03 4.6 SN95 Idle issues

Hostilevibes · Jul 10, 2018

I have an 03 mustang Gt with constant idle issues. In park the car acts like it’s misfiring intermittently. In gear and at a stop the idle will go from 680 RPM’s and gradually lose RPM’s until it reaches the low 475 to 500 RPM’s. While this fall out happens the car vibrates extremely badly and has a hesitation when accelerating. I have no DTC’s except for a P0455 and the car is completely stock except for a K&N CAI and BBK O/R X Pipe. I have replaced the TPS, MAF, Coolant Sensor, all spark plugs and COP’s, alternator, idler pulley, belt tensioner, Torque Converter, Fuel Filter, Fuel Rail Pressure Sensor, Fuel Pump Driver Module, Idle Air Control, EGR, Crank Sensor and Cam Sensor, upstream O2 Sensors, and MIL Eliminators for the rear O2 sensors. Also, sometimes when I go from Drive to Park the car will idle to around 1500 RPM’s and hang. If anyone can help me please do. Attached below is a picture of one of the scanners TID $01 CID $11 data, does anyone know what this means?

wmburns · Jul 10, 2018

Did you swap all of those parts in an attempt to fix the idle problem?

Which IAC valve does your car use? (black vented or non-vented)? What happens when the IAC electrical connector is disconnected while the motor is running at idle?

Does your ODB2 scanner have the TP-MODE PID? Or TPS voltage? Or IAC duty percentage?

Does the car's speedometer work?

What is the voltage at the battery when the idle is poor? When the idle is good?

Does the ODB2 mode 6 misfire data (TID $51) actually show there are misfires? We can't expect the motor to run well with active misfires.

What steps have you taken to "adjust" the throttle body idle stop screw?

What have you done to rule out a vacuum leak? Is the FRPS intake vacuum reference line connected and leak free?

Are you positive that the battery and charging system is in tip top shape? No excessive AC ripple?

TID $01 = oxygen sensors

Raw ODB2 mode 6 data is very difficult to de-code. Perhaps an updated scanner firmware from the maker's web site? Here's some information on an affordable Windows based full function ODB2 scanner with graphing capabilities.

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

Troubleshoot IAC idle problems 1996-2004
https://www.stangnet.com/mustang-forums/resources/troubleshoot-iac-idle-problems-1996-2004.13/

On the Troublehooting how to pay special attention to the role that the TPS plays in closed throttle determination. Don't focus on a specific value for the TPS. The KEY is the TPS voltage needs to be the SAME each time the throttle is closed.

Hostilevibes · Jul 15, 2018

Sorry I just got out of the hospital I’ll be pulling the car out of the garage and I’ll let you know what I find. I really appreciate you giving me some insight on where to start. And the only questions I can answer at the moment is most of the parts I listed were replacements because I bought the car off my friend and it didn’t run. I got it running but something still isn’t right. Especially hotter temps it’s like the motor is bogging itself down. I had a smoke test done on it when I originally suspected a vacuum leak to be the sole cause. My IAC is a Bosch ventless assembly but I didn’t play with the idle stop screw. Was i supposed to when I replaced the tps? Once I get to the garage I’ll run through the tests and give you the information I find.

03 4.6 SN95 Idle issues

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03 4.6 SN95 Idle issues

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