Ladies/Gentlemen,

I have already searched for a similar issue and was unable to find anything relevant. Hoping someone may have ideas about the minor issue I have.

Background:
I have a 2006 6Spd RX8 with ~4K miles on the engine (purchased new). Did my own oil change at 2800 miles and all recalls/TSB's are up to date.

Issue:
Sometimes, after moving the car without warming the engine up, I rev to 3K RPM's for ~5 to 7 seconds to avoid flooding. I have noticed the engine starts to vibrate and emits a noticeable shaking sound when reving the engine up to 3K RPM. Once the engine warms up, this goes away (typically after 1 to 2 minutes of running the engine). This does not happen every time I start the car. The car is not throwing any CEL's or lights and the car runs fine otherwise. The only issue is this intermittent shaking noise shortly after car warm-up (while reving the engine). I have a pretty good dealership, however am afraid they may have difficulty reproducing the issue (if I try to show them, the engine will be warm, etc.). Anyone have any similar experience or pointers? I am not overly concerned, but just want to make sure this is not indicative of a greater problem in the making.

Could it be a loose plug wire, coil, etc. that could fix itself once everything begins heating up? I cannot think of any other possibilities.

Thanks in advance for your help.

 

Depending on the temperature range of the plugs you have, they could be misfiring due to fouling until they get some heat in them.

If I am remembering correctly, higher heat range plugs operate better when the engine is hot/very hot, but the down side is they do not work as well when cold and this can cause more misfires due to fouling.

Could also just be that your plugs are just carboned up some, which would show more when the engine is cold (again causing misfires)

 

Thank you for the feedback.

The plugs were replaced when I purchased the car (last September) - I believe under a TSB (I did see the list on the Finish Line Performance site) and so could the plugs already be fouled? I do redline the vehicle at least a few times every time it is driven and I am pretty meticulous about proper care of the engine (break-in, warm up, revving before shutting down cold, etc.). Also, would an intermittent misfire throw a CEL?

 

Missed the mileage - plugs should not be fouling so soon.

Are you sure you are keeping the RPMs to just 3000? The reason I ask is that the ECU will limit RPMs to about 5000-5500 while the engine is cold with fuel control which would sound like misfiring if you try to exceed. This is an engine protection issue to keep you from over-revving until the engine is warm.

Could also be something simple like a loose plug wire, bad gas, etc..

 

I am sure I am keeping them to 3K RPM. Also, the car is always in a garage and so the temperature stays relatively constant (compared to sitting outside). I do not believe it to be bad gas since it has done it on more than one gas tank. I am thinking a loose plug wire, however am somewhat suspicious of this cause since it consistently goes away after a minute or two. I will inspect the wires this evening (maybe the dealer did not install them tightly when they replaced the plugs). I just wanted to see if anyone else has had a similar issue and , if so, how it was corrected.

Again, thanks for the input.

 

Answer here is truly dependent upon how cold "cold" is, but it may be that you need to get a little heat expansion in to the rotor apex seals. Otherwise you may not be getting a full seal and as a result not seeing proper levels of chamber compression for full detonation of the incoming air/fuel mixture. I have seen the same thing on my 03 build over the 3 winters I have run it here in NH and this condition is very common for me. Until the engine is warm I baby the heck out of the tachometer.

 

hey guys im a newbie so dont make fun of me ok.n e way i was having the same problem with my 8...i would start it up and rev it a little and you could just feel it vibrate really badly.took it in to the dealership and turns out i needed some new motor mounts...if you are still under warranty why dont you just take it in to mazda and have them diagnose it?