I have an '05 Mustang GT with an automatic transmission and over 93,000 miles on the car. My right axle went bad and the bolt broke off trying to get the axle off. So we put in a whole new rear end with 373 gears and a Diablo Predator tuner to correct the speedometer so it matches the new 373 rear end.

My check engine light keeps coming on with a P0506 code for low idle speed.

Anyone know what the idle for drive and idle for neutral should be on a 373 geared automatic??

Thanks for your help!

 

I can't tell you the exact idle speed your car should be at, but I do not think the idle speed has anything to do with your rear end ratio. I could be wrong though.

My GT 5 Speed Manual sits around 800 RPM... I'm sure some Auto's will chime in.

 

I'm confused ... what does idle speed have to do with rear end gear ratio?

 

It doesn't. Gear ratio has no effect on the rpms when idling.

 

aint your gears thats for sure cause it has nothing to to with it..... if your car has a tune maybe it freaked out and call who ever you got the tunes from other than that maybe a vacuum line?....... im just throwin **** out there

 

Idle Control System RPM Lower Than Expected
Maybe it just needs new plugs and a throttle body cleaning.
Have the plugs ever been changed?
Has the throttle body ever been cleaned?

 

Wait a second...
Did you load a Diablo tune or just adjust the gear ratio?
If you loaded a tune, the tune might be the problem.
The tune may need adjusting.

 

On my SCT you have to load a sct tune in order to adjust the speedo parameters. That's why when I ordered I had them install a stock tune, as well as performance. I can now run a stock tune and adjust speedo and idle speed as required. If the diablo is the same, reload your stock tune to see what you're oem idle speed was and then reload your diablo tune using the idle parameter adjustments as well as speedo. I also noticed the fan turn-on temps had changed with my tunes so I adjusted them back to stock as well.

 

I have an auto w/ a bama race tune. My idle sits @ 750rpms

 

Clean your throttle body. My uncles 05 kept pulling the same code. I took his throttle body off and cleaned it with some carb cleaner and a rag and put it back on and it has not came back on yet. So I would say that it your problem.

 

Thanks guys for all your help. The car is going up to the mechanic next week and we'll take a look at the options then.

I realize that technically the gear ration doesn't have anything to do with the RPMs but since I never had any issues with the check engine light before installing the new upgraded rear end and tuner to adjust the speedometer to match the rear end gears -- well you can see why I felt that it is somehow connected.

How hard is it to clean the throttle body? Any pics?

 

hose clamp on air tube, 4 mounting nuts and 2 electrical connectors.

 

Yep that it. It's real easy. You can do it and save some money.