No Idle when cold 2000 GT
- Thread starter EnkeiWheels
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trinity_gt
10 Year Member
wmburns
SN Certified Technician
How to troubleshoot IAC Idle problems
+1 on above.
Have you adjusted the throttle body idle set screw in an attempt to resolve this (don't)?
For a slow idle check for vacuum leak between the air tube and the IAC.
There are a TON of posts regarding idle problems. Search?
Finally. Check out post 3
http://www.stangnet.com/mustang-forums/810729-starts-but-dies-idle-help.html
+1 on above.
Have you adjusted the throttle body idle set screw in an attempt to resolve this (don't)?
For a slow idle check for vacuum leak between the air tube and the IAC.
There are a TON of posts regarding idle problems. Search?
Finally. Check out post 3
http://www.stangnet.com/mustang-forums/810729-starts-but-dies-idle-help.html
trinity_gt
10 Year Member
You may also want to look at the EGR valve. If it's sticking, even a bit, it basically mimics a vacuum leak in terms of engine idling performance.
I did the test for the IAC (unplug the electrical connector) and it did as it was supposed to. Does that mean my IAC is good ?
I bought a contact cleaner to clean the MAF but i was surprised to see that there were security torx to remove it.. i'll buy some tomorrow.
How can i do a leak test ?
Thanks.
I bought a contact cleaner to clean the MAF but i was surprised to see that there were security torx to remove it.. i'll buy some tomorrow.
How can i do a leak test ?
Thanks.
wmburns
SN Certified Technician
The 1st IAC test is a basic functional test of the IAC stepper motor. Electrically, the IAC may be OK. But that does not positively prove the IAC is good.
Would you like an educated guess? Does the car run fine otherwise?
If so, the problem is likely in the IAC. Recall that the unit with the black vent has internal springs and valves. The valves are driven by a pressure differential that allows the vent to open during starting. What I think is happening is the vent is opening to allow the motor to start (as designed).
But it is NOT closing fully once the motor catches. This causes air to be drawn in through the vent. When the PCM switches to "closed loop", the PCM begins to use the MAF signal.
But the airflow as reported by the MAF is too low (flow split between MAF and IAC vent). This causes the PCM to compute an injector pulse width that is too short. The motor dies from lack of fuel.
It works better when the motor is warm because a warm motor does not depend as much on the fuel enrichment tables as does a cold motor. Further, perhaps the IAC is only leaking air or the vacuum of the running motor pulls it closed.
If this is the original IAC, this adds double to the chances of it being a bad IAC. The PCV vapors will gum up the inside thus making it stick.
If you don't like switching parts until you know for sure, by all means continue testing. In fact, because of the importance of the MAF, IMO almost every tech solution should start off with "clean MAF" as step #1.
This problem could also be a bad IAT. If the PCM doesn't know the correct input air temperature, this could also make the fuel enrichment tables wrong. Cross check the IAT with the current weather conditions. Is it reasonable? Use an ODB2 scanner to monitor. While you are at it, check the engine coolant temperature to see if it is reasonable. Especially after a cold soak.
Would you like an educated guess? Does the car run fine otherwise?
If so, the problem is likely in the IAC. Recall that the unit with the black vent has internal springs and valves. The valves are driven by a pressure differential that allows the vent to open during starting. What I think is happening is the vent is opening to allow the motor to start (as designed).
But it is NOT closing fully once the motor catches. This causes air to be drawn in through the vent. When the PCM switches to "closed loop", the PCM begins to use the MAF signal.
But the airflow as reported by the MAF is too low (flow split between MAF and IAC vent). This causes the PCM to compute an injector pulse width that is too short. The motor dies from lack of fuel.
It works better when the motor is warm because a warm motor does not depend as much on the fuel enrichment tables as does a cold motor. Further, perhaps the IAC is only leaking air or the vacuum of the running motor pulls it closed.
If this is the original IAC, this adds double to the chances of it being a bad IAC. The PCV vapors will gum up the inside thus making it stick.
If you don't like switching parts until you know for sure, by all means continue testing. In fact, because of the importance of the MAF, IMO almost every tech solution should start off with "clean MAF" as step #1.
This problem could also be a bad IAT. If the PCM doesn't know the correct input air temperature, this could also make the fuel enrichment tables wrong. Cross check the IAT with the current weather conditions. Is it reasonable? Use an ODB2 scanner to monitor. While you are at it, check the engine coolant temperature to see if it is reasonable. Especially after a cold soak.
