1991 volvo 240 distributor doesn't turn when engine is cranking.

I would try cleaning the Electronic Idle Air Control Valve with a trusted Electrical Cleaner then a Non-Conductive Lubricant.

The speed sensor or crank sensor as called by other vehicles is on the rear pass side. Follow a black wire that looks like a spark plug wire. It has a connector and 1 bolt where it attaches near trans. Well known for failing and no spark.

Chak the elektrical conections well on coils end sparkplags ..

SOUND LIKE BAD DISTRIBUTOR CAP AND ROTOR,SPARK PLUG WIRE ALSO COULD BE BAD.

Check if you still getting fuel and sparks, two items need to keep the car running. Check fuses and fuel pump relay, if needing new relays go to the junk yard and get couple of them for nothing. Checking making sure you getting fuel and fuel pump working properly, unplug the the main coil wire to distributor so the car wont start we just want the engine just to turn over. under the hood, locate fuel filter, disconnect the line to or from it, wrap the bottom of the hose with old clothe firmly and to remember to point the house downward away from your face so it wont splash at you. and have a friend turn ignition over just like starting, see if the fuel come out with good pressure. if fuses and relay check out, your crank sensor may be bad, being 91' strong possibility. crank sensor send info to computer telling to send fuel to your injectors. For sparks, make sure you plug the main wire to distributor back. pull one plug wire and get spare plug, plug it and ground the plug and have a friend turn the engine over and see if you getting sparks, do not touch the plug, big shock. No sparks, check the coil if you getting 12v, if yes, than your cam sensor is faulty. The cam sensor work just like the crank sensor but telling the computer to send sparks to the distributor. Common for older European cars, crank and cam sensor tend to become faulty after years of service due to age and heat abuse.

it is likely either the Crank position sensor, or the ignition module. (module is in the left front fender area behind the turn signal)

Did you replace the plugs? How hot is the spark from the coil thin and blue? if it is big and orange it is a weak coil and should be replaced. If it is good try an other wire from a different car (do not put a spark plug in it) and see what the spark looks like if good put the plug in it and check the spark again if this is a good the wires are bad

If you are sure about spark----there is an inline fuse on left front fender in engine compartment.If this is not it then get the Bently manual from IPDUSA.COM

Try a new engine rpm speed sensor. It is located at the back-top of engine block where it mates to trans. You will need to remove a single bolt (10mm socket or wrench). You may have to wiggle the sensor to lift it out. Another symtom you may experience, is when you are cranking the car to start, it will buck and act like it is out of time. Another possible component is the ignition power stage/amplifier.

You may want to remove spark plug to make sure you are getting a decent spark .a nice strong blue and usualy easily visible and not weak yellow spark thats hard to see .if you have a spare spark plug no need to remove one from engine.Make sure you have a good 12v source of power to the distributor.Is your distributor electronic?should be but if points based instead you may find its time to change the points.Also your coil needs to be checked by removing the H/t lead to the distributor and checking that the coil is producing a healthy spark.Coil and spark plug test is done while some one turns engine over while other person watches. while testing do not touch while cranking as you will get severe electric shock if you do .If coil produces poor spark check you have 12v into the positive terminal while cranking if that is the case the coil needs replacing unless the points are no good,if fitted and not electronic.Let me know how you go and if you have no luck starting glad to go further with help and advice