Loud hissing sounds comming from the intake followed by rough idle then stalling. Not an every time deal,but about 80% of the time

A vacuum leak in the intake manifold of a 2000 Ford F150 4x4 with a 4.6L engine and automatic transmission can cause a range of symptoms, including:

1. Rough idle: A vacuum leak can cause the engine to run rough at idle, which may be especially noticeable when stopped at a red light or stop sign.
2. Misfires: The engine may misfire or hesitate under load, such as when accelerating or climbing a hill.
3. Poor fuel economy: A vacuum leak can cause the engine to run lean, which can result in decreased fuel economy.
4. Check engine light: A vacuum leak can trigger a check engine light, which may indicate a code related to the engine's fuel system.
5. Stalling: In some cases, a vacuum leak can cause the engine to stall or die, especially at idle or when coming to a stop.
6. Hissing sound: A vacuum leak may cause a hissing sound to be audible from the engine compartment, especially if the leak is large or near the intake manifold.

If you suspect a vacuum leak, it's important to have it diagnosed and repaired as soon as possible, as it can cause damage to other engine components over time if left untreated. A mechanic can perform a smoke test or other diagnostic procedures to locate the source of the leak and repair it as needed.

You may have a vacuum leak at the intake manifold or other vacuum source, follow the link.

https://www.autocodes.com/p1138_ford.html

Check for broken breather hose from valve cover and follow it under the intake. You may also have a ruptured diaphragm crankcase ventilation valve (vac leak), bolted under intake manifold.

time tu du some regular maintenance--the squeal probly a worn belt--affectin the alternator -hissing sounds like a vacuum leak--chec all hoses--also inspect ignition wires and distributer--buy a haynes repair book in a partsplace-detailed for the homemech

http://groups.yahoo.com/group/villagerquest/

SHOWING MISFIRES ON SCAN TOOL?IF NOT,ENGINE CONTROLLER HAS NOT LEARNED MISFIRE MONITOR..WILL HAVE TO BE DRIVEN A BIT FOR RELEARN..IF YOU CAN SEE MISFIRES..MISFIRING ON MORE THAN 1 OR ALL CYLINDERS?CHECK UNDERSIDE OF IGNITION COIL FOR CRACKS..IF NOT CRACKED,YOU MAY HAVE A FAULTY CRANK SENSOR..ANY CORRODED PLUG WIRES AT DISTRIBUTOR CAP?ALSO CHECK IF ANY OIL PRESENT IN INTAKE MANIFOLD..GASKET ON BOTTOM OF INTAKE MAY BE BROKEN CAUSING AN INTERNAL VACUUM LEAK

there are 2 things that usually cause this, one is a dirty intake idle control valve and the other is hard engine mounts, I would say that both most likely apply to your car. try cleaning the intake with the following procedure from Ford.
Here is the most common cause of surges and stalls and low idle rough idle, it is the idle speed control air-bypass valve and throttle valve (IAC for short), they get full of gunk over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

Check the EGR for leaks.Here is th emost common cause of idle surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake

Hey Neil, try here,,
http://www.fueltech.net/downloads/download/110/ft350-ft400-manual

vaccum leak