Volvo: 1993 940 Rough Idle After Starting, plug cap, cold start

Question
Dear Ray,
    I own a '93 940, no turbo, 190,000.  After cold start the engine idles rough, as if it's not running on all cylinders.  After a few minutes of warm-up the engine smooths out and runs fine.  I'm not sure where to begin to fix the problem.  Any ideas?  Thanks.  Don  

Answer
Don,
Next time starting cold open the hood and start the engine. As the car warms up carefully touch the exhaust manifold runners and see if there is one not getting as hot as the others that will be the non firing cylinder. Then inspect for spark and condition of plug, cap, rotor, and injector.