Hey guys, fellow S4 FC3S owner here! And guess what!? I have an odd idle issue.
 

I own a 1986 RX7 with a practically stock engine minus -
Opened (honeycomb removed) cats
straight exhaust with rear mufflers deleted and 2 tips welded to the OE piping.

It also has little suspension, but that isn't why I'm here! This car, since I've owned it (about 1 year) has had a very odd idle problem that I have yet to put my finger on. I've read and read and read and eaten and read more. But I can't seem to find my symptom listed any where, and not sure where to go.

Basically, after the vehicle comes down from its high idle for cold start (and still idles about 1300-1500 while temp gauge hasn't moved) the vehicle has a random "hiccup" if I may call it that. It is random to the point that it is hard to explain via text. Basically, every few seconds, it kind of "pops" but the RPM gauge continues to read steady. I hear it in the exhaust, but do no show any deviation in idle from the tachometer.

That being said, recent maintance/work that has been completed to solve his issue has been the following - new spark plugs, idle air adjustment, rich/lean mixture adjustment (per the beautifully written stickys).

Any ideas here? I have also noticed that only one of my extra port valves really doesn't open. I used a dab of paint pen on each cylinder of the valve and drove it down the road to over 4500 RPM to see if it'd move. One does, other one doesn't look like it moved as much.

I feel like I'm all over the place SO, TL;DR -
Idle issue sporadic during cold idle and into warm idle/ random "pop" that happens every 3-4 seconds.

Any input would be great, thanks!

Seems normal to me. Mine pops wile idling. Sounds good

Sounds pretty normal. Maybe you have low comp? Post a video with good sound of the misfire, should help a lot.

yeah because idling at 1500-1800 is normal....faceplam.

The idle speed is high for sure, is the car completely coming up to temp? I.e 1/4ish up the gauge? If so, feel the rubber lines for your BAC valve, if they are both hot to the touch, this is a good thing. Other possibilities are thermowax not working right, TB coolant ports blocked, maladjusted throttle or cruise control cables

EDIT: Vacuum leak is a possibility, but usually that gives you a "loping" idle.

Also, the little "pop" that you hear is fairly normal of a rotary with straight through exhaust. The motor could be getting weak, but if the idle isn't correct or the TPS isn't set right it will make it do that as well

After my FC runs for about 30 seconds after the high rev it starts dropping to 1000 and back to 2000 continuously. I'm assuming its something to do with the thermowax valve

1badvert

Mine has been doing the same since a recent intake manifold change, but my BAC "clicks" everytime the RPMs drop, I think I may have a coolant bubble in it, or its gasket is leaky, just haven't had time to really look at it yet

So I'm assuming everything is normal. If I have time in the shop, I will try to do a compression test today to see where I sit for compression.

I hear about the 1200 being high idle, but I only assumed it was doing this while "cold" due to a cold start routine the engine would go through. After it gets warm, I have it idling at about 800 RPM, and it's only "problem" is the written off popping of the exhaust. I figured that would be irregular, but thanks for letting me know that it's just witchcraft!

Thanks for all the info, I think I may look into doing the pellet soon, too. Seems like a pretty straight forward process. My next issue will need to be to find where I'm losing coolant.

After about a week or so, my coolant light and buzzer goes off when taking a hard right turn, or holding a right turn for more than 5-7 seconds. It goes off when I shift the car back left.