Sluggish start/abnormal engine roar
 

07 6sd RX8 GT with 64,000 miles. Well maintained, oil change every 3k.

Two and a half weeks ago, my 8 was sluggish to turn over and took 3-4 seconds to crank. The normal purr of the motor while inside the cabin turned into a deeper rumble that was distinctively noticeable in all gears at higher RPMs. Vehicle also felt slightly underpowered. All signs clearly pointed to a weak engine. Check engine light was not illuminated

Performed 2 diagnostic checks prior to compression check but yielded no issues or trouble codes. Vehicle failed compression test and Mazda honored the extended warranty with a new engine. In addition, I replaced all spark plugs and had throttle body cleaned and serviced during the transfer. Mazda stated sluggish start was due to a poor battery, so I purchased new battery as well.

Picked up vehicle two days ago only to drive it right back to the shop today for all the same reasons. Still no CE light. New engine and new battery accomplished nothing.

Any thoughts or ideas?

When was the last time you replaced the coils? When getting a new engine people generally replace coils and plugs together to make sure everything is going to be running smoothly.

They've never been replaced. I'll call the dealer tomorrow and request a replacement. However, I've read several threads with a similar issue with replacement coils being the recommendation, each response was that it came to no avail.

People usually replace coils every 30k miles or so, and don't have the dealership do it. Do it yourself for probably 1/3 of the price it is not very hard.

Might be your clutch is giving out.... Happened to me.