OptimusComposite

2005 RX8, 62000 miles. I've owned it for about 1.5 years, put about 12000 miles on it, never had any issues of any sort with the engine. Regular oil changes at 3000 miles with 5W-20, always stayed on top of adding oil between changes.

It's been pretty cold where I live lately, and I've noticed a couple times that if I shifted a little early and tried to get into a gear around 2000-2500RPMs, my 8 would struggle a little bit until I could get the RPMs back up. I assumed it was simply due to the engine being so cold - the problem went away as soon as she warmed up - and just adjusted my shifting habits. Am I correct in believing that this struggling with low RPMs is attributable to the cold. I know the rotaries like higher RPMs to begin with and that there isn't much power down low, but I've never had my car struggle to make power at 2500RPM before.

Jump ahead a few weeks, I have to give my friend's car a jump start one morning, so I start my 8 and let her idle while I jump the other car. I wasn't thinking and shut my car down as soon as I was done - I'm sure my car hadn't fully warmed up, as it was terribly cold and it probably didn't run for more than 5-8 minutes. I went back to her later in the day and she started pretty hard, and then once she got going the RPMs were jumping all over the place and the car sounded noticeably louder to me. I let her run and warm up, but it made no difference. I took her out to drive and found that I had to give a ton of gas just to keep from stalling. Engine light came on and started flashing, things were not looking good. I was able to get up into the higher RPMs and things smoothed out and everything was normal again, but low RPMs were still awful. I got her very warm and then let her sit for a few minutes, and upon starting up everything seemed to be good again, though the engine light stayed on. I haven't had the same problem since that day, so I'm kinda hoping that the strange behavior was my own fault because I didn't warm her up properly - does that sound reasonable?

And finally, the last piece: My gas mileage has dropped by 2-4MPG across the board. On the highway, on cruise at 70MPH I only pulled about 17.5MPG. In the city, I've been getting 13-14MPG consistently. I attribute some of this drop to the cold, what with the longer warmups and the inefficiency of the rotary in cold temperatures. However, the decreased mileage on the highway puzzles me, and to me would point to something more troublesome. I've also noticed that I seem to have lost a bit of power, which I really notice in 3rd and 4th gear lately. I've noticed some of the how-to's on this site (I'm not much of a motorhead, but I'll make do), particularly cleaning the MAF, and will be doing some work on my girl tomorrow. However, I was curious if my combination of circumstances might point to something else worth checking out?

Many Thanks!

Tamas

iTrader: (1)

Yeah... get the code read for the CEL

monchie

Get the code read for free at your local Autozone, and get back to us.

Footman

iTrader: (2)

when was the last time coils/plugs were changed?

OptimusComposite

Hey guys -

Thanks for the replies. I'm not sure how I managed to forget it, but I had planned on getting the engine codes checked tomorrow. I'm hoping that will shed some more light on everything, of course.

As for the coils/plugs/wires, I'd probably have to guess that they haven't been done over the life of the car. I've added them to the list of things to be done, regardless of whether or not they're part of the problem.

alnielsen

iTrader: (4)

If that's the case, you probably need to replace the air cleaner element too.

Footman

iTrader: (2)

Agreed, if nothing's been done, you've got a LOT ahead of you.. coils/plugs/wires, air filter. Don't forget your own health too and check the CABIN AIR FILTER and have that replaced.

Also, doing an application of SEAFOAM at your mileage is not a bad idea.

Footman

iTrader: (2)

There's actually a whole ton of **** you should be doing if none of it has ever been done...

- MAF sensor cleaning
- Battery check (park your car overnight, come back in the morning, check voltage at terminals, should be 12.6 around.... 12.2 is low.
- Alternator check, should output around 13.8 to 14.6 when idling and no electronics are turned on (fan/radio). Turn everything on... MAX AC, CD player, high beam, fog light, and emergency flashers. Alternator should still output around 13.8...

Footman

iTrader: (2)

Inspect coolant, will need to flush soon...

replace your transmission fluids with Redline MT-90
replace your differential fluids with Redline 75W90
Inspect your brake fluid, do you see bubbles? color? viscosity? Time to flush soon.

OptimusComposite

That's a healthy list. I have some pieces of it done, but clearly I've got some work to do. I'm glad you mentioned the Seafoam - I wasn't sure if fuel additives were alright on rotaries or not. I'll report back tomorrow with the results from all these tests.

Many thanks!

shadycrew31

iTrader: (6)

Fuel additives are fine...

I would scratch the mt-90 off that list regular old mazda trans fluid is fine.

I would consider premixing as well...

Also the rotary runs extremely hot unless you are in below 0 temps I wouldn't consider the cold an issue.

I'm guessing your code will be a stuck valve of some sort.

OptimusComposite

Results from the day's work:

Engine code was intermittent/random misfires. Cleared the code and it hasn't come back since, and the car has been running fine. I'm not sure if I had a bit of bad fuel or just moisture buildup in the engine housing (possibly from not letting the car fully warm up previously?), but that problem seems to have resolved itself.

DId a full oil change, cleaned the MAF sensor, and then went for a test drive. Mileage was back to my normal 22-23MPG freeway, so that's good news. I put a can of Seafoam in as well, and will probably continue to mix throughout the winter as a preventative measure. I'll continue to monitor my mileage, but everything seems to be back to normal. Cleaning the MAF did seem to help with idling as well.

I cleaned the air filter and cabin air filter as well. The air filter had been changed ~ a year ago, and it was relatively clean. The cabin air filter wasn't too bad.

I'm going to try to get the transmission/differential/coolant while I'm home from college, and we're planning on doing some brake work as well. Plugs/coils/wires is going to have wait at least a little while until I can clear up that money.

Thanks to everyone who had some input - I appreciate your knowledge. Thankfully I don't think is going to prove to be a major problem!

monchie

^ Take care of it and the car will take care of you, good luck.

Footman

iTrader: (2)

There's tons of threads/discussions on what transmission/differential fluid to use. I recommend you read them and decide yourself what you want.

I'm simply giving you what I use, and in the Canadian climate, Redline MT-90 and Redline 75W90 in the transmission and differential respectively has worked out great for me. Especially in the cold, the MT-90 fluid makes the shifter a lot easier.

My car is 95,000 km now, no transmission/differential problems.

Please read the threads and decide yourself what fluids you want to use.