Mazda 6 engine revving really really fast in neutral

mazda
mazda6

#1

I own a 2005 4-cylinder Mazda 6 sedan with 105,000 miles. In the past 2 weeks, I have encountered a problem where the engine seems to rev at very high RPMs. The first time it happened was on a very hot day. I had just returned home in the car from a 6 hour drive. About 3 hours later, I again drove the car. I noticed that, while driving on the expressway, I could take my foot completely off the accelerator and the car maintained its speed of 65 mph for about 1 minute. When I got off the expressway, I had to apply much firmer pressure than normal to the brakes to stop the car, and the RPMs remained high (1500-2000 RPMs—normally reduces to less than 1000). I shifted the car into neutral while stopped, and the engine started to race between 2500 and 3000 RPMs, cycling about every second. It sounded like I was getting ready to start a drag race (vroom…vroom…vroom… you get the idea).



The second time it happened, it was again a very hot day, but I had not been driving the car long. Same thing happened when I shifted the car in neutral at a stop light. I got a really nasty look from the woman stopped next to me because she clearly thought I was challenging her to a race! I have the car at the Mazda dealer today, but their initial inspection revealed no codes and they haven’t seen anything like this before. There are a few other points I can make:

--I was running the A/C, but turning it off had no effect.

--I checked to make sure the accelerator wasn’t stuck on the floor mat (it wasn’t)

--stepping on the accelerator in neutral did not reduce the RPMs

--both days, the temperature was above 90 degrees

--the check engine light has not been on



Does anyone have any suggestions about what to do about this? It is a much cooler day today, and the mechanic cannot replicate the effect. No codes come up when they check the car with the computer.


#2

Ask the mechanic to show you where the idle air control (IAC) valve is - normally easy to find once you know what/where one is.

Keep a hefty screwdriver, small block of wood, or rubber mallet in the car. The next time it does this, stop safely off the road, put in park & apply the parking brake, pop the hood and give the IAC a good whack or two with the butt end of the screwdriver - or whatever. See what happens.

You could also ask what they want to pull the IAC and clean it - it could help. At the very least the wiring for it should be checked.


#3

Cigroller this is EXACTLY what is happening to my car in the “self-revving engine” discussion. It must have something to do with the heat, mine only does it when I have been in a traffic jam and my engine is hot hot hot. I did not have luck with the IAC but I have not fully cleaned it yet. The difficulty is that I am in traffic so rarely that I would not be able to immediately tell if this is the problem. Cigroller what do you think about the heatsoak to the cruise control cable theory that I posted in my string?

rjb did you check the IAC? Have you fixed your problem? PLEASE let me know what you did, I actually had to pull over the other day because my engine was overheating. Not ok.