04 RX8 won't idle, Throttle body failure?
 

Hi all,
I just joined the forum, looks good! Hope you guys can help me out.

My Rx-8 has always idled low(700-800rpm), and stalls quite easily when taking off. I've assumes this was the nature of the engine and did not worry about it.

Now a problem has developed to where the engione will stall when its warm, as soon as the clutch is depressed, but funny enough this does not always happen.

I got it checked out at the dealership and they say the throttle body is damaged and needs to be replaced ($650 for the part alone)

Now I have a mechanical/electrical engineering background and started thinking about what could be wrong. The car drives fine other then the idle so my thought is there could be a bad spot around the idle position in the potentiometer that tells the ECU about the throttle position.

Anyway that was just a thought and I'm looking forward to hear if any of you have had similar issues?

cheers,
Sander

The positioning sensor for the throttle body is built into the assembly.
So if the sensor, motor, or valve components are bad, the whole thing needs to be replaced.
Do you know why they thought it was the TB? Did it fail a diagnosis test?

Do you receive any CEL and if so, what are the codes?
If you want to try a couple things with the TB, I would first clean it.
Just use Carb Cleaner and a shop rag to wipe around the valve.
Open the valve with your finger and wipe around it.
I usually remove the four bolts holding the TB to the UIM to clean it better (no need to remove the two coolant lines).

Then you can visually watch the valve open and close to see if there are hesitation or "skips" while traveling.
The valve is controlled by a stepper motor, so simply have someone in the car, turn the key to 'ON' (no need to start it), and have them press and release the gas pedal.
Then watch the valve open and close.

I just got this car a week ago.....
My 05 RX-8 with 30k miles will idle around 1000 at start up. I always let the car warmup to operating temp before I drive.
Today I noticed it dropping to 800 and then back up to 1000. It never dies, overheats or makes loud noises. But with the drop in rpms the car shudders slightly(maybe im just worried). Car seems to have plenty of power and I get it to redline every day.
So Is this normal?

A bit of idle wonder is normal rotary behavior

If it isn't the TB...
What about the other sensors?
Neutral and clutch sensors?

He doesn't appear to be experiencing similar symptoms with a bad neutral switch that we hear about.
With him mentioned the car stalling when warm... guess we couldn't rule out compression either.

thanks. didn't want to highjack the post it just seemed that i might have an issue i didn't want to expand into a bigger problem.......

idle issue
 

Thanks all for the replies,

To Jon316G, the TB error has been diagnosed by the Mazda dealer, they could not give me a more detailed description of what exactly failed.

What is a CEL?

The car drives fine at anything above idle, so I don't think there is a mechanical problem with the engine.

I'm taking it off today to give it a good clean and check the operation like suggested. Also I will measure the resistance of the potentiometer to see if there are any abnormalities.

I'll keep you guys informed

P.s. somebody mentioned a idle circuit, does this car have that? It seems unnecessary to have this on an engine equipped with DBW?

got my car back from the shop and guess what? It runs perfect now! They decarbonated the intake system and replaced sparkplugs under warranty.

I guess the throttlebody was just dirty/plugged.

I'm sure you've heard it all before:

Don't blindly trust on your dealer's advice..