1996 ford bronco 5.8 litre, auto, engine idle has

intake air control valve,map or maf sensor.pcv valve or leak from vacuum hose.damaged or perished air box to throttle body pipe

Check for vacuum leaks & if you find none,
have the entire vehicle smoke tested for leaks

You have unmetered air coming from somewhere

remove and clean or replace IAC (idle air control)

Not sure about the tach, but the link should give you ideas to check on.
Do It Yourself Diagnosis and Repair

have the oil pressure checked. i believe the specification is 40-60 psi at 2000 rpm. sticking valves and lifters can cause valve train noise. weak vavle springs can also be the problem. try running an engine cleaner such as gunk motor flush at your next oil change. follow directions specifically. obtain a product designed to aid in cleaning deposits on valves.

Check the rpm gauge while running. If the RPM needle fluxuates while idling that is caused by a defective spark plug and or a spark plug wire

Your truck is OBD2 compliant take it to a local auto parts store and have them read the code for you they usually do this as a free service, if it doesn't have a obd2 port then your truck is not a 1996 vehicle.

The idle is controlled by the computer. if your idle has been getting worse you may just need to remove the air tubes and spray the intake with carb cleaner. Rev the engine some while doing this so it wont die.

run scanner for trouble codes, some auto parts stores will do this for free

Hi,

Offhand, yes this would be normal. The high idle is brought about by the auto choke whose purpose is to hasten the reaching of operating temperature of the engine. The fact that the idle RPM goes down after some time is a good indicator, it tells us that the auto choke is working.

Just a start, do postback how things turned up or should you need additional information. Good luck and Thank you for using FixYa.