Engine Hanging Idle After Hard Acceleration

JustMan

Member
May 5, 2017
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I've been having some Idle issues with my 2004 mustang gt. After a hard acceleration The idle Hangs around 2k rpm and will hang there till I come to a complete stop and the car just dies. I've tried checking for vac leaks but cant seem to find any. I changed out the iac a couple of months ago. The codes I've got are P1000, P0442, P0405, And P0456. Anyone have any idea what it could be? I've linked a video of the idle and a picture of the codes I got.


View: https://youtu.be/lxk_vQuBGsg


imageedit_2_4923912718.jpg
 
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Have you recently disconnected the battery? If so that could explain the P1000. If the battery hasn't been disconnected recently, some thought should be given to a charging system "issue". The sudden quitting is also a possible sign of the weak battery or loose cable.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

IMO the P0405 is your worst problem. Anytime the PCM calls out a Circuit malfunction or "circuit low voltage" it means there's a major fault in the circuit. Think:
  • Failed sensor
  • dirty connectors pins
  • wiring fault
If this were my car I would start with a through visual inspection of the DPFE sensor connector and wiring.

But If $$ isn't really an issue for you, I would start by replacing the DPFE sensor. The failure rate is high enough to justify replacing for pure diagnostic reasons. There have been updates the the calibration used inside the DPFE sensor. Consider a name brand Ford product. Also make sure that the vacuum lines to/from the DPFE sensor are in good shape. The hot exhaust gas is very hard on the rubber.

The high idle could also be caused by a leaking canister purge value or vapor management valve. Trouble shooting EVAP problems can be a real challenge. Having an ODB2 scanner with two way activation can make short work of the problem.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

P0405 - DPF EGR Sensor Circuit Low Voltage Detected
See DTC P1400

P1400 - DPF EGR Sensor Circuit Low Voltage Detected
  • DPFEGR circuit short to GND
  • Damaged DPF EGR sensor
  • VREF short to GND
  • Damaged PCM
P0456 - EVAP Control System Leak Detected (Very Small Leak)

P0442 - EVAP Control System Leak Detected (Small Leak)
 
Last edited:
Have you recently disconnected the battery? If so that could explain the P1000. If the battery hasn't been disconnected recently, some thought should be given to a charging system "issue". The sudden quitting is also a possible sign of the weak battery or loose cable.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

IMO the P0405 is your worst problem. Anytime the PCM calls out a Circuit malfunction or "circuit low voltage" it means there's a major fault in the circuit. Think:
  • Failed sensor
  • dirty connectors pins
  • wiring fault
If this were my car I would start with a through visual inspection of the DPFE sensor connector and wiring.

But If $$ isn't really an issue for you, I would start by replacing the DPFE sensor. The failure rate is high enough to justify replacing for pure diagnostic reasons. There have been updates the the calibration used inside the DPFE sensor. Consider a name brand Ford product. Also make sure that the vacuum lines to/from the DPFE sensor are in good shape. The hot exhaust gas is very hard on the rubber.

The high idle could also be caused by a leaking canister purge value or vapor management valve. Trouble shooting EVAP problems can be a real challenge. Having an ODB2 scanner with two way activation can make short work of the problem.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

P0405 - DPF EGR Sensor Circuit Low Voltage Detected
See DTC P1400

P1400 - DPF EGR Sensor Circuit Low Voltage Detected
  • DPFEGR circuit short to GND
  • Damaged DPF EGR sensor
  • VREF short to GND
  • Damaged PCM
P0456 - EVAP Control System Leak Detected (Very Small Leak)

P0442 - EVAP Control System Leak Detected (Small Leak)
I have not disconnected the battery recently I'll try a charging system voltage drop test tomorrow. The guy I bought the car from did an egr delete so the egr and the dpfe are gone. I did get a tune recently and mentioned to them that the car had an egr delete I'm not sure if they still took it into consideration because the egr codes are still showing up.
 
I have not disconnected the battery recently I'll try a charging system voltage drop test tomorrow. The guy I bought the car from did an egr delete so the egr and the dpfe are gone. I did get a tune recently and mentioned to them that the car had an egr delete I'm not sure if they still took it into consideration because the egr codes are still showing up.
Well. Given the DTC codes IMO it's a sure bet that the EGR delete was not fully done and the PCM is still attempting to run the EGR monitors. Likely the fact that the EGR monitors are not able to complete also explains the never ending P1000.