My car is a 2004 AT. In recent months I had suffered from intermittent unstable idle. It would raise to 1200-1500 rpm in N gear when car completed stopped. The dealer changed the throttle body, airflow senser, checked the vaccum, spark plug but the problem remained. The high idle rpm can be improved if shift the gear to D but I noticed it still higher than ususal (800-950). Is there anyone help?

 

You mention they changed the spark plugs. Have they changed the ignition coils? If not that is the next most likely problem. They only last 30-40K miles.

 

I forgot it. They did change my mazsport coil back to factory set, but the condition was not changed

 

I hope you still have the Mazsport coils.

Sounds like you have an auto.

We have had some problems with a neutral switch in the MT's and hunting idle.

Yours is just idling high right?

 

how's your MAF sensor?

 

they changed your throttle body for a hunting idle? wtf? the spec for idle is 750-850 so if your idle sits at 800 most of the time with an occasional run to 950 id say its probably just a dirty maf.

dont bother shifting to N at a stop just leave it in D

 

MAF, MAF wire harness connection. Dirty air filter. Could be a vacuum leak somewhere too.

 

After the change of the throttle body, they change the MAF sensor (50000km), but it did not work. After one week the condtion reappeared

 

Mazsport coil works well for me still
The problem occurred at randaom timing, Some times all day long but ceased when I reached dealer shop
It also threw no CEL