97 Sunfire, New Alternator now no idle

[indakeys]

I have 97 Sunfire with a 2.4. Has been a wonderful, reliable car. Yesterday the alternator stopped working. I jump charged the battery and the car drove home without any other problems. Today, I installed the new alternator with no apparent issues. BUT, when I started the car, it has a surging idle from 400-1000 rpm. It surges very quickly. The check engine light came on and the traction control light came on.

I drove the car and it runs fine above 1200 rpm going down the road. Seems to shift fine. But returns to surging idle and/or stalls at a stop.

I know there are a million (literally) posts about the 2.4 idle problems. But I cannot connect any of those to this problem which definitely started with the new alternator install.

Thanks for any help!

 

[melsg5]

You have to go to autozone or similar parts vendor that will do a free computer scan to see what code you have.

 

[indakeys]

Problem solved. Wanted to share the solution in case anyone else encounters the same.

Apparently, when limping home with a bad alternator, the system voltage lowered to point that the ecu was losing reference signals. One of them was, apparently, the IAC. This threw the code, and the IAC was left without instruction where it stood. The plunger was extended just enough to be thrown on and off its seat by the engine vacuum and airflow. I removed the IAC, plugged it into the car and turned on the key. (I was truthfully only trying to verify that the motor worked) The motor immediately extended the plunger completely and then retracted back to normal. I reinstalled the IAC and the car runs like a dream again. Apparently, the ECU needed to fully extend the IAC to regain its reference. I still have to go to Autozone to get the code read and cleared.. But, the car started running great just as quickly as it had died. Not very sophisticated, but it worked and would be very easy and harmless to try if you have the same symptoms.

If the code references something else, I will post it here.

 

[melsg5]

Thanks for the update