Idle surging after warm up

[GALLY3309]

Hello, I’ve searched and haven’t been able to find a solution to my problem.
I have a ‘93 Mustang GT. It starts and runs great…. for 20 mins that is. It seems when the car enters closed loop the idle drops and surges up and down. I have a new IAC, I’ve cleaned the MAF and TB. I’ve smoked the engine checking for vacuum leaks. I’ve checked and cleaned the ECT Sensor. I’ve disconnected the o2 sensors which I thought helped but ended with the surging idle. I’ve done the base idle reset as well.
I need help, I want to drive the car. Any guidance would be greatly appreciated.

 

[Noobz347]

Procedures and test points are all in the first post of this thread:

Thread 'Help me create the "Surging Idle Checklist"'

Apr 10, 2005

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help.

Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of a systematic process that checks and eliminates possible causes. This idle problem checklist will use the same troubleshooting strategy and methodology.

By the term surging idle, I mean an idle that...

• jrichker
• 1986 1993 86-93 check engine light code 67 cranks ok dump codes eec-iv mustang no start
• Replies: 575
• Forum: Fox 5.0 Mustang Tech

• 

Holler if you have questions.