First is is it normal for our cars to dip a bit in rpm and vibrate more when the heater is on or the car has the lights and heater on ? Also I read some on mpg on a few threads here but I seam to get around 200 miles on a full tank of gas I drive 16 miles total to and from work and that 90 percent freeway is that normal ? I know a lot goes into the mpg but I can never seam to crack over 200 also I fill up when the fuel light comes on I end up putting 13.5 gallons of fuel into this beast I figure I am getting around 14 to 15 mpg.

 

Welcome.
I'm not an expert, but I'll tell you what I know.
Vibration issue is not normal, possibly a motor mount issue.
I average about 14 mpg with very enthusiastic driving.
About 150 miles on 3/4 tank.
You really shouldn't let your fuel level get below 1/4 tank.
There are issues with fuel pumps overheating and fuel starvation that can actually damage your engine.

 

15mpg freeway is not normal. See this post in the new owner's thread for what you should start testing/inspecting for potential replacement: https://www.rx8club.com/new-member-f...4/#post4533702

Vibration sounds like a failing motor mount.

 

Thanks for the input any other way of telling if it's the motor mounts ? It's not a terrible vibration I just notice it when the car has the heater turned on like in the am before work to defrost or de fog windows. Also the fuel mpg I think I'll take her on a long freeway trip after a fill up I live in wa like from Seattle to Portland to gage the highway mpg I do like to get on the throttle tho. But I'll also check on the other reason mpg might not be as good .

 

If you have excess vibration at idle and the rev needle stays stable, then it is pretty much always motor mounts. A bit more vibration with the HVAC system in use is normal, so if you have more than normal with it off, then it gains even more with it on, it's still probably the motor mounts.

 

Yeah the vibration only seems to occur when I have the HVAC system on could it be the battery I had one dealer tell me my battery was no good it was underrated and another dealership tell me that it was just fine one told me it was 525 cca The other told me it was 578 CCA I believe it's a 75 d battery

 

No, your battery isn't causing vibrations in the car.


If you have the wrong battery though, you should correct that.

 

The vibration with the heat on is the extra load from the AC compressor. For some reason, it runs with the heat on (lower vents). If it does not vibrate with the heat off, my guess would be that the mounts are OK. Or, I have been driving the last 80,000 miles with a bad engine mount....

And, um, welcome...

Check out the items in the congrats thread below. They may just smooth the idle enough that all is good.

 

Thanks green i figured that might be it I am only at 57000 miles on mine i also just thought maybe the battery was not strong enuff to handle all the accessories on at onetime i was told it was under rated for the car. but thanks guys for all the info your post on the web site are life savers for a lot of us.