Progress Thread 2003 Mach stalls

Hello all

I have a 2003 Mach 1 that stalls when AC is turned on when the car reaches its normal temperature. IAC, MAF & TB have been cleaned also checked for leaks and all clear. I have also changed the O2 sensors upstream. The Mach also stalls at times in stop/red lights AC off.

After the built the Mach would stall here and there while slowing down or complete stops obviously needing a tune. RPM’s at idle would be around 8-9 roughly, now just before the tune my brother swap the battery and connected it backwards for a good 2 seconds. Lighter and stereo fuse are the only fuses that blew but the Mach didn’t feel the same. At idle it would now be at 5-6, it would struggle more to stay on. I got the tune done but the stalling is still there I feel it stalls even more after the battery incident.


Modifications
Engine built .30 over
Camm work
MAF 90
42lbs injectors
CAI JLT
Off X pipe
Chipped and tuned[/QUOTE]
 
  • Sponsors (?)


What have you done to CONFIRM that the IAC is actually working? Have you verified that the IAC duty percentage is within limits? Does the motor's RPM's drop (or quit out right) if the IAC is disconnected?

What is the state of repair of the AC system. Does the AC short cycle?

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

Do you have access to an ODB2 scanner capable of monitoring operational data? If so, this might make short work of this problem.

Here's some information on an affordable Windows based unit.

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

Don't discount the role that a weak battery and charging system could play in a motor that quits for an unknown reason.

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

I have a 2003 Mach 1 that stalls when AC is turned on when the car reaches its normal temperature. IAC, MAF & TB have been cleaned also checked for leaks and all clear. I have also changed the O2 sensors upstream. The Mach also stalls at times in stop/red lights AC off.

After the built the Mach would stall here and there while slowing down or complete stops obviously needing a tune. RPM’s at idle would be around 8-9 roughly, now just before the tune my brother swap the battery and connected it backwards for a good 2 seconds. Lighter and stereo fuse are the only fuses that blew but the Mach didn’t feel the same. At idle it would now be at 5-6, it would struggle more to stay on. I got the tune done but the stalling is still there I feel it stalls even more after the battery incident.


Modifications
Engine built .30 over
Camm work
MAF 90
42lbs injectors
CAI JLT
Off X pipe
Chipped and tuned
[/QUOTE]

When I disconnect the IA
Hello all

I have a 2003 Mach 1 that stalls when AC is turned on when the car reaches its normal temperature. IAC, MAF & TB have been cleaned also checked for leaks and all clear. I have also changed the O2 sensors upstream. The Mach also stalls at times in stop/red lights AC off.

After the built the Mach would stall here and there while slowing down or complete stops obviously needing a tune. RPM’s at idle would be around 8-9 roughly, now just before the tune my brother swap the battery and connected it backwards for a good 2 seconds. Lighter and stereo fuse are the only fuses that blew but the Mach didn’t feel the same. At idle it would now be at 5-6, it would struggle more to stay on. I got the tune done but the stalling is still there I feel it stalls even more after the battery incident.


Modifications
Engine built .30 over
Camm work
MAF 90
42lbs injectors
CAI JLT
Off X pipe
Chipped and tuned
[/QUOTE]

The IAC when I disconnect it the car shuts off immediately. Right now it’s throwing a code P0141 O2 sensor heater circuit malfunction bank 1 sensor 2.
 
Seems to me that there's a real chance that the P0141 is not helping. With this outstanding DTC there's no way that the PCM is in closed loop mode.

Anytime the PCM calls out a circuit malfunction that means there's something sooooooooooo wrong with the circuit that the PCM is unable to perform any real trouble shooting.

If this were my car, I would first check fuse F2.2 and F2.8 to see if they are blown. Next I would check the wires to/from each of the O2 sensors to look for wiring harness damage. For example physical damage such as touching hot exhaust.

1999-2004 MY fuse panel schedule:
 
Seems to me that there's a real chance that the P0141 is not helping. With this outstanding DTC there's no way that the PCM is in closed loop mode.

Anytime the PCM calls out a circuit malfunction that means there's something sooooooooooo wrong with the circuit that the PCM is unable to perform any real trouble shooting.

If this were my car, I would first check fuse F2.2 and F2.8 to see if they are blown. Next I would check the wires to/from each of the O2 sensors to look for wiring harness damage. For example physical damage such as touching hot exhaust.

1999-2004 MY fuse panel schedule:

Ok I checked the fuses and yes F2.2 was blowned even when I checked it it was marking ok but I pulled it out and yes it was blowned.
 
Am I good or what?

Given the fact that fuse F2.2 powers to IAC is it a surprise there's a problem with the idle? Plus none of the other 12 volts sensors are working either.


Ok I replaced the fuse and am still having the same issues when the car is warmed up. Today I drove it to work about 20 mile drive and didn’t stall until I parked it died. Also when On using both power windows once there up or down I hold on and it stalls, AC on it stalls. The headlights too, the rpms up and down then it stalls.

When the tune was done I believe this fuse was blown already, could that be it?
 
Soooooooooooooooooooo. Did you check to see IF the fuse blew again?

Do you KNOW WHY the fuse blew in the first place? I don't know about your car but I have owned cars for years without ever replacing a fuse.

Again, if the IAC is not working because of a blown fuse is it a surprise that the idle is unstable? I'm including some information about how to trouble shoot IAC issues. Since your car does continue to run with a blown F2.2 fuse (non functioning IAC), the only reasonable explanation is someone has attempted to adjust the throttle body idle stop screw in an attempt to keep it running. The result will always be that the car will idle in the exact conditions that the stop was set but won't when the temperature changes are the motor load changes (think AC on/off or other loads). Note the part about what should happen when the IAC is disconnected (motor should die outright or run very slowly).

Troubleshoot IAC idle problems 1996-2004

Just wondering. Did you read the information in the "how to perform a voltage drop test"? How about the part where it says, "today's cars simply will not run right without a strong battery and charging system"? When a problem occurs when there's a large electrical step load change this screams there's a problem with the charging system. The system voltage is not stable for some reason. Do yourself a favor and find out WHY before doing anything else.

I personally would be very upset if someone attempted to tune a car that wasn't working well in the first place.
 
Last edited:
Soooooooooooooooooooo. Did you check to see IF the fuse blew again?

Do you KNOW WHY the fuse blew in the first place? I don't know about your car but I have owned cars for years without ever replacing a fuse.

Again, if the IAC is not working because of a blown fuse is it a surprise that the idle is unstable? I'm including some information about how to trouble shoot IAC issues. Since your car does continue to run with a blown F2.2 fuse (non functioning IAC), the only reasonable explanation is some has attempted to adjust the throttle body idle stop screw in an attempt to keep it running. The result will always be that the car will idle in the exact conditions that the stop was set but won't when the temperature changes are the motor load changes. Note the part about what should happen when the IAC is disconnected (motor should die outright or run very slowly).

Troubleshoot IAC idle problems 1996-2004

Just wondering. Did you read the information in the "how to perform a voltage drop test"? How about the part where it says, "today's cars simply will not run right without a strong battery and charging system"? When a problem occurs when there's a large electrical step load change this screams there's a problem with the charging system. The system voltage is not stable for some reason. Do yourself a favor and find out WHY before doing anything else.

I personally would be very upset if someone attempted to tune a car that wasn't working well in the first place.


Awesome knowledge, thank you I wouldn’t of known about the fuse since the tester was indicating good. My car sat for a bit and my brother crossed the battery cables for a good 2 seconds, it blew the regular fuses radio cigar lighter and the F2.2 that I didn’t know about with this said yes I messed with the screw a bit but before I did I marked it. I will put it back in place.
FYI when I would disconnect the IAC it would die ASAP but that test was done with the fuse blown. I will try it again.

Yes it’s upsetting I seen other tuner’s on you tube they won’t do ANYTHING until the car is running correctly. Lack of knowledge my end.

I will read it again on the voltage drop test, mind you before the cables were crossed the Mach wouldn’t do what it does now.
 
Awesome knowledge, thank you I wouldn’t of known about the fuse since the tester was indicating good. My car sat for a bit and my brother crossed the battery cables for a good 2 seconds, it blew the regular fuses radio cigar lighter and the F2.2 that I didn’t know about with this said yes I messed with the screw a bit but before I did I marked it. I will put it back in place.
FYI when I would disconnect the IAC it would die ASAP but that test was done with the fuse blown. I will try it again.

Yes it’s upsetting I seen other tuner’s on you tube they won’t do ANYTHING until the car is running correctly. Lack of knowledge my end.

I will read it again on the voltage drop test, mind you before the cables were crossed the Mach wouldn’t do what it does now.

Sorry for the late update, so after checking everything and replacing the fuses the were blown I had no other choice but to take it to another tuner. I explained the problems and right away he pin pointed the issues which had to do with the tune. He returned the Mach and no more stalling.