My car is acting up, relatively stock 130k miles. It keeps setting ses light for MAP low voltage. I scanned it a couple times and noticed the map reading seemed ok. I forgot exact numbers but 101 w/ engine off and at WOT and like 50-60 at idle.

I replaced the map sensor and once again got the code.

I have had problems three times now, the ses light will come on, then the car won't rev w/ throttle input and it will eventually die.


I am thinking it is an electrical problem and maybe a loose wire because otherwise it works fine. The harness seems ok.

Any ideas?

 

What specific code did you get.... the one for low voltage/high vacuum, or the one for high voltage/low vacuum?

 

low voltage

 

To start, I would data log the car while driving and examine a trace of the MAP voltage signal. See what's its doing and then post back. The diagnostic is most likely an X out of Y counter. Basically, the DTC shows up when there is a MAP voltage below a calibrated value for X fails counts out of Y samples.

Post back with what you find.

 

The code sets when the sensor voltage drops below 0.24V on 45 out of 50 samples. The PCM uses every MAP reading as a "sample", and the rate is once every 6.25 milliseconds. But it only checks the MAP readings when the TPP is over 15%.

0.24V corresponds to less than 10kPA (a vacuum over 26"Hg). The normal minimum voltage the sensor is capable of producing is 0.30V. That would point to a short to ground. Obviously there is no way to see 26"Hg with the throttle at 15%, even on coast-down.

The MAP sensor harness connectors seem to crumble with old age, allowing shorts and intremittent readings. Have you checked the connector for damage? Did you try hooking up a volt meter, and jiggling the connector to see if the voltage fluctuates?