Missing and rough idle
Stellar HDF Member
Joined: Sep 2007
Posts: 2,434
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From: Vancouver Island B.C.
Even after replacing the cap it can still stumble as the ecm has to relearn the proper amount of steps.
Seasoned HDF Member
Joined: Aug 2006
Posts: 24,423
Likes: 30,643
From: Pennsylvania
P0505 Idle speed control unstable
https://www.fuelmotousa.com/p-29661-...ble-codes.html
Last edited by CoolBreeze3646; Dec 21, 2025 at 07:29 PM.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
The ECM shouldn't need to relearn a sensor. It either receives the signal from the sensor, or it doesn't....
I believe the MAP sensor for your year is also a T-Map sensor which gives both intake air pressure and intake air temp signals to the ECM.
If I am correct, since after replacing the T-MAP sensor with a new one (a presumably good sensor) and now you have two T-Map sensor codes, I would suggest one of two things has happened.
1) You have been given a bad T-Map sensor out of the box. Rare, but it does happen.
2) More likely, there is either an issue with the t-Map connector, or the wires between the sensor and the ECM, inhibiting proper communication between the two.
Based on two codes from one sensor, I would first primarily focus on that T-Map sensor and it's ability to communicate with the ECM.
I'd start by checking the connection at the T-Map sensor. Make sure there is no damage/corrosion to the internal connector pins, or the wires at the connector (ie broken under the insulation).
If they check out, then get the Electrical diagnostic manual to see what type of signal is being sent between the sensor and the ECM. I'm not particularly well versed in electrical issues, so without consulting the manual, I can't tell you how the ECM and T-Map sensor communicate to each other.
Once you know what to look for, then check the appropriate connector for the proper signal(s).
If no signals are found, then you have to check the appropriate part (sensor or ECM) to make sure it's sending the proper signal.
If no signal is being sent from the part supposed to initiate comms between the two, you have located the bad part. If signal is sent, but not received, you have bad wires/connectors.
I hope this makes sense, but off the top of my head I really don't know how the ECM & T-Map sensor communicate with each other, or what signals are being sent... so I can't be more specific...
If I have errored in my thinking, someone will surely point it out...
I hope some of this info helps...
I believe the MAP sensor for your year is also a T-Map sensor which gives both intake air pressure and intake air temp signals to the ECM.
If I am correct, since after replacing the T-MAP sensor with a new one (a presumably good sensor) and now you have two T-Map sensor codes, I would suggest one of two things has happened.
1) You have been given a bad T-Map sensor out of the box. Rare, but it does happen.
2) More likely, there is either an issue with the t-Map connector, or the wires between the sensor and the ECM, inhibiting proper communication between the two.
Based on two codes from one sensor, I would first primarily focus on that T-Map sensor and it's ability to communicate with the ECM.
I'd start by checking the connection at the T-Map sensor. Make sure there is no damage/corrosion to the internal connector pins, or the wires at the connector (ie broken under the insulation).
If they check out, then get the Electrical diagnostic manual to see what type of signal is being sent between the sensor and the ECM. I'm not particularly well versed in electrical issues, so without consulting the manual, I can't tell you how the ECM and T-Map sensor communicate to each other.
Once you know what to look for, then check the appropriate connector for the proper signal(s).
If no signals are found, then you have to check the appropriate part (sensor or ECM) to make sure it's sending the proper signal.
If no signal is being sent from the part supposed to initiate comms between the two, you have located the bad part. If signal is sent, but not received, you have bad wires/connectors.
I hope this makes sense, but off the top of my head I really don't know how the ECM & T-Map sensor communicate with each other, or what signals are being sent... so I can't be more specific...
If I have errored in my thinking, someone will surely point it out...
I hope some of this info helps...
I'd go with #2 tho I wouldn't say it's a communication issue. These are dumb sensors in the same location.. The map is solid state device with the output from roughly 0.5V to 0.45 volts and the IAT sensor is nothing more than a thermistor (temperature variable resistor). Since both are reading high, I'd suspect a bad ground to tmap. Tug on the ground wire, reseat the connector in the ECM that has that wire.
Seasoned HDF Member
Joined: Dec 2005
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From: poway
Do servo controlled throttle bodies still use the IAC parameter to emulate the IAC since it doesn't have one?
Stellar HDF Member
Joined: Sep 2007
Posts: 2,434
Likes: 658
From: Vancouver Island B.C.
show a tps of 7-8%. When fully warm you may see as low as 3%.
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