V6 (1994-2004) Mustangs Technical discussions on the 3.8L and 3.9L V6 torque monsters

04 Mustang 3.8 V6 Idle speed

Old 03-05-2012, 02:22 PM
Thread Starter
Join Date: Mar 2012
Location: Texas
Posts: 1
Default 04 Mustang 3.8 V6 Idle speed

Hey all,
I have an 04 3.8 V6 mustang and I'm noticing the car idles pretty steadily between 800 and 1000 RPM even after the car is warmed up to normal operating temp. It just feels odd to me because all cars I've owned idel at about 500RPM when the engine is warmed up.

Another thing I notice is that the RPM gauge jumps to about 1500 when the A/C compressor kicks in for like 1 second and come back down to about 800.

I was wondering if anyone else with the same car had the same idle rates and the same behaviour when the A/C compressor comes one.

Any help is appreciated.

M0E is offline  
Old 03-18-2019, 04:03 PM
Join Date: Dec 2015
Location: Texas
Posts: 2

I have this exact same problem, anyone have any info on what it could be before I start tearing it down?

kapone86 is offline  
Old 03-18-2019, 04:05 PM
Join Date: Dec 2015
Location: Texas
Posts: 2

Yes it is supposed to kick up when the A/C is turned on for a second or two and then come back down, but the idle itself isn't supposed to be that high. I have the exact same year v6 mustang with the same issue.
kapone86 is offline  
Old 03-19-2019, 03:20 PM
Join Date: Jan 2018
Location: Pennsylvania
Posts: 2,326

There is a RELEARN idle trim process. You should do it any time you change the intake,
or tune the car. It also involves turning on the A/C in the steps, but I didn't do that, I just
let it learn the throttle trim from cold to operating temperature. Since you have an IAC,
it will still learn.

Wait till the engine is cold.
Disconnect the battery, and touch the + to the -.
Reconnect the battery and start the car, and let it idle to operating temp, about 15 minutes.
Then turn the A/C on, and wait a few minutes.
Turn the car off, and on, and the idle should stabilize right away.
Turn A/C on to test where it jumps.

If you still get the same problem, you may need a new IAC valve.
08'MustangDude is offline  
Related Topics
Thread Starter
Last Post
The Racers Bench
10-01-2015 08:31 PM
New Member Area
10-01-2015 08:00 PM
Motor Swap Section
09-14-2015 10:29 AM
V6 General Discussion
09-07-2015 07:39 PM

Thread Tools
Search this Thread
Quick Reply: 04 Mustang 3.8 V6 Idle speed

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites.