2001 mustang GT idling

i have a 2001 mustang GT. whenever i drive and stop abruptly the rpms will dip below the normal level and it will stay there for a couple seconds shaking before it goes back to the normal idle. ive already replaced the idle air control valve and that didnt fix it. can someone please tell me what is going on before i pull all my hair out?!?
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Check for codes? May be there in the absence of a CEL.
As described, it sounds like it’s an automatic.true, or a 5 speed?
Drive it with the A/C on, does the idle stabilize normally?
Eliminating basics, check for spark delivery issues that may drop a cylinder at low RPM’s, clean cap posts, plugs & regal, check wires for resistance, use a little dielectric grease on on plug contacts & never seize on the threads.
Check all your vacuum lines for cracks & otherwise bad connections, repair. Test parts. prior to replacing them. Very helpful link below:

Good luck!
hello john and thank you for responding. there is no check engine light its an automatic and i cant find a vacuum leak. i just replaced the spark plugs. i did notice its random. when the car sits in the driveway idling it idles fine. and if i come to a gentle stop it idles fine. sometimes whenever i stop abruptly it does it. its kind of strange.
No luck with the checklist?
Did you check for codes? Have a code reader? Autozone will pull codes for free.
That should shed more light on the issue.
Few things you can do in the meantime is
Try checking your charging system with a VOM, e.g. the battery & it’s voltage, and is held tightly in place.
Check Alternator output & the conditions of the charging system, clean it’s terminals & associated wiring.(13.5-13.8 DCV, running).
A weak battery (< 12.5 Volts) or an insufficient charging system output or poor connections may cause issues such as this.
It’s common if you’ve accumulated media, e.g. rust, etc. in the fuel tank, it will Slosh forward under hard stops and temporarily starve the car of fuel by blocking the line in these scenario’s. Pulling your fuel filter should yield evidence of this. It’s not just pressure, it’s flow rates that also need be sufficient.
Other than pulling the tank, someone rocking the car side to side with your ear up to it will allow you to hear if significant residue exists inside the bottom of the tank, as that’s where it settles.
Car had a thorough tune up lately? Check the connections on your Cool air intake & filter, clean your MAF sensor with CRC MAF sensor cleaner.
Don’t forget to try to pull codes.
Good luck
hello and thank you for responding. i recently checked it out and found out it idled bad because the throttle was set too low on the throttle body. it idled at 500 rpm. i raised it to 750 and now my issue is fixed. thanks for the advice though :nice:
hello and thank you for responding. i recently checked it out and found out it idled bad because the throttle was set too low on the throttle body. it idled at 500 rpm. i raised it to 750 and now my issue is fixed. thanks for the advice though :nice:
No problem! If you run into other problems, just wanted you to know this. Is the throttle body stock, and is the Cam stock?
This idle getting lower just occurred out of the blue-correct, If true, that indicates another issue caused the low idle.
As a general rule of thumb, when a low idle condition occurs, you do not adjust the throttle body when you want to set your idle, it’s done electronically.
The CPU is responsible for maintaining your idle speed via IAC & TPS in varying circumstances.
For instance, if you were to get your CPU reflashed after you installed a radical cam & built the top end of the motor, the idle speed would be raised within the new ECU program to offset it to a new parameter.
If you move the TB set screw in or out, the base idle will change. However, the car may try to compensate and run the car at the preset computer setting. If the base idle is on the low side, for example, the idle will tend to "hunt". It will jump around trying to find the correct sweet spot.
An example of a low base idle setting causes a rough or jumpy idle. A high base idle setting will certainly result in a higher idle...but not generally how it’s done. With new components some tweaking along with tuning is done, not for an issue that just “occurred” with no changes made.
The TPS would first needs to be set correctly. The TPS is nothing but a variable resistor, like a volume knob in an older radio.
Adjusting the TPS.
1) Turn car to key on, engine off.
2) Turn on your multimeter on and set to DC Volts.
3) “Tap” the green wire on the TPS with the red wire of the DVOM.
4) Place the black wire of the DVOM on a good grounded source on the engine.
5) Loosen the retaining screws on the throttle position sensor.
6) Twist the TPS sensor clockwise or counter-clockwise to make adjustments.
7) You want voltage to be below 1 Volt: between .75 and .98 is acceptable.
8) Tighten retaining screws on TPS & recheck the voltage.
If you do run into problems, post it & and we’ll work towards repairing it
Take care!
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justinmurray2001...small world, I'm a few minutes away from edmond in Yukon. Recently bought a 2001 automatic mustang GT myself. Going through similar issues you've had and found myself here for help trouble shooting. Good too see a fellow Okie and the coincidence is wild too