93 deville burns alot of fuel, like a gallon a mile; no leaks in fuel line. Any suggestions?

I dont think there is a connection between an oil change and the gallons per mile.
With that age car, I suggest a Terra engine clean. It will blow away nine years of gunk from the spark plugs, fuel injectors, cylinders and exhaust. Should give you more power, more miles..

the fuel pressure regulator will not do it. you need to look at spark plugs ,wires ,air filter, fuel filter. tires pressure if tires are under pressure can cause bad gas mpg

prob. a fuel line leaking

check for a leaking fuel rail,or injector,or the fuel pressure regulator,which is a vacuum operated valve at the end of the fuel rail.the high idle is caused by a vacuum leak,and if the regulator is leaking,that could be the fuel smell

remove fuel line from fuel rail end and put switch to on position let some fuel come out from line, then replace fuel filter, check oil if any water marks in oil if not fix fuel rail line back you are readu to use it normal.

if you can smell fuel then something is wrong. if you smell it only out of the tailpipe then if there was a problem the check engine light would be lit up. raw fuel could be leaking at a fuel line or component and unless is severe would not cause a engine light.you didnt state what your mileage is your getting but alot of things cause poor mileage number one is driving conditions and habits.you can increase gas mileage more than 15 miles to the gallon on alot of cars just by paying attention to driving habits. also it is important to clean the throttle body regularly. a dirty one causes all kinds of problems and low fuel mileage is one of them.it needs to be physically cleaned,no in tank treatment or additives will do the job.if you take to a shop make sure you see a tech taking of air intake tube and cleaning it with some sray AND a brush. some shops just put additives in the gas and oil and sometimes in a vacuum hose or throug the fuel rail.it is an inexspensive service [when not included in a fuel injection cleaning package] and should be done at 30,000 miles or sooner depending on drive conditions etc.

look at the fuel lines and injectors for signs of leakage.

go to Dollar Tree and buy a $1 Fuel injector cleaner. pour that in your gas tank and fill up with PREMIUM, 92 or 93 octane. Most times its cheap gas (regular). Premium will get you 5 more miles per gallon and alot more power.

At each 100,000 mile interval u need to replace the spark plug, at 30,000 the air filter and fuel filter, check the cooling system hoses and coolant every 60,000 miles, check the drive belt every 30,000, replace after 60,000. These are routine suggested maint items.

And don't forget to keep the pressure correct in the tires, under-inflated tires kill fuel mileage.

hey
at the begging u should clarify how many gallon u used.
112 miles at 28 miles per gallon --> 4 gallons burned (112/28)
So that means we leaked 11 - 4 = 7 gallons

Now figure out how long the car was driving.
112 miles at 64 miles per hour --> 1.75 hours

So, leak was at a rate of 7 gallons in 1.75 hours
7/1.75 = 4 gallons per hour leaked.