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When MAP Sensors on Older Cars Fail - Idle Hesitation, Sluggish Acceleration

Mechanic Under Car

Older vehicles from the mid-1980s through the 1990s were often fitted with manifold absolute pressure (MAP) sensors, a precursor to mass air flow (MAF) sensors. These were introduced in the early and mid 1980s as a way to measure airflow through the intake more precisely.

MAP sensors are relatively simple, measuring airflow in real-time and feeding that information to the engine control unit (ECU), which used it to make continual fuel flow adjustments to optimize burn rates in the engine. When the MAP sensor malfunctions or stops functioning altogether, the ECU often sends too little or too much fuel, which can cause rough or hesitant idle and sluggish acceleration.

MAP sensors are still in use today, usually on turbocharged engines to measure the air flow rate into the throttle body in concert with a MAF sensor, giving the ECU precise measurements of air movement through the intake.

MAP sensors are also often used to test exhaust gas recirculation systems. In more modern engines, it's relatively rare for the fairly simple MAP sensor to become inoperable. In older engines, however, these primitive sensors were often prone to circuit problems, clogging, and so forth.

On an older engine with idle and acceleration problems, it's good to pull engine codes to see if the MAP sensor is coming up. It's also a good idea to test the MAP sensor's circuit for functionality and, of possible, to swap the MAP sensor with one known to be functioning to see if things improve.