Rattling sound under hood at idle and low speed only

Idle adjustment procedure - Ford Explorer and Ranger Forums ...

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Mar 25, 2015 - 19 posts - ‎11 authors Idle adjustment procedure Under the Hood. ... Below are the stock idle speeds (RPM) for my 2000 SOHC V6 with strategy CDE4. ..... when you apply the throttle or it could be too much base timing causing a huge misfire. High Idle Blues 1994 4.0
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Does it sound like a valve or piston, or something loose on the exhaust pipe ?

These engines don't rattle and especially ping unless they are hot. And the sound of fluid thru the heater core. Tells me you are low on coolant. The engine is not cheap to replace.

1. Relearn the idle speed by disconnecting the EFI fuse and the ECTS fuse from the under hood fuse box. Leave the fuses out for 2-3 minutes minimum. Reinstall the fuses. Using your finger, push the throttle plates closed completely. Hold the throttle plates closed completely and have a helper turn the ignition switch on. Release the throttle plates as soon as the key is turned on. Reinstall the boot to the throttle body and start the vehicle. Allow the vehicle to idle for 5 minutes. Test drive the vehicle and check for normal idle operation.

the engine stalls. (i bet only on a hot engine, , am i right?)
this can be 2 things. but with this huge of engine 1.
the engine idle controls are not idling up.
or extreme, the engine is too weak and the compressor has issues.
does the car driver perfect A/c off? full power and normal hot
engines. and idle speed is at spec hot. near 800 RPM?
(spec, rpm is stated clearly on the hood sticker) open hood look up and under. see that EPA sticker, ?

if RPM is normal. hot.
the engine has huge power.
you turn on A/c and the rpm must not drop
did you try to push the throttle down to prevent the stall.
did that work> yes./no,
if yes,did the A/c belt squeal>?
if that cant work and belt does not scream, the engine has very low power.
the ECU increases idle speed when the A/C is on. this prevents stalls.
this can fail, if the ISC is bad. or diry.

It could be a leaking hose, and the PS fluid is dropping on the hot exhaust. Check the fluid level in the power steering reservoir. If low or dry, look for a leak.
I don't know about the rattling-better have someone look at it.

Remove EFI fuse 20 Amp from under the hood (engine compartment) for 5 Sec or more. Do the throttle body cleaning and relearn the idle speed.

I would check exhaust system for loose heat shields or bracket.

Sounds like time for a new engine to me. (severe engine damage due to oil loss or overheating)

I would check the operation of the idle speed control valve, it is what changes the idle speed when a load like the transmission is put on the engine, without it the engine will idle slow and stall out, this is even more apparent when reverse gear is selected or drive or the AC is tuned on. The ISC valve is located on the side of the throttle body top of upper intake manifold. Below is a picture of the ISC (idle speed control valve)