I have a 2003.5 G35 Coupe 5AT that I have had since 65k miles and now it has 110k miles. I (and the first owner according to infiniti maintainence records) take very good care of it and do routine maintenance such as synthetic oil changes every 5k or less miles, regular air filter/fluid changes, only use shell premium gas, bg44k fuel system cleaner a few times, spark plugs changed, oil/belts/break/tire pressure checks, etc.

I recently at 105k miles had to replace a failed transmission unfortunately and for no apparent reason I can think of especially since I understand that is very unusual to go bad on these cars.... I did so with a re-manufactured (very expensive) one that has been working great.

My question now is I have noticed since I got the new transmission that the idle is different. I do not know if it happened immediately after it was installed or after because I just started to notice it recently. What happens is that when I am in drive at a full stop or even sometimes in park I notice a little rumble/vibration in the steering wheel/floor. I put it into neutral and it is gone. The RPM at idle stays around 650 and does not move at all in idle. Sometimes its a little worse than others and it also seems to vary some based on the incline of the car. At no time is it especially distracting or extreme but it just is something I don't remember being there before.

Any ideas?

 

Take your sedan back to where they installed your trans, something isn't aligned correctly. Your idle being at 650 rpms at warm idle is a little high, try an "Idle Reset" s/b very close to 500....SEARCH!
Gary

 

I will check it again later. I know it is somewhere in between 500-650. Which seems to be about where its always been. Also I have a coupe if that makes any difference.

 

idle s/b 650+/-050

 

I have made no mechanical modifications to the vehicle and it runs great its just what I described. As soon as the pedal is released it is completely smooth.

 

Mine also does the same thing sometimes and mine's a 6MT. For me it occurs when I'm slowing down to a stop (in neutral) at stop lights. The idle drops a little lower than normal and it vibrates a tiny bit as if it's about to stall and then goes back to normal. For my previous cars it was merely just turning the distributor cap. However considering that it may be transmission-related seems a little alarming.