Ol' Navy

What RPMs is a 1991 4.9 l6 supposed to idle at? I mean the lowest possible RPM that is safe, and I also would like to know how to adjust it, with detailed description lol. Thanks.

unit505

Auto or manual? Ac or not? No ac at the moment with my 5 speed idled at 900. You can look at the front of the throttle body and see where the linkage rests on a screw. That screw is the idle adjust up or down. I'll take a pic in a minute and post it.

Ol' Navy

Auto and I don't really know what my idle speed is because I just now was wandering a bout this, so I was just wandering what the safest lowest would be when the AC is off... and of course with AC on it owuld shoot the rpms up wouldnt it?

unit505

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the ac will load the engine and pull the rpm down. I'd say 1000-1100 rpm with ac on.

Ol' Navy

And where exactly is that? And which way do I turn it and what is a safe rpm number?

Welder7018

Right raises idle left lowers it. Mine idles at 1k

Ol' Navy

Ok do I crank the truck then turn the screw to the left until its at the proper idle speed?

unit505

If your going to tackle this, you gotta know where the throttle body is. Where your intake tubes hook to the engine is your throttle body. You can't miss it.

unit505

Gotta be cranked.

Ol' Navy

Oh I didn't know for sure it was on the throttle body. Thanks guys.