Ok so I have the 2008 Mazda 3 Hatchback .... I have around 15k miles on it and have taken very good care of it. A few weeks ago I went to start up the engine and once it ignited the RPM went up and back down ... sometimes it fully shuts off and sometimes jumps back up from a very low number. What would cause this fluctuation? This only occurs when the engine has sat idle and cooled off.

Any input is valuable. Thank you in advance.

 

If it's an 08, it still has a warranty and you can take it to the dealer.

The car has a fly by wire Throttle body. It is Computer controlled, perhaps it's malfunctioning.

 

pretty much its this...Mazda tried to fix something that wasent broke and just created more problems, it could be as simple as a bitchy sensor to something like the ECU not receiving the right signals...if its throwing a code try going to a garage to see if they bring it up, then take it ti the dealer if problem keeps occurring.

 

Thx for the input ... yea i thought it had to be a sensor or comp misreading or malfunction as it is only doing this when cooled off. Its just a problem of actually going to the dealer ... more than likely they will lump a bunch of unneeded adjustments like tire alignments ... wish i had my own comp to actually do work on it myself =(

Once again thanks for the replies.