Okay, here's a strange one--

Gotta '88 Civic DX, and it was running quite well, but I noticed the head gasket was purging oil. So I pulled the head and changed the gasket, and that's where the ugliness began.

When you first start it, it idles too high, up around 2700 rpm. Then as it warms and idles down, there's this profound surge, almost like someone's sitting in it and goosing the accelerater in a very regular, rhythmic pattern. When it's totally warmed, it idles smoothly for a couple of seconds, then almost cuts out, very sharply, then goes back to the couple of secods of idling. This weirdness is also very rhythmic.

I notice that if I unhook either the MAP sensor OR the throttle positioning sensor, the car will idle almost normally and run fine. Except that the mileage is horrific. I also notice that if you've just started the car at night, there seems to be something electrical going on...the car will do the surge thing, but mildly; when it surges up, the dash lights dim a little, then when it idles down, the lights brighten again. In a rhythmic fashion, of course.

So, what did I do when I pulled the head? Must be something simple. It always is. Anyone have any insight?