Your '89 740 GLE will have the B234F 16-valve engine. It is verrrry susceptible to idle and stalling problems if the throttle body is dirty, especially the throat area around the plate in the idle stop position. Drove me nuts until I learned to clean it every other oil change. If anyone has been adjusting the throttle body linkages, the idle stop screw or the throttle position switch then this will likely have made matters worse. Once that has been dealt with and if the problems continue then you may have a worn or sticky idle air control valve (also called an idle air control motor). You can try cleaning it (see the 700/900 FAQ feature section on this site), but replacement is sometimes necessary.

As for your car not restarting when it was hot, I can think of two likely things:
o The first is the rpm sensor on top of the bell housing behind the block. The original B234F sensors were known to be weak and are affected by heat. If the ECU doesn't see the crank turning over, the injectors will simply not fire. You can tell if you have the new and improved sensor by looking for a white ring near the electrical connector or checking for p/n 3547847. Even if you have the new rpm sensor, they can fail.
o The second is the injection system relay (also known as the radio interference suppression relay) under the hood may be going. Failure of this unit will again prevent the injectors from firing. They are also affected by heat. I'd lean toward this thought.

You should also check for any diagnostic trouble codes. Not all of them cause the Check Engine dash light to illuminate. See the FAQ for details on doing this. BTW You have an LH 2.4 system just like other engines. Transient codes may have been set, especially if the car has stalled at idle, so always read and clear the codes and allow them to re-appear (even over the course of a few days of running) before jumping to any conclusions.

If your car accelerates poorly or generally runs rough then:
o Check for air intake leaks. Check that the throttle body is bolted tight and carefully inspect for loose or split air intake hoses -the main air tube and all vacuum hoses.
o Check/clean/replace the ignition system plugs and wires.
o Unless you're an aggressive driver or spend a fair bit of time on the highway, the B234F runs at quite low revs and the plugs will easily get fouled. If this is a problem (like moderately heavy black carbon fouling seen at every oil change) you should clean your plugs regularly and maybe change to a slightly hotter plug or one with a longer nose -Volvo doesn't spec them so you have to know what you're doing (hint: NGK BPR6EVX).
o Before removing the plugs, inspect down the deep spark plug recesses. If there is any accumulation of oil at the bottom then your valve cover gasket is leaking -a tiny bit is okay if you mop it up at every oil change. The oil vapours can foul the exterior of the plug and the wiring. The B234F valve cover should be periodically re-torqued to 12 ft-lbs (11 ft-lbs for a new gasket) to help prevent this.
o Check for loose or nearly loose plugs. Depending on the plug used and how dry the threads were, B234F heads may not hold the normal plug torque (use 22 ft-lbs rather than 18 -be careful not to cross thread).
o Make sure you are using a quality 90+ octane gas [North American (R+M)/2 measure]. Lower octanes causes knocking which retards ignition timing. Noname brands will not necessarily have adequate injector cleaner additives. If you are going to run lower octane or cheap gas then you might want to occasionally use a quality injector cleaner gas additive (like pure Techron) and try re-torquing your knock sensor to a light 10 ft-lbs using a drop of thread locker rather than the 18 ft-lb spec to minimize sensitivity (the latter thought is debatable, but I did notice a slight improvement).

Hope that helps you with your problem and with keeping your 16-valve in top running shape.
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Dave -not to be confused with a real expert, just goofing around at this