So my mustang has been in storage for the past winter. I took it out a couple weeks ago and my gas mileage has seemed to drop considerably. I used to get 15 mpg city driving conservatively but after I took it out of storage, I went through half a tank of gas in 55 miles driving conservatively. I just changed the fuel filter and did a oil change and noticed no difference. Any other ideas? Car only has 30,000 miles and is a 4 speed auto.

 

maybe the gas went bad? How long was it in storage?

 

from november to a couple weeks ago. I topped the tank off but before doing that, I burned the old gas out till the low fuel came on (stupid, I know.) I just changed the fuel filter a couple days back too. I even called the gas station to see if they had bad gas and they said that their gas pumps would turn off if they had bad gas.

 

forgot to add that when i start it up, it jumps to 2000 rpms and then stays at like 1400-1600 till i shift it into reverse. After shifting, the car just "launches backwards". Yeah so it idles high too.

 

I think someone else on this 4.6 forum had the same problem about leaving it in storage awhile. maybe you have to just drive it more and it will get back in its niche...

 

first step should be to reset the ECU. leave the battery disconnected for 10 minutes or so, reconnect, start up let idle for 10 minutes, drive around. see if that helps at all...

 

How would that help? Doesn't that just reset it making your gas mileage worse until it "learns" how you drive?

 

the ecu doesnt learn how "you" drive it learns values based on variables such as temp.

reseting the ECU should always be the first step i diagnosing something, as its extremely easy to do and practically free.

when you said the idle RPMs are at 2000, is that all the time? or after you shift/get car warmed up does it go down?

basically what you need to do, is eliminate any and all variables that you can. try getting gas somewhere else, preferably at a reputable chain. i've gotten bad gas even on a military base, infact thats where i've had the most problems, so i no longer go there and only go to 1 mom/pop shop, or shell/sunoco.

edit: btw, you didnt change anything before or after storage did you? do you notice more of a gas smell from your car? no Service engine soon light?

 

I put some new wheels and used tires on and my car started going to the left. (need alignment). The tire psi is at 35 all around so i dont know what the problem could be. When I start the car up, it jumps too 2000 and then hovers around 1500. But when i am driving, it'll drop to the normal 700-800. I've always went to the BP gas station down the street as well.

 

Idle speed issues are almost always IAC valve related, with an auto when you put it into gear the transmission loads the engine and when stopped can pull the idle down to a normal range--however during that time stopped the transmission is converting that high idle load, and the gasoline that is creating it, into heat.

Check the IAC and make sure it's doing what it should--unplug it with the engine at normal operating temperature and idling, the engine speed should drop; it may even stall.

If it does not, check the electrical resistance of the IAC coil, there should be 11Ω to 13Ω between the IACs terminal pins. If not the IAC is bad--replace it;

Then check from both pins to the IAC body, there should be more than 10kΩ resistance at each pin. If not the IAC is bad, replace it;

Next with the key on and engine off check the voltage between the red wire at the connector (unplugged) and ground, it should be >= 10.5V. If not there is a wiring problem that needs to be fixed or the PCM is bad...