Hi Everyone
I tried searching for similar problems, and didn’t find any related posts. I am hoping that someone can help me figure this out.
The car is a 2005 Mazdaspeed Miata (turbo) with 30,000 miles. It has not been babied. It has been autocrossed a few times, and I like to dirve it like it was meant to be driven. That said, I always let it warm up before I drive it hard, and give it a minimum 60sec cooldown before I turn it off. And my wife, who’s car it really is, is very good about this as well. She never drives it hard, by the way.
Anyway, I was driving tonight and everything was perfectly normal for the first 5 or so miles. During that time I did not get on it at all. Then, turning onto the main road, I gave it a flat footed blast to 40 or 50, shifting near redline. As soon as I came off the gas, all hell broke loose. The engine went really rough and backfired a few times. It continued to run like this, and if I put the clutch in it really wanted to stall. I managed my way into a parking lot and gave a quick look around, nothing was obviously wrong, and the gas cap was tight. Temp gauge stayed normal as did oil pressure. The CEL did come on (I won’t be able to pull codes until tomorrow at the earliest).
The car started back up, a little harder to start than normal. But it is much louder, still running rough, and definitely has less power than normal. But I don’t hear any strange noises like lifters or rods, etc. It is driveable to 2000 rpms (albeit poorly), but if pushed past 2000 it starts surging and backfiring. At stop signs sometimes it will stall and sometimes it will manage to keep it alive.
One extra piece of information. When I got home my wife got really nervous and confessed that she put regular (87 octane here) gas in; the manual specifies premium. Since the gas station she uses is right near the house, I wondered if it is possible that the car ran fine because it was driven easy, but once I got on it the deficiency of the regular caused the problem. I suspect that is wishful thinking, but it is the only thing I have right now. I know the tank was pretty much empty when she filled it, so its all 87 at this point.
Any thoughts would be appreciated. I plan to try and get some of the 87 out and try to replace with 93, but that looks like it won’t be easy thanks to what seems to be a strainer on the filler neck.
-Dave