I need diagram for evap system for 2003 Ford

Diagrams here

https://www.google.com/search?q=2001+Ford+Taurus+24+valve+doh+firing+order

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All 2003 Ford vehicles were shipped with vacuum line routing diagrams printed on a sticker, which should be affixed inside your engine compartment. It is important that you use THAT diagram, as vacuum routing varies widely from vehicle to vehicle depending upon options and regional configuration.

The code is for the idle air control valve which controls idle speed.
The problem could be a faulty control valve, or a vac leak which is letting in air to the intake and bypassing the control valve.

No Idea what is leaking until you tell us

Well, there are actually two different 3.0L engines used in a 2003 Mercury Sable. One is an Overhead-Valve (OHV) type engine. The other is a Dual Overhead Cam (DOHC) 24-valve engine. You can tell the difference by just looking at the engine or by checking the 8th digit in your VIN. For the OHV engine the 8th digit of the VIN will be a "U" and the DOHC engine will be an "S".

This is important information when it comes to getting parts or information for your vehicle.

Anyway, I have provided belt routing diagrams below for BOTH of these engines.

P0457 FORD - EVAP Control System Leak Detected (Fuel Filler Cap Loose/Off)
EVAP control system has a very large leak such as fuel filler cap fell off, EVAP control system does not operate properly.

Vehicles that meet enhanced evaporative requirements utilize a vacuum-based evaporative system integrity check. The evap system integrity check uses a Fuel Tank Pressure Transducer (FTPT), a Canister Vent Solenoid (CVS) and Fuel Level Input (FLI) along with the Vapor Management Valve (VMV) or Electric Vapor Management Valve (EVMV) to find 0.040" diameter or larger evap system leaks. Federal vehicles can utilize a 0.040" leak check rather than the 0.020" leak check required for California vehicles (click over pic for zoom).



Symptoms:
- Engine Light ON (or Service Engine Soon Warning Light)
- Possible a noticeable fuel odor caused by the release of fuel vapors

Possible causes:
- Missing fuel filler cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap

Possible solution:
- Retight or replaced fuel tank filler cap

Tech notes:
It is a very common problem with Ford vehicles. There are service bulletins for the following vehciles:
1997-2000 Ford CONTOUR
1997-2002 Ford ESCORT
1997-2003 Ford CROWN VICTORIA, MUSTANG, TAURUS
1998-2003 Ford ESCORT ZX2
2000-2003 Ford FOCUS
2002-2003 Ford THUNDERBIRD
1997 F-250 Ford HD
1997-1999 Ford Ford F-250 LD
1997-2003 Ford E SERIES, EXPEDITION, EXPLORER, F-150, RANGER, WINDSTAR
1999-2003 Ford F SUPER DUTY
2000-2003 Ford EXCURSION
2001-2003 Ford ESCAPE, EXPLORER SPORT TRAC, EXPLORER SPORT

Also, in this link could check this Ford Bulletin.

Hope helps (remember to rate and comment this answer).

You have to remove the upper intake manifold.

2 things
cooler pluged;
converter is overheating

http://www.daycoproducts.com/daycoweb.nsf/DaycoSerpentineBeltGuide.pdf
i belive it is illustration 5-7

Here is a diagram