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Weird ticking noise and idle speed changes

my 1993 5.0 liter bronco is making a strange ticking noise. when it’s idling, and it ticks, the idle drops. then it will tick again and the idle will raise up. usually between the 600 to 1000 rpm range. it just started doing this and never did before

Be specific re the conditions under which you hear this occur.

Is the ac on? if so does it do it with the ac off?

no, a/c is not on. when it’s in park, it does the most extreme idle changes from about 600 to 1000 or so. when in drive it get considerably less but i can still hear the ticking sound every couple minutes cause a distinct change in rpms

The idle air control valve doesn’t make any noise that can be heard from the cab with the engine running. That valve opens incrementally, stepping upwards of 60 times from dead idle to 1,500 rpms as I recall and the only clicking that would be coincidental to the idle speed suddenly increasing is the AC compressor being cycled on by a relay but you say the AC is off when the rpms jump. Where does the sound seem to come from? Possibly you can open the hood and listen to isolate the click.

it probably ticks at higher rpm as well, you just don’t hear it because of the engine noise. You check your oil?

thanks everybody, i figured it out. the guy i lent my truck out to broke the knob for the a/c when he tried to turn it on, not realizing it has not been charged. he stuck the knob back and i didnt even notice. i guess the clicking i was hearing was the compressor trying to kick on. never loaning my truck out again

I think the clicking was the relay for the compressor, and the engine had learned to adjust to the draw of the compressor on the system, but did not know the ac was not kicking in. Glad it was a cost free experience.

That guy you mentioned sounds kind of inconsiderate

A decent person would have said “Thanks for loaning me the truck. I broke your AC knob off. I’m sorry about that, and I’ll get it fixed.”