Can you set the desired idle RPM differently for only when the AC is on or does it have to be across the board and then it adjusts because of the load the compressor puts on the motor?
idle rpm w/ ac on?
- Thread starter DSG2003Mach1
- Start date
Im not a tuner @DSG2003Mach1 But i believe the answer to your question is NO.The most common cause of rough idling while the AC is on, is usually caused by a dirty throttle body. A brief initial loss of rpm as the AC comes on is normal. When the AC clutch engages to run the compressor, it places an additional load on the engine. But the car's computer (PCM) should bring the idle speed back up. Maybe @decipha can clarify on this question.
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That’s kinda my thought, it’s really more about alternator output but trying to avoid going down that rabbit hole of info that doesn’t change the outcome of my question if ya know what I mean
Yea I know what you mean. The PCM dictates the output of the alternator as well.
Hmmm, also true, is there a way to see commanded? Never thought about that. My assumption is it just can’t keep with the load at such low rpm but I suppose crazier things have happened
*The alternator F terminal is a duty cycle signal that reflects field operation. The PCM monitors the F terminal to determine the alternator's load on the engine. The PCM uses this information to adjust engine RPM and alternator voltage set point.
Depends on how much load is being put on the charging system. So a simple test. Start by adding load on the charging system and observe a clamp on ampmeter on the alternator. Positive increments in amps indicate proper load requirements are being commanded by the PCM.
Procedure: To check alternator and load demand
After connecting an ammeter correctly in the battery circuit, continue as follows:
1. Start the engine and operate to about 2,000 RPM (fast idle).
2. Turn the heat selector to air-conditioning (if the vehicle is so equipped).
3. Turn the blower motor to high speed.
4. Turn the headlights on bright.
5. Turn on the rear defogger.
6. Turn on the windshield wipers.
7. Turn on any other accessories that may be used continuously (do not operate the horn, power door locks, or other units that are not used for more than a few seconds).
Observe the ammeter. The current indicated is the electrical load that the alternator is able to exceed to keep the battery fully charged.
Test Results
The minimum acceptable alternator output is 5 amperes greater than the accessory load. A negative (discharge) reading indicates that the alternator is not capable of supplying the current (amperes) that may be needed.
always coming in clutch vinnie. Appreciate your knowledge man.
Pcm desires a certain rpm. It drives the IAC to achieve that.
As mentioned above, do an idle relearn.
Sent from my iPhone using svtperformance.com
As mentioned above, do an idle relearn.
Sent from my iPhone using svtperformance.com
In Binary Editor I can add RPM to my idle when the compressor is on. EEC-V. The stock RPM added is *I think* 68 RPM…I’ll have to look tomorrow to verify.
yep, DNAC are the pid's that add rpm for the a/c there is also a PPM adder to kick up the iac.
The mustang didn't get alternator control from the pcm til 2005.
The mustang didn't get alternator control from the pcm til 2005.
Thanks guys
I have a clamp meter being delivered today to try and figure out wtf is going on
Sorry for the wrong info on the PCM/ Alternator control @DSG2003Mach1 . I new this happened in the mid 2000's but it didnt cross my mind to ask you what vehicle we were dealing with for this specific issue. Now that im aware this is for your 2003 Mach 1 and not your 2012 F150. Again I apoligize. If you need any help narrow this issue down dont hestitate to ask. Im assuming your rpm drop is happening when the AC is turned on and its not coming back up to a correct or high enough rpm due to the load if thats the correct issue at hand. Let me know.
@decipha & @2003RedfireVert
1) when logging should I be able to find a pid in livelink2 for that? I didnt see it. I saw idle speed adder for ac and it was always 0.0
2) the RPM kick up with AC on - Desired Idle RPM is 850, it bounces all around the 800 range for high and low but the average is right at 850. If the kick up for the AC is suppoed to be 65 rpm - does that mean desired idle is now 915 or is it still 850 but without the kickup it would idle @ 785?
1) when logging should I be able to find a pid in livelink2 for that? I didnt see it. I saw idle speed adder for ac and it was always 0.0
2) the RPM kick up with AC on - Desired Idle RPM is 850, it bounces all around the 800 range for high and low but the average is right at 850. If the kick up for the AC is suppoed to be 65 rpm - does that mean desired idle is now 915 or is it still 850 but without the kickup it would idle @ 785?
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it kicks it up 65
log desired rpm
log desired rpm
It doesn’t change, desired idle rpm is always 848, never changes
Actual idle maintains the same rpm range and average as ac off
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I think that this might help you with your AC RPM issue @DSG2003Mach1
*Give it a try
Idle Air Trim
Idle Air Trim is designed to adjust the Idle Air Control (IAC) calibration to correct for wear and aging of components. When engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The Idle Air Trim values are stored in a table for reference. This table is used by the PCM as a correction factor when controlling idle speed. The table is stored in keep alive memory (KAM) and retains the learned values even after the engine is shut off. A Diagnostic Trouble Code (DTC) is output if the Idle Air Trim has reached its learning limits.
Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that keep alive memory be cleared. This is necessary so the idle strategy does not use the previously learned Idle Air Trim values.
To clear the keep alive memory.Resetting the KAM returns the PCM memory to its default setting. Adaptive learning contents such as idle speed, refueling event, and fuel trim are included. To clear the continuous DTCs in the PCM and have it reset the emissions monitors information, is also part of a KAM reset.
After the KAM has been reset, the vehicle may exhibit certain driveability concerns. It is necessary to drive the vehicle to allow the PCM to learn the values for optimum driveability and performance.
Once keep alive memory has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as the strategy adapts. Adaptation occurs in four separate modes. The modes are shown in the following table.
IDLE AIR TRIM LEARNING MODES
*Give it a try
Idle Air Trim
Idle Air Trim is designed to adjust the Idle Air Control (IAC) calibration to correct for wear and aging of components. When engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The Idle Air Trim values are stored in a table for reference. This table is used by the PCM as a correction factor when controlling idle speed. The table is stored in keep alive memory (KAM) and retains the learned values even after the engine is shut off. A Diagnostic Trouble Code (DTC) is output if the Idle Air Trim has reached its learning limits.
Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that keep alive memory be cleared. This is necessary so the idle strategy does not use the previously learned Idle Air Trim values.
To clear the keep alive memory.Resetting the KAM returns the PCM memory to its default setting. Adaptive learning contents such as idle speed, refueling event, and fuel trim are included. To clear the continuous DTCs in the PCM and have it reset the emissions monitors information, is also part of a KAM reset.
After the KAM has been reset, the vehicle may exhibit certain driveability concerns. It is necessary to drive the vehicle to allow the PCM to learn the values for optimum driveability and performance.
Once keep alive memory has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as the strategy adapts. Adaptation occurs in four separate modes. The modes are shown in the following table.
IDLE AIR TRIM LEARNING MODES
Transmission Range | Air Conditioning Mode |
|---|---|
| NEUTRAL | A/C ON |
| NEUTRAL | A/C OFF |
| DRIVE | A/C ON |
| DRIVE | A/C OFF |
This could possible be the issue as well.
Air Conditioning Pressure Sensor
The air conditioning pressure (A/C pressure) sensor (Figure 24)is located in the high pressure (discharge) side of the air conditioning A/C system. The A/C pressure sensor provides a voltage signal to the powertrain control module (PCM) that is proportional to the A/C pressure. The PCM uses this information for A/C clutch control, fan control and idle speed control.
Air Conditioning Pressure Sensor
The air conditioning pressure (A/C pressure) sensor (Figure 24)is located in the high pressure (discharge) side of the air conditioning A/C system. The A/C pressure sensor provides a voltage signal to the powertrain control module (PCM) that is proportional to the A/C pressure. The PCM uses this information for A/C clutch control, fan control and idle speed control.
thanks @Vinnie_B
I did not think to verify that the pcm is recognizing the ac compressor being on- I believe there’s a flag for that. I’ll double check that tomorrow.
At this point by the fact that commanded idle rpm doesn’t change I’m leaning towards tuner made a boo-boo and removed the rpm kick up. As of now it appears the actual and desired rpm match… but desired isn’t changing
I did not think to verify that the pcm is recognizing the ac compressor being on- I believe there’s a flag for that. I’ll double check that tomorrow.
At this point by the fact that commanded idle rpm doesn’t change I’m leaning towards tuner made a boo-boo and removed the rpm kick up. As of now it appears the actual and desired rpm match… but desired isn’t changing
Air Conditioning Cycling Switch
The air conditioning (A/C) cycling switch may be wired to either the ACCS or ACPSW PCM input. When the A/C cycling switch opens, the PCM will turn off the A/C clutch.
The A/C cycling switch (ACCS) circuit to the PCM provides a voltage signal which indicates when the A/C is requested. When the A/C demand switch is turned on, and both the A/C cycling switch and the high pressure contacts of the A/C high pressure switch (if equipped and in circuit) are closed, voltage is supplied to the ACCS circuit at the PCM.
If the ACCS signal is not received by the PCM, the PCM circuit will not allow the A/C to operate.
*Check your ACCS PID as well
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