Engine stumbles on acceleration
 

'04 manual, stock w/ 46k miles. After running a 1/2 tank w/ only MMO to clean, I filled up with only Idemitsu mixed at 1 oz. per gallon. I had some time off work, so it sat in the driveway for 3 or 4 days. Normally I always shift under 4k on a cold start, but I hadn't driven in a few days so I cheated and revved it higher taking off from 1st (I know, the film barrier was reduced further from sitting). Well, it got up to 5.5k then it stumbled down a couple thousand k, immediately jumped back up to 6 or 7k, then down 2 or 3k, then again a third time before I took my foot off the gas. I let it warm up and everything was fine after that for a couple of weeks. I thought it must have been due to the high level of premix and/or from sitting for so long. So I tested my theory out yesterday, this time without having sat for days, and with my normal premix of 4 oz. MMO and 4 oz. of Idemitsu. Again, it stumbled at 5.5k, so this time I immediately let off the throttle before it bounced again. Anyone know what the problem is? I have new coils/wires/plugs, but haven't installed them yet. Could that be it?

I am no expert but personally i think it may be the plugs and coils. My car did almost the exact same thing over the summer and i had 3 bad coils and 3 bad plugs. I would try changing the coils, plugs, and wires first since you already have them, then go from there.

It happened this morning, this time at only 2.5k rpm from cold start.

I asked some non-rotary friends, and one said he didn't think it was coils, that when they go bad they just die completely (in his experience). He said it sounds like a fuel delivery issue. Maybe my fuel pump is going out? Guess it's time to mod for a series 2 pump.

are you getting any Check Engine light? if not, then i think youre putting too much premix in

Check your plugs+coils.

No CEL. I'll do a decarb and swap the plugs and coils and see if that does the trick, thanks.

8 oz pre-mix per 16 gallon tankful is plenty.

Coils do tend to work ok right up to the point of their failure. The only way to know if they're about to expire is to perform the TSB inductive and resistive tests.

'plugs on the other hand can get fouled at any time and would be the first thing I would recommend you address.

Use some fuel treatment, like Lucas or STP, to ensure your injectors are clean as well. Don't pre-mix the tankfull that you use the gas treatment. And cut back on the pre-mix!