Re: running on one
Good morning.
That is the IAP (inlet air pressure sensor). As you've substituted it, let's assume the unit itself is ok. To test it's supply disconnect the plug, & measure the voltage between the red wire & earth, you should have 4.5-5.5 volts. Then test between the red wire & the B/Br wire, which is the centre one in the plug. You should again see the above voltage.
If you don't have the above voltage present, you may have a poor connection on the ECU, or a break/iffy contact in the wiring harness.
As to why it runs with the vacuum pipe disconnected, it may be because the pipe is kinked or blocked, & the sensor can't read anything. So check the pipe to make sure it's clear of obstructions, & correctly connected at both ends.
Cheers.
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