Lately my wife's RDX started to roll forward slowly when in Neutral while waiting in many different traffic lights.
I know the street is flat with no incline because in the past in the same intersections it did not roll. Also my MDX does not roll on them.
Does anybody know what causes this?

 

I think you mean "at idle"... Cuz the car should be in drive at stop lights. I believe there are instances of this and I think you have to disassemble the intake manifold to reach our to gain access to a valve of some sort. I'm not clear because I don't have an RDX but hope some one can help

 

I did mean in the Neutral position from the gear selector, not Drive, and yes the car is idling in Neutral and moves forward when it is not supposed to. In neutral the gears should be disingaged.

 

Why would you put the car in neutral at a light!?????

 

I used to do that because it would lower engine idle speed quite a bit. But I realized it was too annoying because I sometimes forgot it in neutral lmao. So no longer throw it into neutral lol.

 

That! And when in drive and throttle isn't being applied, injectors are off!!!!!

 

Yup I realized it was a big waste of time!

 

I do it so that my right foot can relax without pressing the brake pedal.
In any case the original question is why does it roll when the gears should not be engaged, not why I put the car in Neutral.

 

and I answered that. if it's idling funky, you'll have to remove some parts of the top of the engine to reveal some vacuum parts.
I take that back...you have a 2nd gen RDX with the J-series v6. your problem is you're putting in neutral and letting it roll.

I was thinking you had a 1st gen RDX with the turbo and had a vacuum leak which would cause a funny idle and sometimes accelerating at idle.

also, we cant inspect your vehicle over the internet...because of this... no one knows really what you're speaking about...cuz no one puts their car in neutral at a light

 

WHICH allows the vehicle to roll.

 

Yep - you THINK the ground is flat, but it obviously has a slight slope. The car can't pull itself in any way if it is in neutral.

 

it could be like a 1.5% grade slope. or even less than that, which would still allow the vehicle to roll without its gears engaged.