I've had my SE for 3 years and have always been able to keep it idling well. I'm familiar with https://www.nellump.net/peri/solving...-problems.html and I've set the TPS many times before but I'm struggling now and could use some advice.

Recently, the car started idling too low. When coming to a stop, sometimes the idle would sit at 800 for ~10 seconds, then slowly drop to as low as 600 while slowly beginning to surge between 600 and 1000. This does not happen immediately when coming to idle. If I set the idle in my driveway I can get it to sit at 800 no problem, but it soon starts dropping again. Opening the air adjust screw more and more doesn't seem to have much of an effect, and it'll idle too low even with this screw all the way open. I do have to turn my TPS screw clockwise further than I should 'by the book' to avoid having the RPM hang around 1100rpm when returning to idle.

At the same time this started happening, I started getting surging when I turn on the AC. The idle surges consistently between 1000 and 1300 rpm when the compressor is on, even if it's not surging at idle with it off. If I unplug the ACV, the surging goes away, and the car idles about 100rpm higher than a normal idle, as it should. For now I am driving with the ACV unplugged but I know it's not right.

I have cleaned and reoiled the throttle body and cleaned and tested the BAC/ACV.

Do I need to start messing with the little throttle stop screw at this point? What would cause the car to idle too low despite the TPS being set correctly?

 

Well, it sounds like you've addressed the most common factors having to do with surging from an -SE. That said, I adjust idle using the Throttle Stop Screw located to the right of the Throttle Body as you're looking at it from the passenger side. This is a smallish screw with a flat blade notch cut in it that's designed to keep the throttle plates from closing entirely, and is located just to the LEFT of the TPS. You may want to replace this screw with a larger head machine thread screw to make it easier to adjust idle once you see how effective it is at that task. The Air Bleed screw at the top of the Throttle Body does next to nothing, and I leave mine set at about mid-way, and never touch it. For fine idle adjustment, it may work dandy - but for everyday, I-need-this-engine-to-idle-correctly kind of stuff, you need an instant adjustment. Once you have a longer screw in place there, it's very easy to adjust the Idle RPM by as much as 100rpm every 1/4 turn of the screw, up or down.

After you set the new idle speed, re-test your TPS position. The Bypass Air and Air Control Valve (BACV) is an on-or-off proposition; it either works to bump up idle speed when your A/C compressor kick on, or it doesn't. If it's working to perform that function, I'd leave it alone for now. Its function in the idle circuit is minimal, though leaks here can allow fluctuation. The other thing to check is your Air Tube connections which go between the Air Flow Meter and the Throttle Body - if you have a hole or a bad connection, it will allow unmetered air into the system in the path of least resistance.

As a last resort, there's an Idle Mix Screw located on the passenger side strut tower that can be adjusted to affect idle QUALITY, not idle SPEED. An overly lean mixture at idle will cause hunting, a similar condition to surging, which you describe. Have a look at those things, and report back if still problematic.

 

I made some progress tonight. It took me about an hour to get the lock nut off that tiny throttle stop screw. I guess you need a tiny 7mm wrench that I don't have, but I got it.

After about an hour of tinkering, I wound up with the throttle stop set slightly higher than it was before (more screwed in, higher stop). I found that I could mostly eliminate my idle surging by setting this screw. However, I still got surging with the AC on until I tinkered with the air adjust screw. For me it still has a pretty big effect on idle. I could minimize the surging if I set the regular idle to around 900 using the air adjust screw, which means with the AC on it would usually idle smoothly at 1100. If I drop the idle with the air adjust screw to 800, it surges with the AC. I'd still like to get it back to 800 but I guess I won't complain.

In some instances, idle still drops low and surges when I come to a stop and apply a small load, such as hitting the brakes. Maybe 5% of the time. It happens 100% of the time if I unplug the vent solenoid/vacuum solenoid connector. Do these solenoids ever go bad? Or could this intermittent drop and surge point to a vacuum leak somewhere connected to that?

 

 

You need to test it with a proper rotary compression tester. The 13B EGI engine found in the GSL-SE is not prone to failure. Have you tested the solenoid on the emissions rack that helps with vacuum when the a/c is activated? Have you adjusted the BACV?

 

I am trying to find someone with a rotary tester here but haven't had any luck so far. I know Mazda can do it but it's pricey. I'll take the schraeder valve out and give it one more shot. I've taken good care of this engine the past 3 years including premixing the whole time, and it had 100psi compression when I bought it, so I'm a little surprised it's giving me trouble now. It's started having a very hard time starting hot so I still think the compression is low.

I haven't tested the solenoid yet, but I can't get the car to idle well for more than a few minutes with or without the AC. I didn't know there was a way to adjust the BACV but I'll look into it if my compression turns out to be ok after all

 

Contact Steve at www.rotarycompressiontester.com He will rent the unit if you choose not to buy one. I bought one and it was one of the best investment that I've ever made.

 

Rotary Resurrection
Morristown, TN,
1 hour east of Knoxville.

Rotary Resurrection home of the budget rebuild.

 

I got additional compression results with a different piston tester and I removed the valve. Both rotors had 3 even spikes. Peak compression (schraeder valve in) was 95 front, 80 rear. I don't know my cranking speed so this feels like a gray area. The service manual says this could be acceptable if the cranking speed is on the lower end. I might buy the rotary tester just to have it since I have 2 rx-7s, but I'm stripping the car down to paint in less than 2 weeks and I'm trying to decide if I should pull the engine first so I can paint the whole engine bay too. I'm not sure the rotary tester would arrive in time.

Also, I drove the car about 10 miles today and it idled fine with and without the AC, although it was around 950 instead of 800 with the AC off. I guess I've made some progress tinkering with the TB.

Any thoughts on what I should do next? Just pull the engine anyway, or deal with it later and keep driving it? Again, I'd prefer not to have to pull it before I paint it, but if it has to get pulled anyway then I may as well.

I plan on rebuilding this engine myself when the time comes. I've always wanted to rebuild a rotary but was too chicken to do the FDs myself when it died...

 

I've heard good things about them and they're close by, but I'll definitely attempt to rebuild this one myself. Thanks

 

Signs of low compression are usually an inability to hot start, as the engine housings have expanded and the seals aren't doing a good job anymore. This can be overcome by pull-starting the car with another vehicle, and is a pretty good indicator. Also, a low battery (or poor conductivity in the cable leads and grounds) will result in low cranking speed which will exacerbate low compression. If the engine is running fine now, I'd leave it in and paint the thing, but that's me. Pulling an engine later is not difficult on an -SE by removing the hood.

 

I think I finally figured out what was happening. A check valve on the intake manifold was broken, and it goes to one of the barrel shaped solenoids that control the ACV. It didn't appear broken until I took stuff apart, so my guess is that sometimes air was getting through the crack and other times it was sealing ok.




I do still have signs of low compression, so I decided to go all-in and do a complete restoration of this car. I pulled the engine, transmission, and most under-hood components out yesterday so the engine can be rebuilt and the engine bay can be painted along with the car. This should be fun...

 

I'm curious if your problem was ever resolved, as I am having the same issue. My car idles fine with A/C off but surges with the A/C on. I can hear the ACV click just before it starts surging. I'm also familiar with https://www.nellump.net/peri/solving...-problems.html and have tried everything listed there, including replacing all the vacuum lines.