[trevnut]

My girlfriend has a 2004 mustang gt automatic. Car will run fine in then all the sudden when you come to a stop the idle surge from 300 to 1500 and sometimes the car will die. Then you can drive down the road from that stoplight to the next light an it will be perfectly fine. Then It will go to crap again and stay that way for a while and then be good again and then bad and then good.

I have change the IAC and looked for vacuum leaks. There is no check engine light onit and I don't know what else to look for.

Thanks

 

[wmburns]

First thing, change the PVC valve. Check the grommet/seals around the PVC valve for leaks.

This could also be a bad TPS, weak throttle return spring, EVAP leak, or other vacuum leak.

For an automatic transmission that dies coasting to a stop but other wise idles great, this could be the lock up torque converter not releasing as it should.

To correctly trouble shoot this, it would be handy to know the TP-MODE PID.

For more information on how to trouble shoot IAC/idle issues:

Is your mustang stumbling, dieing at idle or idling rough? - Page 14 - Ford Mustang Forums

 

[mbpenny]

Clean Throttle Body. I've had this issue before and it was because of gum up on the edge of the butter flys. And if that wont fix the problem check throttle sensor. Again this is just some ideas.

 

[wmburns]

The inside throttle body on 96+ MY's have a note stating NOT to clean with harsh cleaners. There is a coating on the inside of the TB that harsh cleaners will remove. Proceed with caution.

 

[trevnut]

Ok, update. It was surging earlier and I put it in neutral and it continued so I quickly rev'd the engine and it returned to idle and idled fine.

I cleaned the throttle body already. It shouldn't be sticking.

 

[wmburns]

If no vacuum leak, then look at the TPS.

 

[trevnut]

I can't find any vacumn leaks. I bought a tps sensor and put it on. Still does the same thing. I got a canister charge valve code.... could that cause all of this?

 

[wmburns]

Maybe. But who can say without the DTC code?

Remember that a stuck open EVAP value is a vacuum leak.

OBTW, did you clean the MAF? Use only a product designed for the job.

Did you do any of the basic functionality tests called out in the informational post?