think it needs to be replaced too and I'm waiting to replace that as soon as i get the money for a new intake and reusable filter

***REN69*** · 03-28-2010, 11:22 AM

does it idle higher than normal? if so it's the Tstat sticking open, so it keeps the car idling high to try and warm up, thus dumping extra fuel.

jordanangel · 03-28-2010, 02:03 PM

it idles rough some times but i think that's cause the alternator belt is not adjusted right so it squeaks for a time and slow the belt down too when its squeaking, the alternator has been replaced but still squeaks, maybe it does idle high and i don't know it

I'm gonna replace the thermostat and fuel filter and then see what happens

jordanangel · 05-23-2010, 05:52 AM

i replaced the thermostat and the gas mileage got worse

I just put in a new air intake with a new reusable filter

, so i know its not the filter, also the engine temp is not where I think its suppose to be, could this be a faulty thermostat that is sticking open or something else, hoping to replace the fuel filter soon, but haven't got the right wrench to replace it sadly

90 GP · 05-23-2010, 06:35 AM

Your lower temp gauge reading after stat install probably is trapped air in the system. The original stat has a small valve at top to vent air . You can check for air by parking car on an incline so front end is higher. With cold engine remove cap and set heater to high and run till car reaches operating temp. If you see alot of bubbling that is your trapped air. Top off with antifreeze and install cap. The engine not getting fully warmed up could keep it in startup mode longer which could decrease mileage. Your air intake could also affect your mileage. The original air filter box had a air temp sensor that probably insn't being used now. That lack of input may cause computer to get inmproper reading. Also check for stored check engine light codes that may not trigger light. Here is link:

http://www.troublecodes.net/Toyota/

jordanangel · 05-23-2010, 07:53 AM

are you sure i have that sensor, cuz i don't see where it would go and the only things connected to my old one were the MAF sensor and a vacuum hose, and do you mean run the engine with the radiator cap off? or just run the heater with the cap off?

90 GP · 05-23-2010, 12:51 PM

To burp air out of cooling system run engine(parked on an incline) with radiator cap removed. Be sure to turn heater to high to purge air from heater core at same time. I don't know if you have a california emmissions setup on your 4afe so it could be different from mine. My MAP sensor mounts on firewall with hose running to intake manifold. The air temp sensor( one I am referring to) plugs into a grommet on side of original air filter housing on the side and has a wire attached to it.

jordanangel · 05-24-2010, 02:08 AM

yea yours is different, and do you have the 4afe or 4age cuz i have the 4afe and they came only MAF sensored and the 4age came MAP sensored

I'll try the trick as soon as it stops raining