I have code 16 on the ECU so I am suspecting fuel injection problem but how to narrow this down. The CEL is not on however. Since the problem only happens after the car is hot (running maybe 20 minutes) I thought it is electrical related. Could a faulty relay cause this sort of problem? The car is difficult to start after it stalls when this problem is occurring, need to let it sit a few minutes.

If the CEL comes on for 2 seconds and then goes out, when the ignition switch is turned to ON (Position II), then I would replace the Ignition Control Module (ICM) and coil inside the distributor. Be sure to apply silicone heat transfer grease to the back of the new ICM. A failing ICM and coil are likely the main problem. The Code 16 will likely go away, once the ICM and coil are replaced. It's coincidental and there to confuse you and keep you from solving the real problem.

Examine the distributor cap and rotor carefully. Problems, here, can cause high secondary voltage to destroy the ICM and coil. Replace them, if they have not been changed in 50,000 miles.