Runs great when warmed up though. It has been losing power gradually. I've replaced all the vacuum lines, turbo hoses, timing belt, plugs, wires, cap, rotor, fuel filter, air filter, etc in an effort to figure it out.

It starts right up, but every couple seconds, a cylinder fails to fire and it "hiccups." It hasn't ever actually died, but it's nerve-wracking. Especially since it's about to snow here in CO.

Seems the relays are OK to me, it's more related to engine temperature. Once it's up to normal operating temp, it purrs along.

Any thoughts about where I should continue troubleshooting? I hate to just throw parts at it, but I need it to run well during the winter. It's hard enough to handle on snow and ice without worrying if it's going to keep running...

My '91 N/A ran like crap when cold and wouldn't even start when it was below freezing when I first got it. Ran fine when warm. I could tell I had a bad fuel pressure regulator (fuel in vacuum hose) and was surprised that when I replaced that the cold problem disappeared. Can't explain why. Might be worth you checking your regulator just in case.
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Andy in St. Paul, '91 745 Regina 198K mi, '89 244 141K, '87 245 RIP

check resistance level for ECU temp sensor at ECU connector.(not sensor itself) See FAQ for ohms range.

Just to be sure, make sure your fresh air duct doesn't have any holes in it. My volvo ran like crap for a while only to find some holes hidden away underneath the fresh air duct -- easy to overlook. This messed up the AFM and therefore the computer. After replacing -- it ran great.

Thanks for all the responses. I'm going to head out there right now and give these three suggestions a try.