theDevilX

So sorry if this has been answered before, its a tricky one to search for as everyone seems to use different words for this.

My 12a has a tendency to judder and buck when off the throttle below about 1750 rpm, it sometimes does this at light throttle as well.
Kind off annoying when trying to smoothly slow down in traffic as I have to put the clutch in to do so smoothly. If it carries on then its going to mess up the U joints on my reconditioned driveshaft, plus its just really annoying.

At some point (before I owned it) the car has had an emissions delete, thermal reactor swapped for a proper manifold, air pump removed etc. Although being a UK car we never had as much emission stuff as you guys to start with.

Apart from this it runs well, has good power etc. Any ideas?

mazdaverx713b

iTrader: (91)

I would first confirm that the shutter valve and coasting valve are in place and working properly. The shutter valve cuts fuel to the rear rotor under deceleration and the coasting valve allows fresh air into the combustion chamber to prevent drag from excessive vacuum.

t_g_farrell

iTrader: (1)

Check your motor mounts. Could be a loose one aggravating this. This is a common issue with rotaries at low rpms (and below 1750 is low indeed). I don't even try to engage the clutch much below 2000 rpm, its just not producing enough power to do much at those rpms. Is this the first time you have had a rotary to drive?

theDevilX

The AAV has definitely been removed.
We only had 2 valves on the UK spec cars, one for the distributor vacuum advance (which is still there) and the other which is the AAV.

I don't get any pops or bangs from the exhaust on changing gear, or on overrun for that matter.

I'll check the mounts, I have 2 new ones that I need to get around to fitting anyway.
I get that 1,750 is low, but I'm not accelerating hard from this, infact it only does it on deceleration so it shouldn't matter if the revs are too low for making good power as its not being expected to. In actual fact it will accelerate smoothly from very low revs, so when I'm pootling in traffic I don't need to be revving it, its just on the overrun that it goes crazy. And only below around 1,750.

t_g_farrell

iTrader: (1)

I see you have or had a 2nd gen so you are familiar with rotaries. You should just push in the clutch and not worry about it LOL. Some of the emissions stuff that got removed actually helps smooth that out.

theDevilX

Haha, yeah that would be the easy option. But you're talking to the guy who lifted the engine out of his boat & completely stripped & painted it because he wasn't too happy with a bit of rust and oil stains on it. I like stuff to be right, and stuff like this drives me crazy.

If its something I can fix then I'd like to.

GSLSEforme

What rpm do you have idle speed set? Have you adjusted idle mixture to see if you can help this condition? Are ignition components in good shape?

theDevilX

When fully warmed up the idle is around 800rpm.

Haven't adjusted the idle mixture because I didn't want to to mess up my idle. Rotor arm, cap, plugs & leads are all new in the last couple of months.

GSLSEforme

Turn mixture screw 1/2 turn out(left) and see what that does for your symptoms. No change,turn back(right) to original position and another 1/2 turn right and roadtest again for results.

theDevilX

I'll give that a shot. Cheers.

lwrobins

Is the Vac advance disconnected? I recently started running it on my car. It greatly improves low speed drivability.