S4 Idle issues with AIR pump removed?
 

So after doing my research I determined that the emissions could be removed from my S4 safely without any negative affects. I started by only taking my AIR pump off since it was such a eyesore and a large chunk of engine bay. Every since that I noticed my idle was a little surgey and would dip and rise consistenly while at idle, but not terrible. Now, a couple weeks later, however, my idle is HORRIBLE, I sit there and the car shakes sporadically and the idle is all over the place between 750 and 1k, quite a few random misfires as well. It wasn't until I googled "AIR Pump RX7 Idle" that I see posts talking about how the stock ECU compensates for the false O2 sensor reading and removing the AIR pump will screw up your idle.

Im just wondering how everyone else seems to do it. Is everyone investing the $1200 to get a SFC when they remove their emissions? Just dealing with the horrendous idle? When I asked around initially everyone said the only downside to AIR pump removal was a bum cat, which my cats are all gutted due to being previously melted. Is there some sort of workaround that I don't know about? Someone said just disconnecting the O2S but that doesn't sound right. Id prefer to leave it off, along with installing the rest of my emissions block off plates, without getting involved with a whole standalone ECU system right now. What am I doing wrong here?

Put the pump back. On your NA engine, the air pump is what mechanically controls the entire engine. This is why turbo 13bs are completely different. Turbo guys don't have the same pneumatic controls because of forced induction and no vacuum actuated ports.

Damn. Only future hope is going standalone? Cause Im trying to make a 180-200whp N/A track car with a nice simple engine bay. That air pump is a large hunk of bleh, plus a parasitic draw on the engine, and a good 10lbs of weight.

the air pump pumps air into the exhaust ports at idle, and some of this goes into the engine. so when you remove the air pump, idle speed drops and quality gets worse. you can raise the idle and adjust the mixture screw but it will idle better with the air pump

It also provides the pressure to open your secondary port actuators and change the manifold airflow at higher rpms, which are in your powerband. Without them, you just get air through the primary ports.

I thought in the S4 the intake actuators were operated by exhaust backpressure? Not AIR pump pressure?

Would there be any way to make it better with say an SAFCII?

Have a look at the s5 na manual. The system diagram is much clearer and more organized, but seems to maintain the same general features. Some of the electric solenoids on the vacuum system are used for vacuum controls, but some are actually in the positive pressure control systems, used for controlling the vdi (for better upper range), as well as the sleeve actuators. Have a look, especially at page F1-6 of the s5 na manual. I helped a guy put his na car back together this last year because he thought he didn't need any of that stuff, sold it, and the thing ran like a 1920s tractor. On a turbo car, things are completely different. Na cars need this equipment unless you go full aftermarket ecu, etc.

I think on the S5 that stuff is operated by AIR pump, but on the S4 I'm fairly certain that its all operated by exhaust back pressure, hence the RB headers and presilencers being different for 86-88 to provide "adequate backpressure for functionality of the aux ports"

Either way, I think I've got a failing coil that could be causing a lot of my issue, and I did adjust some idle settings that didn't seem to do much until later that day. Maybe that's the cause. Cause before it was ok.

You don't need the air pump or ACV on a S5 car( If your cat's gone). Mine has been gone since 1998 and it's always ran and idled just fine without them. I did leave the rats nest in place and just plugged any unused hard lines though since it's a pressure system and not connected to the vacuum system even that's probably unnecessary. I'm still on the stock ECU. I didn't have any idle problems until after the street port and I got that sorted out as well.

You're correct the 5th and 6th ports are controlled by exhaust backpressure but there is still a solenoid that controls them I think. Not sure as I've not looked to much at the S4 stuff. I know people manage to get them to work on the S4 without an air pump or acv but I personally don't know how they did it. How are your vacuum lines. A vacuum leak could be causing you problems as well.

Intake and vacuum system are 100% sealed. Hooked a big ol smoke machine up to the intake boot and let er rip. Not a single trail of smoke anywhere.

I think a good 90% of what im interpreting as bad idle is this damn random misfire, and im sure its gotta be my coil, seeing as how it just neglects to fire sometimes apparently.

Either way, I'm at the shop late tonight, suppose ill toss my AIR pump back on real quick and see if it changes anything, Here's to the one time you hope the part DOESNT fix it!

Well, out of all the easily replaceable parts I could have lost for the AIR pump, it had to be the stupid lower hose that changes size midway through. So until I can get that (I might have an extra in my garage) im stuck

Just out of curiosity, if the ECU is trying to compensate for the O2 sensor getting air from the AIR pump, wouldn’t disconnecting the sensor put it into a base (albeit very rich) idle map? Because I disconnected it for the drive home and noticed zero change as to how it was running

I'd get that misfire taken care of first and go from there, and reconnect the O2 sensor. I will try to look at the differences between the S4 and S5 cars later but I don't see why a S4 car couldn't be gotten to idle fine without it. I do seem to recall there were two connectors going to the ACV that I removed what they connected to from the ACV and tied off to the side, but I think this was just to make the ecu happy so the check engine light would go off. That was 22 years ago and I don't remember if it's still set up that way. I'll look into that sometime later as well.

Ok, I took a look at the car and it's still set up the same way. Looked at the FSM and I think it is the "Split Air Solenoid Valve" and the "Port Air Solenoid Valve". They are plugged in and zip tied to the harness out of the way. IIRC they didn't effect my idle since the things they controlled in the ACV was gone. I just had the CEL on and got trouble codes with them unplugged hence I plugged them in and tied them off out of the way. This is on a S5. I'll have to download the S4 FSM and look at it but it sounds like the S4 uses these as well. I sill feel you should be able to get your idle issue sorted out and still have no ACV. I had a buddy at the time who set his car up almost same as mine and IIRC his idled fine as well. His 6port sleeves and rods were removed then like mine are now.

Well I actually still have my ACV hooked up, haven't gotten the block off plates yet. Could that be an issue? leaving it hooked up with no AIR pump?

Maybe. When those solenoids open to inject air into their respective locations and there's no positive pressure coming from the air pump I'm not sure what will happen. If at that point it creates a "leak" of sorts then it may cause problems. May be the cause of the idle problem you're having. You could unplug the electrical connectors to the solenoids and see if that helps. May get a check engine light. If your CEL comes on but it helps your issue may just have to drive with the light on till your block off plate gets here.

it could be. if i'm trying to diagnose problems here, i usually make a gasket with no holes out of a soda pop can

Well I got a set coming soon, so I’ll just hold out til those get here