I don't know how to put this, but I've suddenly developed a chugging/surging issue in my 99 Accord.
Let me go thru what I know first. On Christmas eve, I had to jump it off to start it, as the battery was close to dead, or dead enough to not start. We drove it up to my son's place for Christmas dinner (about 40 minutes away), then hung out for about 4 hours or so, then drove back. No issues. But when jumping it off, I noticed some green crap around the positive terminal, that I knew was probably not helping, and planned to clean it off. So, I disconnected the battery and put it on the charger (as I didn't know if it was down again or not) and cleaned up the battery cable end. The next day (after having the battery on the 2 amp setting overnight) I re-installed it, hooked everything up like normal, lit it off and put away my tools, as I needed to make a run to the Post Office. I got about a 1/2 mile down the road and it started the surging crap, then the CEL light came on and it cleared up. Get about 3 more miles down the road, and got caught by a traffic light, at the light the idle was surging between 1K and 1400 rpms. Made it to the Post office, did what I had to do, and on returning, the surging came back about a mile away from the Post Office. Then going down the road, it cleared itself again. Got back to the house and put my scanner on it. Came back as a PO181 code I think, High voltage to Coolant Temp Sensor. Now, I hadn't seen that code before in the 3 years I've owned the car. So, I cleared the code (I wanted to see IF it was going to come back or not). The CEL light is out, and I took my daughter to work Friday, the surging came back, but no light as yet. Would that be a bad sensor if that code comes back? Note; I haven't really done anything under the hood of this car, other than plugs, a valve cover gasket, and a timing belt. It was running it's usual self (very good) prior to pulling the battery, cleaning the cable end, and topping up the charge in the battery. I should add that I've had a CEL light on quite a bit with this car, mainly due to a PO1457 code (evap system), but it's never effected how it runs. I'm thinking I might have to get the Toyota out of storage and drive that, if I can't fix the surging.

 

Have the alternator and battery checked.

 

The coolant temperature sensor that sends the signal to the engine computer (PCM) is near where the upper radiator hose connects to the cylinder head. It is under the distributor and is the sensor that has 2 wires going to it. For a quick check, unplug that sensor and see if you have any corrosion on the electrical connector. Take a look at the wiring and the plastic harness to see if the harness is rubbing and has a worn spot on it. That could indicate an area where the wiring is damaged.

There is a sensor with one wire going to it, and that is the sensor that only controls the coolant temperature gauge on your dash and it will not affect how your car is running.

Take a look at your coolant temperature gauge when the car acts up. If you see a drop in that temperature, then you have 2 sensors indicating "cold" coolant and need to look at the cooling system.

The sensor is very easy to replace. I highly recommend purchasing the Honda part, because I am hesitant to use aftermarket parts.

 

Thank You for giving my a few places to check. I do know the temp gauge reading is normal when fully warmed up. I will look into it more when the weather warms up a little more (currently 33*F, and getting dark). Wednesday it's supposed to be warmer.
Is that what it does when the sensor goes bad (give a high volt reading to the ECU)?

Sean, I didn't forget you, and will check both the battery and alt, both running and not. I don't believe either is bad though. It was charging after I jumped it off, even with the green coated battery + cable end, and it was running like normal. I've just never had this issue arise just cleaning the terminal, and tossing the battery on the low amp charger. I really haven't really had to do much to this car over the years, which was the idea behind buying it. The biggest issue I have, is that I don't drive it every day, and it'll sit for up to a week at a time (I work from home now).

 

I haven't really had a chance to go looking for the problem yet, as it's been raining like crazy here. If not it gets pretty damn cold. I did drive it since I cleared the codes, and it did come back. It was doing it's surge thing, then the CEL light came back on, and it ran better again (almost like normal). I did a code scan after I got back, and the same code PO181 High coolant temp voltage came back. So it's something in that circuit. I finally got the Geo Prizm fixed (brake job, but waiting for parts held it up), so I can now nudge the nose in out of the wind.