All of a sudden our 91 740 4 cyl began starting/idling rough when cold. Once warmed up it idles alright but still slower than normal. Ideas?

check the OBD for codes. i'm going to go with it being the IAC. sometimes cleaning it won't do anything because it's actually completely broken. i HAD to replace mine. and it wasn't cheap since i have a rex/regina system.
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Ken
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'

I would start with your idle air control. The FAQ has a picture (I think) and it will just slide out of its rubber mount, making this the easiest thing to work on. This is also something you should check if you have noticed oil in the intake hoses, but that's not a sure thing by any means.

I would also clean your throttle body. Carb cleaner will work, brake cleaner too, or a semi-soft brush (read medium toothbrush). This is only .. ahm 3 nuts and the intake hose to remove, and it can be cleaned while it's got its vacuum lines attached. This should be noticeably sooty and gunky if you take it off. The outside might be sparkling clean, but the inside is not necessarily.

air filter, dirty injectors, all sorts of breather problems, but I would start there.

Do you have any diagnostic codes? see the FAQ for instructions on getting them. I don't know if an 86 has it, but my 90 does.

good luck,
Will
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1990 740 Turbo, on its way to stock specs, maybe beyond

I'll second the IAC thought.

Pull it out, spray some throttle body cleaner in there and plug both openings with your fingers, shake the cleaner around in there, dump it out, repeat. Do this five or six times and then give it a good rinse utilizing the pressure of the throttle body cleaner spray can.

In the winter I also like to bring it inside and warm up before I put it back in there so there's less fluid to freeze up after it goes back in.

I would also suggest removing the plastic idle adjust screw and housing and giving them a good cleaning. It's attached to the throttle body by a couple of screws.

Could be bad O2 sensor, engine temp sensor, intake manifold/tubing leak, dirty air filter, bad idle air control valve, ...