ponytime11

Hey all,

I recently bought an 02 Mustang Gt 4.6l and now it has a rough idle. I looked through the threads and couldn't really pin point my problem, which is why I am starting a new thread.

The problem is a rough idle. When I start it up, it will run about 700-800rpm and then it will drop down to about 500rpm or lower and act like it wants to die(but doesn't). On the other hand, when I have the A/C on, the car idles fine with no shake or drop in RPM's.

Also another thing I noticed is when coming to a stop(with clutch pushed in or car in neutral) the car will drop to 1000rpm then when I am almost completely stopped it will drop very low into the 500rpm range and there is a noise like it is holding back exhaust then blowing it out. There is also a pop noise in the exhaust when sitting at idle that you can hear pretty well.

Sorry if this was talked about in another thread. Please any help will be appreciated!!

Trint

Soldier GT

welcome to the forums...

JC316

Possibly the IAC valve need cleaning. You need to check the car over though, I have seen people open up the EGR valve to "make it sound cammed" and it can cause issues like this.

stevednmc

Eeek...People do such odd things!

I agree with the IAC diagnosis. But it is recommended to be replaced, not cleaned, but you may get lucky.

Also, have you tried resetting the KAM(Keep alive memory)? Disconnect the battery for 15 minutes or so, then reconnect it and drive it. This will reset the idle trims in the ECM. Try that and see if there is any improvement, if that doesnt work there are tests for the IAC, and their posted here abouts (mostly by CliffyK).

rygi23

Is it making a funny french horn sound coming from the intake? Very good chance it's the IAC. Waiting on mine to show up, lol. Rockauto has the best price. If it's not that, which it probably is, it'll go sometime anyhow and it'll narrow down the source of the problem so you might as well get it.

ponytime11

There no noise coming from the intake. I did take off the IAC and cleaned it, but the problem still persists, so I will replace that. Any diagnosis on the exhaust sound? Again, it sounds like it is holding pressure then when I come to a stop it will like "blow' it out for lack of a better term. When sitting at idle there is a low sounding popping noise, a muffler shop around here said it might be a soft spot in my muffler that is making the noise, but I am not to set on that conclusion.

Thanks for help y'all.