Is it normal to have hesitation while RPM fall?
 

Hi all,

'95, stock besides downpipe and catback.

Searched around but didnt really find anything.

When I rev the car in neutral (up to say 2500-3000), then let off the gas, there is a little bumpyness/hesitation/shudder @ ~1400 RPM, like right before it falls to idle. I can see it on the needle, and feel it in the car.
Roommate noticed it without me saying anything to him.

Is this normal 'rotaryness' or something else?
I do not believe this to be the 3k hesitation because what I am referring to happens after letting off the gas.
It never really has a 100% smooth fall back to idle.


further, not sure if related, if i play with the pedal around that rpm range (~13-1500) I often get a loud pop out of the tailpipe.
I figure it runs rich being a '95 to be on the safe side, but not sure if that explains/is related the first part.

I have a video around here somewhere if this isn't clear.

Appreciate all input

*While RPMs fall

Would be a better title

My 93 does the same thing. Full turboback exhaust with an intake and efini Y-pipe. I just assumed it was the mods which were the reason it did it. Subbing for the solution.

Too weird. This is the first thread I opened after opening a Ninkasi

But on a related note, had the same problem with a stock ECU and mods. PFC helped, but has it's own issues (i.e. idle)

My FD has a similar issue where it does not like to fall back to idle smoothly (or at all). It will sometimes do so slowly or irregularly, or sometimes even hang at around 2000 rpm before shuddering a bit and then go all the way down to idle. Accompanied by pops out the exhaust a lot of the time.

Can't figure out logically what the heck it might be and I don't really feel like replacing stuff at random is productive. Hoping others with more experience chime in.

*Edit: usually if I jab the throttle a bit I can induce it to fall back down to a reasonable idle, but that is not always the case. More pops out the exhaust.

**Edit 2: I have a Pettit Unlimited ECU, BNR turbos, downpipe, and catback exhaust.

Found the video
 

Took this vid a while back but never got around to posting about it

https://youtu.be/IXfMHVB-FBw

Just watch the needle behavior below 2k and at one point u can hear a minor pop

Normal. There is a dashpot on the throttle that slows the throttle closing towards the end. If its sticking, then your idle might stick slightly high. Otherwise, looks fine to me. Rotaries are kinda bumpy.

Matt

Hmm I suspect this is a culprit, do I even need the dashpot? Might just pull it off and see what happens. My understanding is that it just slows the throttle closing for emissions.

It slows the throttle plates closing to prevent afterburn. It's in the FSM :P. The ISC is also supposed to perform anti afterburn function. If you disconnect the ISC and try revving it like that again it should pop a lot more.

Matt

That's usually the tune/decel fuel cut but worn/broken motor mounts and differential bushings can also cause it.