Q: Stalling, misfiring, and erratic idle - 1995 Chevrolet K1500

asked by on November 12, 2016

After warm up, erratic idle rough running, stalling. Replaced iac, and tps.

My car has 189000 miles.
My car has a manual transmission.

Stalling and rough idling are usually an indication that the motor is not able to adjust to varying loads. The Manifold Absolute Pressure (MAP) sensor senses engine load and generates a signal that is proportional to the amount of vacuum in the intake manifold. The engine computer then uses this information to adjust ignition timing and fuel enrichment. When the engine is working hard, intake vacuum drops as the throttle opens wide. The engine takes in more air, which requires more fuel to keep the air/fuel ratio in balance.

When the computer reads a heavy load signal from the MAP sensor, it adjusts the fuel mixture to slightly more rich than normal so the engine can produce more power. The computer will then retard (back off) ignition timing slightly to prevent detonation (spark knock) that can damage the engine and decrease performance. This may also be caused by other closely related components, such as a dirty or failing mass airflow sensor, a faulty throttle position sensor, or potentially a vacuum leak.

I would recommend having an expert mechanic, such as one from YourMechanic, come to your location to determine why the car is stalling and determine if you need to replace your MAP sensor.

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