Symptoms
A bad Engine Control Unit (ECU) can cause any one or more of the following symptoms.
Intermittent 'clicking' behind the radio
If rapid clicking can be heard at times from the Multi-Port Injection (MPI) relay behind the radio while driving, a replacement ECU is needed. This is very common when the electrical circuitry inside the ECU has deteriorated from leaking capacitors.
Unable to start / Random stalling and only restarting after several tries, or when the car has cooled
If the vehicle only starts sometimes and not other times, a replacement ECU may be necessary. This is also true if the vehicle only starts when cold but suddenly stalls without restarting after warmed up. This condition will become more frequent until the vehicle cannot be started at all. A properly functioning ECU will illuminate the Check Engine Light (CEL) for a few seconds when the car is first cranked/started—if the CEL does not illuminate; the ECU is not powering up and will need to be replaced.
Running poorly with a severe decrease in power
If cylinders 1&4 or 2&3 are not firing and the coil packs are working properly, a replacement ECU is needed. If any sensor values are scanned and observed to be unreasonable (barometric, intake temperature, coolant temperature, etc), a replacement ECU may be needed. Depending on what parts of the ECU have been damaged, the vehicle may run poorly with significant decreases in fuel economy.
Low, unsteady or oscillating idle
If the vehicle has problems maintaining a consistent and steady idle speed (750 rpm when sufficiently warmed up) or has a rapidly fluctuating/oscillating idle (rapidly changing from 700 to 1500 rpm), a replacement ECU is needed. We also recommend testing and replacing the Idle Air Control (IAC) sensor if necessary.
Check Engine Light always on
If the check engine light is constantly illuminated and all the related sensors have been tested/replaced, a damaged ECU may be the culprit. Typical error codes include:
- Error Code 12 - Volume Air Flow Sensor
- Error Code 13 - Intake Air Temperature Sensor
- Error Code 25 - Barometric Pressure Sensor