2004 GP: rear defrost -> rpms bounce

[MSUGrandPrix]

Help! I will be honest. I don't know too much about cars, but I do like to make it a point to educate myself.

I have a 2004 GP with 5,000 miles on it. When I turn the rear defrost on I feel the engine shudder, the lights dim momentarily, and the RMPS bounce. Sometimes they bounce once or twice, but sometimes they will bounce repeatedly until I push the gas. The amount of bouncing seems to be greater when the lights are on.

I took it in last week and they said they checked the electrical system, battery test ok, charging ok. Traced to Voltage drop across ignition circuit. R&R ign. switch. Repaired bent loose terminal. This did not help.

I also took it into the shop a few months ago. The blower motor was cutting out when I turned on the windshield wipers. They replaced blower motor wire, removed power fee from Terminal H (connector C210) ran new pwr wire from C210 to battery terminal positive. fixed the problem. Not sure if this would lead to the new problem.

Can anyone tell me if they are aware of this problem and how to fix it?

Thanks so much!

[radeck]

I used to have the same problem on my 99 gp. Rpms bounced sometimes, espaecially when radio was on and i just started engine. I didn't really pay attention to this. Since that time I replaced fuel filter, spark plugs and wires and battery. I'm not really sure which one helped me, but It's been already about 12k miles since that and no more bouncing. You seem to have everything almost brand new, so i really don't know if rreplacing anything will help. One more thing.... first try fuel injection cleaner and maybe premium fuel for few days. This may help too.

[adblink182]

battery. Not enough power to meet the demand. Does the boucning RPM level out soon after?

[MSUGrandPrix]

When we had single digit weather I thought I noticed that the car shudder when I was idling at a stop light, this surprised me (the car was already warm), the first time it happened I thought I was imagining things. I called the dealership's shop and they said that unless the svc engine light came on or I could be more specific they would not be able to track the problem. I started paying more attention to when the car was doing this and noticed the correlation with the rear defrost. Unfortunately we have not had weather that cold since then.

But, to answer you ??:
Sometimes it bounces for just a second (once or twice) and returns back to where it was previously. Last night while idling at a stop light it bounced a number of times (5 or 6) slowly, unfortunately the light turned green and I had to go. I am not. The mechanics said they checked the battery and it was fine- but who knows.

thanks again for the help