LM Mos2, perhaps, lowered my Idle speed.

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I had driven ~1000 miles to the eclipse's path of totality in two days. I checked my oil level when cold out in the middle of nowhere and found it right in the middle, having started at about 3/4. It should have been reading a little higher than actual, as The Vehicle was slightly nose down at the time, so it had burned some on the drive.

I thought I had a spare quart of M1 0w-40 but all I had was a can of LM MOS2 that was half MOS2 and half TDT 5w-40 left over from a previous oil change.

While I knew I was in no danger of it running too low, Warm and fuzzies required I add it. Next day when hot, I noticed the engine was not idling quite as smoothly as normal, as normally I can't notice it.

Then I looked at my tach, and while the factory service manual says it should Idle at 750 rpm, for the last 7 years since I added the tach it has idled when hot in gear foot on the brake unmoving, at 525 to 550 rpm.

It now Idles at 500 rpm hot in gear foot on the brake unmoving. As hot as it gets, I have 22 to 24 PSI oil pressure at this 500 rpm with M1-0w-40. 65mph at 1900 rpm is 50 to 54PSI. Max cold is 68PSI, max PSI hot is 62 at 2400+ rpm.

It is a 1989 throttle body injected 318 controlled by the engine computer.

I am not saying the MOS2 lowered my Idle speed rpms nor claiming any magical properties of the product, just that the hot idle speed rpms in gear have lowered by 25 rpm after adding it. I am aware there could be other affecting variables, it just seems to have some rather direct correlation.

I expected the engine computer hold whatever Idle speed it decided to, and remain constant.

I know M1 0w-40 requires no additives and in general I am not an Additive type of person. I Noticed nothing when I bought and added half a can of the Mos2 3 years ago and added it to M1 0w-30 AFE, and forgot I had half of it left.

Average Fuel economy over the 2500 miles was pretty good for my Vehicle considering all the considerable elevation changes, before adding the Mos2 and Afterwards as well, Exceeding my expectations by ~0.5 MPGs for the ~2300 miles I acquired before the last fill up.
 
I don't see how it could have affected the idle speed. I believe it was caused by something else.
 
When was the last time you cleaned your throttle body/blade? The idle speed is not electronically regulated on your engine and a carboned/gunked-up throttle body/blade will cause an idle speed reduction.
 
I looked down the TB's throat about 10 days ago before road trip. No obvious varnish.

Perhaps My Idle speed actuator motor is retracting a bit further. The thing has always been noisy.
 
Originally Posted By: zrxkawboy
I don't see how it could have affected the idle speed. I believe it was caused by something else.


Me either. I'd call it a coincidence, and there's some other issue, either with an electrical part, something mechanical, or a vacuum leak.
 
Originally Posted By: wrcsixeight
I looked down the TB's throat about 10 days ago before road trip. No obvious varnish.

Did you just glance at it or open the blade to look behind it? Usually the varnish hides behind that blade. At least that is how it's been in my vehicles. Spakling clean on the intake side, varnish and oil on the manifold side of the blade.
 
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