I have an automatic '99 LS that seems to be a little temperamental when it comes to shifting into overdrive.
I let the engine warm up before hand (enough for the RPM's to go down where they should be - anywhere from 1 min in the summer to 5-6 in the winter). But it seems like no matter what I do, it will not use the overdrive unless it's been driven for a while.

For a while I thought that it needs a little more ... weight to shift into overdrive. Every time when going to work for a good while, it was shifting into overdrive when going up a little bit of an incline on the highway. The same spot every time.

Then this changed though and now, i drive the car same 15 minutes to work every morning and i get there without the overdrive ever being used.

So my question is really: how does it decide to shift into overdrive? what's the mechanism that does this - could that be malfunctioning? Is there something i would want to look into replacing in order to make the overdrive shift happen all or most of the time?

I should mention couple things: after driving it for a while ... say after 1 h on the highway it's definitely using the overdrive then. Even though the weirdest thing started occuring: after about 5hrs of continuos driving, we stop for gas, turn the engine off and then when started back up and get on the highway - same thing, won't engage the overdrive.

I also had a carburated '88 Accord before, and i had essentially the same problem. Could it be a Honda issue that i'm not aware of?

Thanks much