Idle dip when coming to a stop
 

Hello,

I've noticed from reading the short term fuel trim on the accessport that when I come to a stop, there is a point where the short term fuel trim goes from around 0% to -10% then bounces back up to 0%. This is causing the car to have a small shudder when coming to a stop. What would be the cause of this? I never realized what was happening until I got the accessport. The car has always done this so it has nothing to do with my tune. Any ideas? Thanks!

-Lawrence

bump. ive had this problem too. no accessport to document anything other than the idle dipping down. funny thing is it always happens at the same traffic lights and most other times nothing happens at all. car runs fine in every other way i can think of.

Total shot in the dark.................clean ESS, clean MAF, do 20 brake pedal stomp.

Assuming you have MM's tune and can get his attention, he may have much better information as he knows the AP inside and out.

ok here is what I find driving my R3
the ECU opens the throttle body just a bit when the car is moving so the engine braking is not that strong slowing down the car much.
I notice when in neutral, if the car is moving, ECU revs up the engine about 200 rpm. as long as I am about to stop, it goes back to normal idle.
just a thought.

Happened to me a lot at stop lights and then I would have an extreme loss of power when taking off at the light. But that was before I got my engine replaced and hasn't happened since.

I had tiny tiny vibrations after that, but then I cleaned my MAF and it was all good.

Thanks for all the replies! After doing some more investigation by logging with the AP, I found that the idle dip happens because:

When off throttle and coming to a stop, the engine calculated load is about 23%. However, once you near a complete stop, the engine load increases to about 32%. This shift in load causes the AFR to change enough that the engine starts to take away fuel (around 8-10%). However, the AFR becomes too lean at this point and then the engine decides to dump in some more fuel to achieve the correct AFR. This causes that shudder in my case. I fixed this by calibrating the MAF in the voltage ranges that the shudder happened. In addition to that, I also smoothed the fuel VE table values in the low load low rpm section. I have been driving around for a few days with these settings and the shudder has not happened yet. I hope it stays that way!

-Lawrence

Idle dip is completely normal for rotary, search on these forums for multiple posts throughout the years of the same issue but you can't really call it an issue. I've had my car a couple of years now and it does this normally throughout the day as I drive it. Won't stall but idle goes way low sometimes after I let off the gas and come to a stop. Totally normal guys.