Pulsating RPM's and lights and now dead!

'95 Accord V6. When it gets cold (sometimes) the rpms will go 500 to 1000, 500 to 1000, over and over while at idle. You can drive the car just fine. The lights (headlights, interior lights, tailights, etc. all of theml) will pulsate from low to high in sequence with the rpms going up and down. Tonight, while it was doing this, we shut the car off and now it won't restart. Lights are bright so battery is not dead. When I turn ignition, I get no sound at all. help? please?

UPDATE!

Just went back to pick up car and get it back home (300 yards away) and it cranked right up. No Fluctuation. Everything normal. ANy ideas?

Bad ground. Check cables for corrosion or looseness.

Why would a "bad" ground only show up in freezing weather?

It happens. Thermal reaction of metals invoved in the contact, would be my guess. Seen it on lots of vehicles with a myriad of problems.

Or it might be something else completely. Just put me in mind of a couple I've seen behave similarly when a negative battery cable clamp cracked or a battery to chassis ground corroded up.

From your description it sounded as if there was adequate contact to the chassis ground, but perhaps not the engine ground. I'd check that first.

I may be way off track, there might be something else common to your model that can cause this, but after 25 years in the shop I've found that verifying contacts and grounds before chasing weird electrical problems will save you loads of cussing and headbanging later...

Good luck with it.

assuming the car does not crank and the battery and alternator is still good, check all fuses and battery terminal connections.

I noticed the ground on the battery was slightly loose. I tightened it up and it looks like things are okay. I guess it makes sense that it gets loose, car runs strictly off alternator. THen when you cut it off, it won't restart until you get out and shut the door or wind blows the car just enough to make the ground connection good and then we get ignition!! Make sense?

Sometimes just the slight temp change when the car isn't running will change the cable's flex just enough to slightly move the contact area if it's loose....

If a cable is barely connected, the contact point is so small, it's carrying an enormous amount of electrical load through a pinpoint area, then at somepoint it cannot carry the load anymore due to heat, and if it can't arc and grab a new connection at a different point, the connection shuts off like a switch from high temp resistance. then you start running off the alternator. When you step on the gas, the slight change in voltage and current can then overpower the resistance and jump to an alternate point of contact, but at idle it finds itself unable to find a ground again.

All this activity in the cable and terminal causes abnormal heating of the materials that will change the cable's shape slightly, and relax when it cools.

Talking about loose battery connections---it is sure way to blow your ECU/Transmisson computers due to overvoltage from the alternator. The battery acts as a sufficient load to the alternator and if the connection is loose, the alternator can overvoltage and blow those units plus others. Always keep the posts and cable connections clean and tight. It is a good idea to use a battery anti-corrosive paint or anti-corrosive donuts on the terminals.

Talking about loose battery connections---it is sure way to blow your ECU/Transmisson computers due to overvoltage from the alternator. The battery acts as a sufficient load to the alternator and if the connection is loose, the alternator can overvoltage and blow those units plus others. Always keep the posts and cable connections clean and tight. It is a good idea to use a battery anti-corrosive paint or anti-corrosive donuts on the terminals.

Yup, the battery acts as a capacitor to absorb surges in voltage and current and dissapate them before it damages sensitve electronics. Good point.