RPM fluctuations at idle. Normal?

[239]

Since getting my scan tool, I’ve noticed that my rpm’s decrease and increase slightly in park, and in drive with the brake on. Does this happen to anyone else? It’s not a huge change, but they do move up and down by about 10 rpms every second.

This was over the course of a minute:

 

[974X4BLACKSPORT]

Yea, that is normal.

 

[poker4me007]

:

I think the rpms are okay also.
I'm curious do you have a lower temp thermostat (possibly a 180 degree thermostat) ?
If so what brand and how is it working for you?
Thanks.

 

[imp]

...... but they do move up and down by about 10 rpms every second........

A change of 10 rpm second by second is, IMO, a bit more than should be expected, if the load on the engine is not changing at the same rate. As a rule, I've noted pretty precise control of idle speed, unless sluggishness in the Idle Speed Control has developed. You might try cleaning the ISC (IAC, by some), and seeing if that tightens up the idle a bit. imp

 

[239]

I think the rpms are okay also.
I'm curious do you have a lower temp thermostat (possibly a 180 degree thermostat) ?
If so what brand and how is it working for you?
Thanks.

I’m running a Motorcraft RT1161 thermostat and it’s rated for 190 degrees. Which is weird because my scanner never reads a temp higher than 185, even on a hot Florida day. But that’s the only minor issue I have with it. My temp gauge stays at the half mark while driving and idling, and my gas mileage is great so I know it’s not running too cool.