I have a 2005 5speed tC. Last night as I was driving in fourth gear, I took it out of fourth and put it into neutral to coast into a parking lot. I happened to glance down at my tachometer and noticed that it dipped to 800 and then shot up to 1500, back down to 600 and then up to 1200, back to 800 and then back to 1600. Even as I stopped the tach was fluctuating a little before settling down to normal idle of 800. I drove out of the parking lot and sped up to 3rd gear and then coasted again to see if I could recreate it. Sure enough, the same thing happened. Today, I went for a drive to see if I could reacreate it. It's back to normal behavior of idling at 800 when I take it out of gear and coasting.
So what do you guys think? Is this supposed to be normal? Was my ecu making adjustments last night to what the timing should be? I want to take it back to the dealer, but I'm sure it won't happen when they drive it.( That's my luck). I did put in half a bottle of Redline fuel injector with the last tank of gas I used, but I am halfway down the second tank of gas since the fuel injector cleaner. I hope this behavior is normal, but if not, I want to know what to tell the dealer to look for before my warranty runs out!

 

That's pretty nromal to keep it from dying.

 

dirty maf?

 

dont worry, this seems to happen when the ecu is in its "learning" process. i noticed my tc tended to do that after i reset the ecu (disconnected battery).

 

Although I don't have fluctuations like that after my first cold start in the morning, it should be normal. The first few cold days here my tC was bouncing from anywhere between 800-1200. Not a big deal, but it did happen - it was the tC's first "real" encounter with the cold so I wasn't surprised.

 

Pirranha, it is just now starting to get cold here so it may be the MAF adjusting to the colder air.

 

I keep my car running almost always for atleast a minute (normally 2-3 min) before I even put it into gear. My car does that also untill its warm but yes - mine sometimes dips below 1k and then goes back up to 1100-1200 for a sec. Its all good. I thought there was a problem but the dealer said there wes no issue and I also learned that its ok. Now if your car was stalling out or the RPM's going up a lot higher then that ....then ide say there was an issue.

 

lol yes... if your engine suddenly starts spiking the RPMs and keeps bouncing off the rev limiter everytime you put it in neutral, then there may be a an issue... just maybe