Idle rpm -vs- engine temp

["Mad Max"]

Peeps,



Does anyone else notice an idle rpm drop when the engine is good and warmed up? Most of my usual commuting is around town, 15 minute drives to work and back, etc. But this week I was towing the 28-footer and everything was well up to temp - engine/transmission both at ~180*, and when up to temp the idle seems to drop just a bit; add the A/C and it wants to lug. I end up placing in neutral and everything is fine, but I wondered if there is an engine management thing that is not working properly or if this is normal?



Obviously my idle setting is a bit too low - a slight nudge of the pedal and the rpm comes up just a hair back to my 'comfortable' range, and of course a slight idle screw twist and it'll be fine, BUT, why not when it's cold, and why when it's hot?



Tweaking the idle will increase the idle, but is there a bigger issue causing the problem? Thoughts from the congregation??



Muchas grassyas,



- M2

 

[Don Tanklage]

hit your ve with cold water (when it is at temp) and see what happens



i heard if it comes back up that it is time for a reseal



or hook a hot wire to your ksb and when it is hot flip the switch and it will idle just fine



don

 

[Midnite]

I don't know if it's what you're running into, but I had set the idle speed on my '92 to about 650 rpm. When we went on a trip through the lower 48, I noticed that when we were driving through southern Nevada that the idle was below 500. I bumped it up again, but as we were coming back up through the pacific northwest the idle was around 800 to 850. I spoke with Piers about it as we passed through BC, and asked him if the fuel temperature could be to blame. He said that was almost certainly what was happening.

I wasn't towing anything, but then in the 90+ degree heat around Las Vegas with the AC running, I didn't need to be towing anything to heat the fuel up pretty good. In slightly cooler temps, but towing, I can still see the fuel temp being a possibility in your case.

Mike

 

[Don Tanklage]

could be... .



but my truck has the stock tank and a aux tank (60 gals, polished alum, sitting in the sun)



after towing all day on the aux when i switch over to the stock tank (mounted under the truck in the shade) why didnt the idle come back up?

 

[bgilbert]

Normal, fuel temp and oil temp.

 

[Greenleaf]

Hitting a hot pump with cold water is known to sieze the plunger.

 

["Mad Max"]

Okay, sounds pretty much 'normal', and I think I will install a small manual throttle cable, just to up the idle a bit when necessary... much like on the old-school military vehicles... ... ... in fact, I think I just thought of where to get the throttle cable :-laf.

Thanks amigos,

- Sam

 

[Don Tanklage]

if you have the same style ksb that i do all you have to do is run a switched hot wire to it



tis easy





scott, that is just what i heard, the cold water test thing. glad i never tried it on my truck. i was worried about it cracking the pump body. those suckers get really warm. which is another reason why i question the "warm fuel - low idle" theory. maybe it is just that the pump is hot and has nothing to do with the supply fuel temp?



don

 

[Bob Beauchaine]

The book calls for the idle -with auto transmission - to be set at 750 - engine running - in drive with the A/C on.



Bob

 

[Don Tanklage]

dang!



set like that my truck will yank the front wheels when i take my foot off the brake!



lol



what does the book say about throwing the afc lever in the trash? or turning the fuel screw all the way in? or installing a s300 turbo and some 6 x . 020" injectors?



just kidding, i know you are just quoting what the book says...



tank



ps - ksb best thing since sliced bread (if you got the one that adv when energized)

 

[Greenleaf]

Yea, that is way too high for my taste. I set mine both for 800 rpm in "N" with a/c off. This sets it about 650/700 rpm when in "D" when hot and a/c is on.



You can set to your likening. The school buses have variable control for slow idle. The driver pushes on a button. It varies about 250 rpm's either way.