High idle F225.....stumped

[panasonic]

I would think the 4.9 volts, key on, engine off is the 5 volt reference supplied to the sensor. Once engine starts then voltage on return wire to ECU should drop to corresponding pressure the sensor is seeing.

If you see no change in voltage after starting then that points to bad sensor. BUT you swapped sensor for a known good one with same results. So that would point to a wiring/plug problem from ECU to sensor?

Was continuity checked on the wires between sensor plug and ECU plug??

[99yam40]

I would think the 4.9 volts, key on, engine off is the 5 volt reference supplied to the sensor. Once engine starts then voltage on return wire to ECU should drop to corresponding pressure the sensor is seeing.

If you see no change in voltage after starting then that points to bad sensor. BUT you swapped sensor for a known good one with same results. So that would point to a wiring/plug problem from ECU to sensor?

Was continuity checked on the wires between sensor plug and ECU plug??

from what I have read, the map should read atmospheric pressure at key on to let the ECU know what altitude the motor is at before the motor starts.
that lets it know how much O2 is available to burn with the fuel

[panasonic]

from what I have read, the map should read atmospheric pressure at key on to let the ECU know what altitude the motor is at before the motor starts.
that lets it know how much O2 is available to burn with the fuel

Yes sir, you are correct, and I didn't explain what I was thinking very well in the first paragraph I wrote.

[mbureau22]

It's fixed!!!

looking back at what I did in the off season......it came about after routine maintenance and I had to move the MAP sensor/ISC valve out of the way to access the T-stat
Turns out there was a kink in the vacuum tube that I could not see until I removed the "body assay" that the ISC inserts into-
all this pain and testing from a kink in a vacuum line
Figured I would post the outcome incase someone has this issue in the future
really appreciate all the help form this forum!!!

[99yam40]

Maybe I am missing something,

I still do not understand how the map sensor would have 4.9 VDC on the output wire to the ECU even with the vacuum line pinched.

but thanks for posting up what you found, and that it is fixed now

[99yam40]

Just looked up the lowest ever recorded and it was 32 in.
which correlates to 2000 ft below sea leave.

my thoughts are the sensor is pegged out at 35.
so you need to find out why you have that 4.9 volts on the output of that Map sensor.
disconnect the sensor and measure that wire again to see what the wire has on it

OK it just hit me 35 is inches of mercury so that is lower than PSI

still need to find out where that voltage is getting into that wire from

it cannot be getting it from the sensor

Not sure how I came up with the 35 Inches of mercury thought
30 " is what we use to see when pulling a vacuum on vehicle's AC systems
too much to drink I guess