High idle F225.....stumped

[mbureau22]

I have twin 2005 F225s. Port engine has a high idle.....900 or so. This past off season I did T-stats. I have YDS a which shows code 29 (MAP sensor out of spec) and this is what I have done so far:

Port engine key on/engine off:
Intake press 35
atm press 30

Start the engine and there is no change in the intake press.....remains at 35
obviously it should never read 35 as that is higher the the atm pressure

I swapped the MAP sensors....no change
swapped the ISC valves......no change
swapped ECUs.....no change

Voltage to MAP sensor is 4.98V

Any ideas? Plan to make sure I didn't pinch a vacuum hose when I did stats but don't see how that would cause an elevated intake pressure.

Not that this should effect it but both midsections were done in 2021.

Engine runs perfect in gear and spins up to 6000 RPM. In gear the RPMs drop to the normal 600.

Thanks in advance.

[99yam40]

if you disconnect the Map sensor, does it still show 35?
very strange that swapping did not change anything
something to do with the wiring harness maybe

[boscoe99]

How about the voltage output from the MAP sensor?

Low pressure equals low voltage. High pressure equals high voltage. Talking about voltage seen by the ECU/EMM/PCM from the sensor.

[mbureau22]

The voltage to the MAP sensor was 4.98V. That was key on engine off.

[boscoe99]

I was talking about voltage from the sensor and not to the sensor.

[mbureau22]

How would I check the voltage from the sensor?

[boscoe99]

Voltmeter.

[99yam40]

same way you checked the voltage to the sensor, but on a different wire

[mbureau22]

I should have asked which wires to check....

[boscoe99]

Pink/green. As shown in your service manual wiring diagram.

[99yam40]

How about the voltage output from the MAP sensor?

Low pressure equals low voltage. High pressure equals high voltage. Talking about voltage seen by the ECU/EMM/PCM from the sensor.

Boscoe, what is the highest that sensor would read is there was a short to the 5 volt reference wire?

35?
or maybe a lot higher?

[mbureau22]

Pink/green wire at plug for MAP sensor also shows 4.9volts

[99yam40]

My only thought is what does the other motors Map sensor voltage read?

Hope Boscoe can answer my question on how high can it read.

if by chance that the wring harness has shorted or just a connector itself has
and 35 is the highest the system can read with that full 5 Volts.
that might explain why swapping those parts out did not change things

[boscoe99]

Pink/green wire at plug for MAP sensor also shows 4.9volts

What is the voltage on the sensor for the other motor?

In another service manual, for a different model, different part number pressure sensor, Yamaha shows two voltages, based on the pressure to the MAP sensor being lowered.

3.21 volts at 11.8 psi and 2.16 volts at 7.9 psi.

[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