Car intermittently shakes at idle only when A/C is on
 

Hi there, I tried searching for this on the forums but didn't see anyone else posting about it.

My 2005 6spd RX-8 (about 128k miles) will shake periodically when idling and when the a/c is turned on. It's the kind of shaking you get when the car idles at a really low RPM. It shakes for about 5 seconds, then it stops shaking, then it'll start shaking again about 45 seconds later or so. When my a/c is turned off, the car doesn't experience any shaking when idling -- it's just normal idling. Turn the a/c on again and the intermittent shaking resumes. I dont know if the RPMs are being affected or not; I dont know if the RPMs are dropping at the exact moment the car starts shaking or if they're increasing or going back to normal when the shaking stops. I can't recall and my fiancee has the car right now so I can't check.

Any ideas? Is there anything I should check for? Thanks for your help!

This is fairly common with all cars. Using a/c puts more load on the engine and at idle it may cause the RPMs to drop down until more fuel is injected to re-stabilize the idle. I wouldn't worry too much about it, unless it is causing excessive problems. This is an electrical-related problem so you could try cleaning up the grounds, battery terminals, etc. Another member might be able to chime in and give you a better solution.

Are you in your original engine? If I can recall, I started to experinced that shaking when I was close to 150,000 miles on mine. I did as suggested above and also replaced my whole ignition system which helped. What I would worry more on is if your engine couldn't handle the load and turning the A/C would eventually cause your car to stall.

Check the motor mounts.

Check Motor Mounts, Coils, Spark Plugs... Rotaries in general dont like idling so... IMO Rotaries aren't designed for the street applications... They work great in Racing environments...

Most likely your motor mounts

interesting, i dont recall having this problem on any other car I've owned with over 100k miles (which happens to be all my cars lol).

I believe the previous owner replaced the coils, spark plugs, and wires about 3k miles ago.

I take it most of you experience this shaking too when idling with your air conditioning on? The whole car shakes when it does it and it produces a really low-pitched rumbling sound.

What should I check for when inspecting the motor mounts? What will they look like if they're damaged vs if they're fine?

I had this problem, sorta, plus some of my IC piping rattling against the subframe from time to time at low RPMs - 700+/-

I've since increased my idle to 950 RPM and no longer worry of either.

Your motor mounts should be solid and well formed. It's fairly easy to inspect them from under the car.

There is a TSB for checking that. If I can remember, drive the car then while you are decelerating in third gear at less than 3,000 RPM and about 30mph, quickly floor the accelerator pedal; if you feel a shake and very noticeable hesitation occurs, it may indicate that your engine mount(s) is/are worn.

An engine mount can be worn without any visual defects. At over 100k miles, chances are they are in need of replacement.

Drop the Air conditioner
 

New to this rx8 site. I have a question. Can I omit the A/C from the power train by simply removing the belt?. Will I draw a cel?. I never use the A/C and I figure it might give me a little more get up and go.

I have owned it for 4 years now. It's a 2004 series one 4 speed automatic. Just runs superb but thought I could get more power by droping the A/C I don't use any way?. Any one ever done this.?.:):yelrotflm

Yes

No

There is NO additional drag on the engine when the A/C is off. You do NOT need to remove the compressor belt. Just leave the A/C off...

@peteInLongBeach: Thx:), it was just a thought. Always looking for more what I call Driveability which isn't always more horse power. I just made my own ran air set up and took it on the freeway to test ad was a notice able response. Also interested in serpentine belting of the rx8, maybe some lighter pullys for unsprung torq. Having fun:


A woman walked up to me last Sunday after skating was over and said "Is this your second child hood" referring to my 8. I responded: NO this is still my first". He he he.

I have this promblem when the heater is on or the a/c it happens when either the compressor kicks on then off or the fan kicks on or off just alittle vibration. Then it goes away then comeback on