My car used to idle perfect, at a solid 750-800 rpm all the time, but recently it has started to develop weird idles, which is totally random. Sometimes it will not drop below 1500 at all, even if the car is completly warmed up, and sometimes it will idle normal at a solid 750-800. But at other times, it will idle at 500, and once the idle dropped so low it stalled itself.

When it idles at 500 I noticed the volt gauge drop down to 12 (half way), and if I rev it will jump back up to 15 (3/4's of the way). Any ideas what would cause this? Oh, and at redline the check engine light will sometimes come on, but it's not throwing any codes when I check.

Thanks in advanced for any help!

-Minh


*edit* S5 GXL, 146k miles

 

1)check operation of BAC valve, intake for leaks, TPS
2)normal for the alt volts to fall off at lower than normal rpm's- the alt's not spinning fast enough to maintain 14v

 

There should deffinatley be sticky at the top of the 2nd gen main page that says FIXING IDLE PROBLEMS in big illuminous letters. On average theres about 5 posts each week which ask for help fixing a dodgy idle and all of them get the same replies. Its either check the usual -tps, bac, thermowax/fast idle cam, intake leaks etc or 'there is a search function you know'. There was a thread a short while ago in which someone brought up the problem about users posting questions about a specific problem, getting lots of replies for possible fixes then not coming back to the thread to explain if any of the fixes worked. Dodgy idle threads are a perfect example of this, if you do a search you get 10-15, or maybe more pages with something to do about a weird or dodgy idle. Only a few of these actually go into detail about idle issues and possible fixes. The point in my rant is not to bash users who ask for help in fixing idle problems, or users who don't return to finish there posts(i know i've been guilty of that in that past). I just think a sticky would be a good idea as we all know how common idle problems are with the fc.