I used to have this problem in really hot weather only but it has resurfaced again and it's 30something degrees out here most of the time. The motor bogs under 1500rpm. It doesn't have power under 1500rpm and then it suddenly picks up once it gets out of that rpm range.
I need some ideas thrown out here to figure this out. I'm gonna check the ignition system today to make sure it's in good shape. It should be - I changed everything only a year ago and set the timing too (with the connector unplugged of course).
I changed the fuel pump only a week ago, and the problem came back after the new pump was installed. Why? Not enough fuel pressure? Or bad vacuum line somewhere causing the FPR to malfunction? I really dunno. I hate messing with the fuel delivery system. That's why I let the shop install the new pump.
The other problem is the rough idle. It doesn't idle smoothly at all when it's cold and still misses a little even when warmed up. Plus, the throttle response is absolutely crappy while the motor is cold and in open loop. I don't get much repsonse from a cold motor under 1500rpm (see above), and it doesn't react smoothly to throttle input. It all happens in jerks and spikes. Would a bad IAC motor cause this? The car had a bad IAC motor when I bought it and it displayed pretty much the same symptoms but they were far worse. The shop replaced the bad one with a junkyard motor. I would've gotten a new one but they already put this one in. BTW, the timing, IAC, and TPS and all within spec but the problems persist. Is throwing parts at the problem the only way of figuring it out?

 

Look into EGR valve...do a search, should comeup with some interesting findings. They tend to cause a lot of problems, such as ones you are experiencing. Also hook up a fuel pressure guage to eliminate fuel problem scenario. I think that will help eliminate the fuel delivery minus the injectors.

 

EGR has nothing to do with idle. Have you changed the fuel filter recently? How about the o2 sensor? Vaccuum leaks are another guess I would have. Maybe look to see if the plugs are fouled, or if a plug wire slipped off. Did you change the distributor or any parts in it?

 

EGR can affect idle...that is a fact. But, in rereading your post, I don't think it would cause your problem...but is a possibilty.

Vacuum lines a definite possibility.
The last I saw this type of problem occur someone had put in a new pump, and the pump was bad. I wouldn't know how to check for that, though...except to have a fuel pressure guage visible in your car as you drive it and watch for a drop in pressure.
Try cleaning your IAC motor, also.

 

I took the dist. cap off to have a look at the terminals inside and man were they crudded up. Some sort of powdery green buildup all over them. Anyway, I scraped off whatever I could with a screwdriver and then used my Dremel to clean the surface that conducts the spark from the rotor. After removing the buildup I noticed that the terminals were actually worn out and thinner where the spark arcs on to them. In other words, they were pitted pretty badly, some way more than others too. I figured that since I hadn't put more than 15000 miles on the cap I might as well clean it up and reuse it, but the motor started missing as soon as I started it up with the now clean cap. I thought first that it might be loose plug wires or loose plugs (I pulled the plugs to have a look at them - clean as a whistle and still gapped right), but everything checked out fine. I still had my old dist cap lying around so put that one on and the car ran perfectly fine. In fact, it now idles smoother than before.

Why did was the engine missing after I cleaned the cap? I made sure i didn't remove any material from the terminals. All I removed was the powdery green stuff. I didn't bother checking which cylinder it was that wasn't firing, but visually the cap seems fine. The terminals in the old cap that is now on the engine are actually more crudded up and worn out, yet it runs fine. What could be wrong with the new cap? Is it that the green stuff was helping conduct the spark from the rotor, but now since the gap b/w the rotor and terminal is too big the spark won't arc?

 

My vote goes to TPS.

If I could ever get myself away from my girlfriend long enough to get some sense into my head about getting my car finished, I'd have replaced mine long ago... I have a similar problem, but it's only on take off... I believe mines flat-spotted... you might wanna check yours for this too... I'd imagine an analog DMM would do this nicely...

 

The egr valve only functions when the engine is warm and at part throttle, although if it is left open at idle it acts like a vacuum leak. If the problem goes away when the car is idles warm, it is not the egr.

Are you sure you had the wires on correctly? It runs good now?

 

Yup it runs like a champ now, but the flat spot is still there. If it was the TPS, I believe it should have done this all the time. The problem used to show up in really hot weather and the engine would respond unusually slowly to throttle input. But it isn't hot here - it's pretty much freezing. I'll check the TPS anyway though.

On the dist. cap, is the new one screwed? That would suck because it was pretty nice Accel unit. Not like the old one has much left in it either. It's pretty badly pitted too. Talking about pitting, is it normal for the terminals to be worn away like that. I mean they don't come into physical contact with anything, they just pick up the spark from the rotor. Or is it a sign of a dying coil or something?