Hello, and hopefully a call out to you tuners.
First, my five letter.
1885 RX7GSL-SE 1.3 l 890350 late build with transmission and other improvements, factory AC, push button air select, factory stereo surround joystick, amplifier/equalizer. Stock 1.3L 13B racing beat complete exhaust system with headers. Rebuilt at least once 202K custom paint, accellera phi 205/60 14 stock alloys.
After a bit of tuning and replacing wires and plugs with NGK blue silicone and BR8 plugs the engine runs perfect and has perfect driveability, no B fires, and idles about 850RPM, its warm up characteristics are very good with a high idle at about 1850 and purrs until warm. All this while running the AC since start up. However, once warm it idles a bit low and after stopping at a light sometimes needs a bit of accelerator touch to keep the idle up, this tendency to drop RPM starts after a few seconds and not immediately on letting off the gas, so it does fine, then drops but hasn't stalled, a bit annoying but i wont be running AC that much here, with that big sunroof.
What should I check to see if it functions right with the AC running while hot and temporarily idling? I tend to think that its not advancing the vacuum advance the way it should, maybe need to advance it a bit overall? I haven't timed it it runs so well. the other thing i'd like to report on this car is that no matter how low you let the RPMs drop in 4th gear, if you get it down, coasting to 1000RPM, you don't need to downshift, giving it gas just gets the RPMs back up with PEP, it has a torquey feel, just an example not that you do this but the engine feels so strong you never have the feeling you need to downshift, gassing it gives you the pep, as much as downshifting. Fun car to drive so far with new RB sways and energy suspension all new components, new rear shocks, new tires, new seats and carpet.

 

The first thing I would check is the the bypass air control valve. I would ensure the vacuum line is in good condition and the electrical part is working and adjusted properly. After checking the BACV there are other areas to check but for me, this is the first thing I would check.

 

OK. Checking on this and using the service manual for procedure to check. It runs so well when cold (running AC at start up) that I'm reluctant to make changes ***** nilly. It runs so well with it off and runs well till warm when using AC, acts a little like a vacuum leak and surges when it drops below 1K RPM.

 

When the ambient temperature is above 85 and when using the a/c, the engine in my 85 surges for a second or two when the idle dips quickly with the clutch depressed coming to a stop and then the idle levels out to about 1100rpm a second or two later. I've lived with this issue for the last 14 years since I've built the car. I have been unable to track my issue. Much like your car, mine runs so well any other time that I've decided not to adjust the BACV and just leave it alone. I don't drive the car that much when it really hot out anyways so I decided not to mess with anything.

 

Thanks for the reply. Mine seems to do fine for a few seconds after stopping, then the idle drops and surges a bit in the 6 to 900RPM range and is somewhat inconsistent sometimes acts OK but has a tendency to drop further and surges/recovers, probably from engine idle protection in the setup. I got cold air blowing but will not use the AC that often, other than late summer. The AC portion of the BAC has a lot of adjustment travel, but turning the adjustment screw has had next to no effect in tuning efforts to solve this.

 

One of the best guides I have seen for describing the -SE idle circuit, and diagnosing and repairing -SE idle problems, is a document by David Lane from 1998. See https://www.nellump.net/peri/tech/en...idle_problems/

The document covers a lot of idle problems and their possible solutions. Your problem sounds like a blend of cycling and too low of an idle when the A/C is on. The Bypass Air Control Valve (BACV) and the Air Supply Valve (ASV), among other causes, figure prominently in both problems.

 

Thx. I converted this to PDF just in case the web site goes away.

 

Thanks for converting that page to a PDF. It's also archived on the Wayback Machine at archive.org at https://web.archive.org/web/20220117...idle_problems/.