2004 Mazda 3, 2 litre manual: Anyone else experience spontaneous increase in RPMs when engine is hot? This has occurred when cruising at approx 2500 RPMs as well as when rolling to a stop at a light. Revs spontaneously increase to over 3000 from 2500 and do not drop to idle speed when foot is removed from accelerator. Only way to bring revs down is by braking while in gear. Sounds like a Toyota issue, I know. Dealer claims never to have heard of this occurrence.

 

Nope. That's a new one... for Mazda, not Toyota/Pontiac of course.

 

only thing i can think of is a sticking throttle plate, try cleaning it NOT WITH TB CLEANER, just a damp cloth

 

Has anyone had the issue where your foot is on the brake and it revs for no reason?

 

Yes, I have. But only when braking hard and my right foot is crossing over the accelerator and the brake pedals at the same time in a heel/toe motion.
Sometimes under those circumstances the throttle pedal feel is so light, I can't feel that it is under my foot.
Pretty easily explainable in my case.
Is this what you are experiencing also?

 

Thanks for your help! Unfortunetly in my case, thats not the problem for me. I will just be sitting there at a light with my foot only on the brake and it will just start reving for know apparent reason!! Someone had told me that it might be a vacume leak at the power brake unit or the air idle control valve?

 

As with most things automotive, it could be a number of things.

Certainly a vacuum leak that only presents itself when engine vacuum is high would be one of them. Here's the scenario:
With the throttle plate closed, as when the car is at idle, engine vacuum is very high. If there is a split or small hole in a vacuum hose it may open up under these conditions. When that happens, idle speed increases and vacuum decreases causing the split to close again. And the cycle repeats itself.
It could be the check valve in the brake boosting system is allowing vacuum to escape as well.
It might also be a gremlin in the MAF sensor. If a wire to the sensor is broken or has a bad connection, this might also cause said problem.
If the MAF sensor (Manifold or Mass Air Flow) is going bad, same-same.
The ICV is out though. These cars do not have one as the idle is controlled by the PCM (computer) which gets its information from a number of other electronic sensors. Sometimes I think it would be a lot easier to have a mechanical valve as opposed to the electronics making all the decisions, but this is the world we live in today.

But as I indicated, it could be a number of things. Start diagnosing with the simple things first.

 

Do you have an aftermarket air intake?