What could have caused this problem?

I had an odd issue with the wife's '00 Accord while we were on vacation last week. I'll be damned if I can figure out what it was, so I'm going to post it here, in the hopes that someone else can shed some light on the problem...

Coming down from the mountains on our way home, the car would occasionally have a "hiccup" if I backed off the throttle or quickly increased the electrical load (like flashing the headlights) - the tach and the speedometer (which apparently isn't a direct mechanical linkage :scratch: ) would momentarily drop to zero, the 'Maintenance Required' idiot light would briefly come on, and the engine would hesitate, like it had lost spark for a second.

Once we reached a lower altitude and filled up again with 87 octane gas (I didn't realize that Colorado's regular unleaded was 85 octane, and I did put half a tank of this in on the way up the mountains a week earlier), the problem went away. During the rest of the ~900 mile drive from Denver to home, the car never acted up at all, even with the cruise set on 90mph, the a/c blowing on full, the headlights on, and the radio blaring.

What gives? I'm stumped. I'd say bad/low octane gas, but I can't believe an OBD2 car designed to run on 87 octane would be that bothered by a little 85 octane. My only other guess would be the alternator is going, but I never experienced any issues with a heavy electrical load at lower elevations.

FWIW, it's a 4-cylinder automatic Accord, with about 65k miles.

Any ideas?

My first thought was alternator too. :scratch: Being that it resolved itself, I have to think something about bad gas, could there have been some kind of vapor lock caused with altitude changes, steep slope, etc. :scratch:

It could have been the computer trying to re-set itself for the denser air after coming out of the mountains...long shot of course...

Iain:

Here's another longshot for you: it could be a bad battery cable or ground strap.

My '88 CRX had a problem like this. It would die for a few seconds (everything electrical would go dead and the engine would bog) then be fine. During the latter stages it even sometimes acted like it had a dead battery, then would be fine later. The ground strap was almost corroded through. Later it started doing it again and replacing both battery cables fixed it (they were pretty worn as well).

Might be a bit esoteric, but just a thought.

Chuck