need help with crx, weird problem

[darccrx]

I have an 89 crx si with a b16a swap, straight flow exhaust and intake. recently had a no-start problem, but replaced the pgm-fi relay, and that fixed that, but now I have another problem... the car cranks fine, accelerates fine, and isn't throwing any codes. however, if I hold the gas in one place, or decelerate slightly, the car jumps and skips... then, if I nail the gas, it accelerates with no problem, as smooth as ever. if i let out the gas abruptly, it backfires badly, but if i kick the clutch in, it doesn't. I have an old crx with a d16z6 in it, so i'm not afraid to throw parts at it, I just don't want to waste time. anyone got a suggestion as to what it might be?

[superbluecivicsi]

plug inspection reveals? running rich? where did you put the o2 sensors when you swapped with the sir1? compression shows? timing is at?

[darccrx]

Plug inspection looks good, will be doing complete tune-up this weekend anyway. O2 sensors... only have one four wire on the exhaust manifold, don't have one at the cat, because I don't have a cat. could the lack of secondary 02 sensor do it without throwing a code? compression =good and timing was just checked and adjusted. the strange thing is that it wasn't doing this until yesterday. the no-start wasn't all the time, just intermittent, and it always ran great. After replacing the ignition for a mechanical problem, and the pgmfi relay, it started doing this. All the parts i'm pulling are from my old car, which was running perfectly two weeks ago. that's where the relay came from... could it have a problem? what should i systematically check? this is going to be all I do saturday, so i have time. obviously you know a lot more than I do... so give me some good newbie type advice. thanks