So my 12a '83 is having a bit of a problem with idling. The idle fluctuates and backfires very quietly, kind of a sputtering sound like air out of the exhaust. I don't know if this is related, but it also has a hard time starting when warm. It will start, slowly, but when it does it won't hold idle at first without me using the throttle. I replaced the fuel filter and it didn't fix the problem. What should I check next?

 

Had literally the exact same issues with my 85 carburated gs. Took a rebuild of the carb (may not have been NECESSARY but familiarized me with the damn thing), a few bottles of marvel mystery oil, a few bottles of seafoam, and most importantly...deletion of the stock emissions setup. Also, look for holes in the exhaust near the front of the car, especially in the 2 air tubes coming up from the converter area to the intake. Not sure if the car (yours) has had this problem or just surfaced. But either way, i recommend getting rid of emissions and RE ROUTING the vacuum. There is an entire write up on the deal here on the forum. I believe the source I used was a separate site with great pics which I was referred to from here.

 

Sounds like either a vacuum leak, or a mis-adjusted or dirty carb, causing your engine to lean out at idle & while starting.

Is your manual choke working properly? Do you use it when starting? The choke also opens the throttle slightly for cold-start.

What's idle RPM? If set too low, idle becomes unstable in that way, too.

Some small idle instability is not uncommon for a stock rotary with emissions gear on it; they were tuned to run as lean as possible for smog purposes. But it should hold stable idle without throttle input if adjusted properly

 

I do use the choke when cold starting, but not for when the car's already warm. In regards to a potential vacuum leak: When the hood is open and I press the throttle I hear a faint(kind of farting-ish?)noise coming from the air intake...

Now that there's been warmer weather it holds idle when I start it but it is still rough and sputtering. Idle speed fluctuates around 750 but isn't ever smooth at a specific number.

 

Check the #2 anti-afterburn hose for leaks.

https://www.rx7club.com/1st-generati...estion-750125/

 

I *carefully* checked the hose when the engine was hot and I couldn't feel a crack.

 

Try tapping on the top of the #2 afterburn (thats what is making that noise your referring to) valve while idling. Check the rest of the system for leaks.

Before you start eliminating the emission system, just buy a couple packs of vac port caps, and process of elimination cap off the ports to identify any changes in idle.

Check the linkage for binding, missing parts, or slack. Check that the choke cable has a clip holding it in place, for it prevents the cable from being stuck open.

Check your ECU fuse also. You'll know because your choke **** wont remain out when cold if pulled out.

Try installing a FRAM G-2 inline fuel filter under the hood, so you can confirm fuel supply easily. (walmart $3).


Did this happen all of the sudden to a daily driver, or a problem that slowly developed to a weekend cruiser. These guys can help, but as much info you can give the faster youll have it fixed.

Watch out for the yank around.

 

What exactly am I checking for when I tap on the #2 afterburn valve?
Also where is the ECU? I didn't even know that I had one...
I've had this problem ever since I bought the car, which was Fall 2012.

Could this rough idle be a sign of worn apex seals?

 

So, looks like the problem has been resolved. Turns out I just needed to give the carb a good tune. This was successfully achieved with the help from Sterling's guide here: https://www.rx7club.com/1st-generati...e-carb-310927/

Looking back I probably should have tried this first...oh well.