Jay W

My 924S has been running rich for a long time and I am now trying to fix it so it will pass emissions. I have possibly traced the problem down to the auxiliary air valve not closing all the way when the engine warms up. I completely blocked off the hose running to it and it seems to run cleaner, but at the same time the idle has slowed down to less than 500 RPM. I did a search on testing the valve and people suggested crimping the hose to see if it changes anything. I am wondering if a correctly functioning air valve is expected to bypass a small amount of air when it is closed, which raises the idle speed somewhat? And has anyone totally blocked the hose leading to the air valve and noticed that the idle speed is extra slow on a warmed up engine? The valve is under the intake and I dont want to replace it if it is working as expected. Thanks in advance!

SoCal Driver

Running rich is not the idle control valve. The DME sets this as well as the time the injectors are open.

Better check your fuel pressure. Also check all of the small vacuum lines going to the fue pressure regulator and the fue damper. Could also be your engine of air temp sensors or the AFS. At the worst it could be a leaking fuel injector.

Jay W

Vacuum lines are all connected and appear to have vacuum when taken off the fuel pressure regulator and the fuel damper. I checked the fuel pressure a while back and I think it was ok. I did try to make the engine run extra rich by pulling the vacuum line to the FPR while I was watching the voltage output of the oxygen sensor, and when it was pulled the car seemed to run the same. Strangely it doesnt blow black smoke or bog down like other cars that have bad fuel pressure regulators. I will check the fuel pressure again. I was thinking about checking the air temperature sensors. Im I correct in thinking that the fuel pressure leakdown test will help diagnose a leaking injector?

shmucklebuckle

Check for vacuum leaks and replace hosing as neccesary. Then hook your car up to an EGA after it's up to temp, disable the idle air control valve using step 3 at Clark's Garage - Idle Speed Adjustment, and use the air-bypass screw on your AFM to adjust the mixture. There's a plug on the top that needs to be drilled and removed to get to the screw, and the screw is a 5mm allen. On the EGA, you want everything under "1" to pass smog with flying colors, in CA anyways (100 HC, 1% CO). You'll understand when you look at the HC and CO gauges on the EGA. Also adjust your idle bypass screw on the throttle body in this "diagnostic mode."

This eliminated my high idle after warm up, and a "cough" every second or two from running waaay rich. And I replaced fuel filter, lines, regulator, dampener, and had injectors overhauled by Witchhunter Performance. I also replaced almost all vacuum lines, rebuilt my throttle body, and replaced the o-ring in my venturi. None of which fixed my high idle and rich mixture. Clark's Garage has walkthrough's for almost all this stuff.

edit: seeing SoCalDriver's post below reminds me: I also replaced plugs, wires, rotor, cap, and made a new battery to block ground cable. That didn't fix it either YMMV

SoCal Driver

Pull the fuel rail off and lay it on some rags. Use a jumper to run the fuel pump. The fuse block on the 924S is under the dash on the left side. Jump Aux fuse #2 to #3. Count from the door. The Aux fuse block does not have the plastic cover on it. This will run the fuel pump. Check the tips of the injectors.

Another reason for running rich is poor ignition spark. Some after market plug wires will cause this. If you still have the stock wires then the insulation may be cracked or one of the balasted connectors at a plug may be breaking down. While expensive I prefer the stock wires and connectors. Check the rotor and cap too.

If you have the numbers from the test that indicated high HC post all of the numbers including the CO and NOx.

All the idle control valve does is bypass the throttle body. It does not let in outside air. So the AFS "sees"
all of the airflow into the engine. If you have a serious vacuum leak on the engine side of the AFS it will run lean as the AFS is not seeing all of the airflow.

Mark-87-951

could the 02 sensor going bad cause this? Ive been having trouble passing emissions. After the first time I sealed the TB, replaced a defective TPS, serviced the fuel injectors and only failed by .04 on the next test. I've had poor gas mileage for awhile and the exhaust is fairly sooty so I have an o2 sensor on the way.

Jay W

Well first of all thanks for all the good advice so far. I will look at all the things mentioned here. It did have some old crappy platinum plugs in it at the time of the test. I have since replaced them with bosch supers because I had heard the platinums dont work well with our cars. The exhaust smell is still as bad as it was before the plug replacement so I dont think it made the car good enough to pass emissions. I did however replace the O2 sensor before the test and it had still failed. Crazy thing is the car has always started and run very well but the exhaust always had a 'partially unburned fuel' smell to it. The emissions numbers were:

HC 2.24
CO 9.22
NOx 4.39

shmucklebuckle

It can. That was a guess of mine as well for my rich issue, because the O2 sensor isn't used until it heats up (1 wire sensor heats up from exhaust temp, takes longer... 3 wire sensor has built in heater, heats up and is used much sooner). I replaced it, but it also didn't fix it for me.

shmucklebuckle

Definately adjust your mixture with the air bypass screw on the AFM like I described above. If your systems are all in order, you should easily be able to bring those down to 1 (HC and CO). Took me about 1/2 an hour, including the warm-up lap . If you were local I'd say come use ours at the shop (svc dept, m.c. dealership).

Jay W

Thanks for the offer, yet another reason to be local to California! I will get some time to work on it this weekend and post whatever fixes the car so I can pass on the info.

shmucklebuckle

Sure Good luck.

The DareDevil

Did you check if the cat is still installed? Maybe the previous owner emptied it out.

shmucklebuckle

A better flowing exhaust will lean out the mixture... so that would only help

The DareDevil

Removing the CAT will result in a more powerful exhaust smell. What I'm saying is he may be failing because there is no cat (regardless of the rich condition). Running rich, however, is not helping the situation.

shmucklebuckle

This is true.