Hi Folks-

I searched already, and found a few posts on idle surge, but I have something specific to add that I hope will help pinpoint the problem.

I'm new to rotary, so bear with me.

Once the engine warms up, I get very crisp idle surge, very consistently varying between 800 and 1500 RPM. When I put the engine under a load (turning the a/c on, as long as the compressor is doing its thing.) I can replicate this 9 times out of 10. What specifically causes this? I suspect there's a vacuum problem somewhere, but with the crispness of the surge and the ease of stopping it by putting the engine under load with the a/c, I'm wondering if there's something in specific that I can look for.

I've had the car about a week, and this started happening very abruptly after about 400 miles. I've made no mechanical changes to the car during that time.

Car runs like a raped ape once I'm on my way...strictly an issue at idle.

Thanks in advance for your advice.

Chris

 

The test procedures for a surging idle is on F-225 in the factory workshop manual. If you don't have one do yourself a favor and get one.

 

Or this

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/94-fsms-available-download-449950/

 

Thanks fellas. I have a copy of the manuals, but I don't have the SST for the job....as a more roundabout way of helping if you could point me to where I can get the SST (i think it's a 'self diagnosis checker, it's difficult to see the SST code in the manual) for the job that would be cool.

Additionally, the manual isn't consistent and points to a boatload of different things that it could be based on the vague description "idle fluctuates/idle hunts."

(page f194-195.)
Check the ISC
check the spark plugs
Check the primary injector
Check the ignition timing
Check the throttle sensor

Then, you have page 225 which gives you in addition:
check for service codes (I don't have the SST)
check coils,
check igniter,
check ecu terminal voltage,
check PCV valve,
check fuel pressure.

Previous posts indicate the the throttle sensor is another good place to look.

I could do an engine swap in the time it would take to check all of those things properly, so I was hoping that someone would have had this same problem before, and where putting an electrical load on the engine stops the surge immediately and could help out. If not, no big deal, I'll go through all of it. I am just hoping to leverage the millions of hours of experience embodied by this forum.

If anyone can help narrow this down based on my description, I'd appreciate it.

All the best,
Chris

 

You can check engine codes without the SST:

http://www.fd3s.net/engine_codes.html