Does high idle consumes more gas??

If it idles high, with it in park, block off mouth of throttle body with something, it should kill the engine. If very little or no effect on idle, you have false air getting in there from somewhere.
Make sure throttle valve is closing, where applicable, take throttle cable loose, see if idle returns to normal. Check and clean idle air system. Any applicable trouble codes?

have OB scan run, even if there is no light on (check engine) it should narrow your choices

"Could this be a throttle positioning sensor problem?" - probably not. The Throttle Position Sensor (TPS) tells the computer how hard you are stepping on the gas. It does not really control idle speed.

Your problem is more likely the Idle Air Control (IAC) valve. This is a small electric valve that the computer can open and close in small steps to set the idle RPM at the desired point (a little higher when cold, then down to normal speed when warm). The IAC valve is notorious for getting all crudded up inside. Then it sticks open too much (really fast idle speed) or sticks shut (really low speed).

You can try taking it off the engine, cleaning it with carb cleaner spray, and putting it back on. That is easy and cheap.

If cleaning does not fix it, you need to buy a replacement valve and put it on. Pretty easy to do but costs more $$$.

Is it the engine vibrating or the car? If its the car itself it sounds like u need to have the tires checked & balanced.

Kristie, you need to do some maintenance ! start w/ basics, replace air & fuel filters, a must do ! good time to replace spark plugs & plug wires ! also replace distributor CAP & ROTOR ! see how this does, there could be more . some of your sensors may need replaced ! I don't know what you have done, if anything lately, so, you may want to replace the OXYGEN SENSOR, ALSO, you may need to replace both the CAM & CRANK SENSORS !!! IF you take your car to an autoparts store, they can see if your computer has stored any trouble codes !!! do that first, then , change your filters , and so on !!!

It can be issue with IAC( idle air control valve) causing the problem.

There are many other possibilities causing these idle issues. Engine idles rough.

There are few help links with solutions to troubleshoot such idle issues.

I suggest you refer the link below and follow its troubleshooting details:------

Click the link below:-----

Ford Expedition IAC valve replacing

http://technoanswers.blogspot.com/2012/12/ford-expedition-iac-valve-replacing.html

Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

-----------

Stumbling and stalling at idle after engine rebuild?

http://schematicsdiagram.blogspot.in/2012/03/stumbling-and-stalling-at-idle-after.html

------------

1999 Ford F-150 Idles rough and quits when gas pedal is pressed less?

http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html

---------

Engine stumbles coming off idle when warm?

http://repairhelpcenter.blogspot.com/2012/01/engine-stumbles-coming-off-idle-when.html

------------------

Erratic idle on car?

http://schematicsdiagram.blogspot.com/2011/12/erratic-idle-on-car.html

-----------

Cold start problem and vehicle shudder around 2500 to 3500 rpms

http://repairhelpcenter.blogspot.com/2012/10/cold-start-problem-and-vehicle-shudder.html

----------

Low idle when cold out side?

http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html

-----------

GMC Sonoma Stalls and idles low

http://technoanswers.blogspot.com/2012/10/gmc-sonoma-stalls-and-idles-low.html

--------

GMC Idle Air Control (IAC) Valve Replacing?

http://schematicsdiagram.blogspot.com/2011/12/gmc-idle-air-control-iac-valve.html

-------------

1996 Camry intermittent engine failure while idle?

http://repairhelpcenter.blogspot.com/2011/10/1996-camry-intermittent-engine-failure.html

------------

Engine quits at idle?

http://repairhelpcenter.blogspot.com/2011/10/engine-quits-at-idle.html

-----------

Car overheats and Air blows hot at idle?

http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html

---------

High Idle Problem

http://repairhelpcenter.blogspot.com/2012/10/high-idle-problem.html

-------

While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

---------

Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed?

http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html

--------

High rpm in neutral? Inconsistant high RPM in neutral?

http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html

-------

Vehicle stumbling at idle and shows code 54?

http://schematicsdiagram.blogspot.in/2012/03/vehicle-stumbling-at-idle-and-shows.html

----------

Rough idle, staling and Erratic shifting?

http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html

-----------

While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

---------

These details will help.

Thanks.

Idles low or high ?
Ford idle air control valve IAC test stalling problems

Absolutely!. The dealer shafted you, if he told you nothing was wrong. 80 psi leakage out of exhaust (valve,;;;where else?) is a dead give-away: You need a good old fashioned VALVE JOB. Your exhaust valve, see, is not seating properly, not sealing as it should. It leaks, bigtime in your case, so compression is low, unburned gas escapes out the exhaust (You smelled it!), no power from that cylinder so it idles like ****, and will try to die, and of course, mileage suffers. Sound familiar, Robin?
Now of course the dealer knew what it was. Apparently he didn't want this time-consuming job. All he wanted was his in the door and out money. From the shop mechanics point of view, a cylinder head job is a relatively low paying and time consuming job. But there's no excuse for somebody not telling you that you need a valve job. Take it somewhere else. It's gonna be expensive, no getting around it, cause the head has to come off, but at least it's a whole lot less than an engine overhaul. And just give those figures to your new mechanic-the diagnostics are all done. Good luck.

o2 censere

It's easy to overlook but a bad clutch fan will cause overheating in stop & go traffic, while you're idling or out on the trail at low speeds. When you rev the motor, you should be able to hear the clutch fan 'roar' up to speed slightly behind your engine speed. It's a noticeable sound when it's fixed, but ya don't pay any attention to it if it has slowly gone bad... other than wondering why you're overheating.
CHEAP "FIX" #1: If your clutch fan is known to be bad, you can remove it and drill two small holes in it where the internal spring is located and put two sheet metal screws in to make it 'lock up' all the time. Put these 180* apart, directly across from one another to keep things balanced. Upside: .20 cents to fix. Downside: Reduced gas milage with it going all the time.
CLUTCH FAN REPLACEMENT UPGRADE: Pull out the clutch fan and use it to enhance your garage wall. Instead of putting in another clutch fan, you can free up some horsepower when you install another electric fan for primary cooling