Engine Fuel mileage concern

[a6falcon5]

Fuel mileage
I have a 1988 LX NB and I'm getting about 12 MPH. Its stock with a 5 speed, the temp gauge moves a 1/4 of the way up at operating temp. I runs great but after driving a while and it's turned off and restarted it won't idle for a few minutes maybe 2-3 then it comes back and runs fine again. I just noticed it idling at about 1200 rpms and fluctuates down to 1000 and back up. Any suggestions would be greatly appreciated.

 

[Bill Gordon]

What axle ratio are you running?

 

[castine917]

What thermostat?

 

[Maryland Stang]

What's NB? Never mind. Notch back...

Have you checked for any codes? That's always the first thing I look at.

 

[Mustang5L5]

#1) Codes

#2) driving style


Despite guys claiming 30 MPG on their fox, i've never managed to do better than 15-18MPG with my car and i keep it in excellent condition. 3.73's prob don't help

 

[ThatBear]

#1) Codes

#2) driving style


Despite guys claiming 30 MPG on their fox, i've never managed to do better than 15-18MPG with my car and i keep it in excellent condition. 3.73's prob don't help

When I had my freshly rebuilt 306 with h/c/i I was getting 15mpg during break in and 25 afterwards. Ofcourse I just drove it to and from work and slowly because there's alot of deer on the roads at 3 am. That just shows its all about driving style

 

[88LX5.Oh]

Search for the surging idle checklist and dump the codes too.

 

[a6falcon5]

What axle ratio are you running?

Stock

 

[jrichker]

See the "Surging Idle Checklist” for help with all your idle/stall problems. You can guess at the problem and throw parts at it, or you can use the checklist to help you find the problem quickly and inexpensively. The checklist is right here in the Stangnet 5.0 Tech forum and you don’t have navigate to some other unknown web site. It‘s free and doesn’t cost anything: at last count there were more than 103,000 visits and still climbing

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.