The ECM generally works or doesn't.
But signs you have one going are hard to diagnose. But some I have seen:
The problem with this list is that every symptom is more likely caused by an external source.
There are a number of signs that become apparent when an ECM computer on a 1990 Chevy is going bad. The top signs include a non-functioning speedometer and flashing codes on the dash.
Some of the top signs of a transmission issue would be that the car isn't switching gears or it is noisy when in neutral. Other signs would be that their is a bad smell.
A bad computer could cause several problems. The car may not shift properly. The overdrive might not work. In some models the transmission may stay in forward gears no matter what the selector is set to.
A bad ingnition module, Are a bad computer.
There are several signs that an alternator is going bad. A few signs are dim lights, smell, warning lights, and a dead battery.
some of the classic signs of a tranny going bad is leaking, slipping in and out of gear delayed starts from a stop where the car raises rpms before it takes off and shaking or jerking when its going into gear
it is probably a bad ignition module or computer
Ignition module, cam senor, crank sensor or bad computer
The engine control module can affect cylinders. But if its only a 4 cylinder, cancelling out just one out of 4 isn't likely to be a computer. Its not the most likely cause, but it is definetely possible.
If you're not using a heat sink grease between the module and the mount area try using some on your next replacement module.
You go to wiki.answers.com
less heat in your car