I'm new to the forum but I have been reading on here for the last week trying to figure out what is wrong with my car. I have an 07 GT Convertible and my alternator went out Thursday of last week. I had the diodes and brushings replaced. My car idled smooth for 5 seconds and surged for 3, etc. Today, I decided to change my fuel filter since it hasn't been changed since I purchased the car (yes, I know. It should be changed every year.). Once I started my car it still surged. I've read basically every single thread on the forum pertaining to surging. I'm at my wit's end and my pocket book is looking very skinny. Thanks!!!!!!

 

Go to the parts store and buy a7 dollar can of throttle body cleaner. Over time you get a build up on the throttle body that restricts air flow while idling, the computer automatically adjusts for this as it's happening. When you changed your alternator you reset the computer and erased the data it was using to run smooth with the build up. give the throttle body a good cleaning and it'll purr like a kitten

 

^
THIS!

I had the same issue, but it also died on me at the light. And even got the car in LIMP mode. My throttlebody was gone though, according to the dealership. Next time however... I shall clean my TB!

 

I cleaned my TB. Still surging. When the car surges, the lights dim, rpms go down, and you can hear the fuel pump. When I took the TB off, the butterflies weren't sitting flush. They were actually at an angle. Is this how they supposed to be? This is the first time I ever had to work on my car and not sure how the butterflies are supposed to fit.

 

You also have to be careful what TB Cleaner to get. Newer TB's have a coating from the factory, so you have to get the cleaner for the newer TB's. That way the coating won't get eaten off. Also, you may have a dirty MAF sensor. Just after the Air Filter, which you probably already know. But, buy a can of MAF Sensor cleaner, and try that. Be CAREFUL with the MAF Sensor, cause it's very delicate, and put it back exactly as you pulled it out. I hope this helps?......Also, the butterflies set at a slight angle to let enough air into the engine so it can idle.

 

You have an electrical problem. Either the alternate I'd not making enough juice or the battery is toast.

 

I hate auto correct.
Either your alternator is not working properly or the battery needs replacing. Probably both.

 

I have read other threads that people had said they lost low end because of their alternator going out. If cleaning the throttle body and the MAF sensor didn't help then this could be the next step in trouble shooting.

After you cleaned the TB and MAF sensor did you disconnect the battery for 15 minutes so that it could reset again?

 

you can get bad new parts. it happens. take the alternator out and battery and take it to a parts store and get both tested to see if they are working fine. that will be the cheapest way to cut the two out if it is not one of them. i know o'reilly's checks both. good luck. hope you get it fixed

 

+1
There may be nothing wrong other than having to drive the car 50-100 miles to allow the ECU to re-learn the idle strategy.