Carrera 3.2 idle mixture

[kamaro]

My car just failed emissions, they need at least 3.5% CO and mine did 6.1, when I hooked my wideband gauge it idled between 12.5-12.8 all day long, so I tried to turn the air screw in the AFM counter clock wise but that was not doing anything at all!, it stayed right at that range. The car idles and drives beautifully, except that I cant bring the mixture down to something around 14-14.7 or so.

What do you guys suggest to at least get the car to pass the emissions?

[cabmandone]

I think you have to put a jumper in the pins on the box located on the left hand side of the car that bypasses the idle air control valve. I'll go back through my notes for when I set the base idle mixture on my car.

Nope! It was the 02 sensor "disconnect the stock O2 and leave it off. Then warm the car up on a decent 15 minute drive then let it come to idle and the idle AFR needs to be set at 14.0 to 14.2 AFR if it is not you need to turn the mixture screw located at the bottom side of the Air Meter. Turn it in (clockwise) to richen and counterclockwise to lean it. Adjust the screw till you hit the idle AFR target of 14.0 to 14.2 then proceed to driving it some while making note of the AFRs."

[kamaro]

I forgot to mention that mine is Euro specs, so no cat or o2 sensor is used in it.

[Big Dav]

I had the same problem on my 87 3.2. Idle mixtures were in the 11.8 range and the car always stunk of fuel. Turning the idle mixture screw out made no difference after a while and I think it was something like 8 turns out. Mixtures were very rich when driving but leaned out as revs got to near redline.

I checked my fuel pressure which was in spec and had my injectors cleaned and tested but the problem remained. Looking at my AFM showed that it had been tampered with and resealed with silicone before my ownership so I decided to take the plunge and open it up. It showed some markings on the spring and by adjusting one cog at a time and carefully monitoring AFR's I was able to fix the problem. It only took two teeth changes to tighten the spring to have a significant and positive change on mixtures. Now at full throttle it stays in the 12.5-12.8 zone going richer as it reaches redline. Idle mixtures can be set to 14.4 with the adjustment screw just over one turn out from full in. The car doesn't smell of fuel anymore and is super crisp and responsive to drive.

1/ Check Fuel pressure (too high will cause rich running)
2/ Have injectors serviced (leaking or stuck injector/s will cause rich running)
3/ If your AFM has been tampered with consider tightening the spring but be very careful and methodical with adjustments.

[911obgyn]

3.2 should have an 02 sensor, you need to jumper the plug on the left side of the engine compartment to center IAC and set CO and idle at the same time.
Make sure there are no vacuum leaks

[kamaro]

Originally Posted by Big Dav

I had the same problem on my 87 3.2. Idle mixtures were in the 11.8 range and the car always stunk of fuel. Turning the idle mixture screw out made no difference after a while and I think it was something like 8 turns out. Mixtures were very rich when driving but leaned out as revs got to near redline.

I checked my fuel pressure which was in spec and had my injectors cleaned and tested but the problem remained. Looking at my AFM showed that it had been tampered with and resealed with silicone before my ownership so I decided to take the plunge and open it up. It showed some markings on the spring and by adjusting one cog at a time and carefully monitoring AFR's I was able to fix the problem. It only took two teeth changes to tighten the spring to have a significant and positive change on mixtures. Now at full throttle it stays in the 12.5-12.8 zone going richer as it reaches redline. Idle mixtures can be set to 14.4 with the adjustment screw just over one turn out from full in. The car doesn't smell of fuel anymore and is super crisp and responsive to drive.

1/ Check Fuel pressure (too high will cause rich running)
2/ Have injectors serviced (leaking or stuck injector/s will cause rich running)
3/ If your AFM has been tampered with consider tightening the spring but be very careful and methodical with adjustments.

Thanks for the info, just to make sure that I got your modification, are you refering to the contact spring (showed in the following photo) that I need to bend it inside to make a stronger contact with the track?

[cabmandone]

Originally Posted by 911obgyn

3.2 should have an 02 sensor, you need to jumper the plug on the left side of the engine compartment to center IAC and set CO and idle at the same time.
Make sure there are no vacuum leaks

I thought so! I couldn't find that in my notes but it makes sense. As I understand it, the screw you're adjusting in or out on the AFM opens or close the flap in the AFM more or less allowing more or less air through at idle. The IACV would seem to fluctuate to allow more or less air as you adjust the screw on the AFM. So it would make sense that he IACV has to be in a constant position in order to adjust base idle mixture.

[Nick Triesch]

I understand that you can make a few adjustments in the air flo meter and idle and CO settings . But my mechanic who did my top end says you really are doing very little. He said that motronic really takes care of the few adjustments that we can make. When tuneup is complete and all vacuum leaks fixed, 3.2 should run fine without adjustments.

[Big Dav]

Originally Posted by kamaro

Thanks for the info, just to make sure that I got your modification, are you refering to the contact spring (showed in the following photo) that I need to bend it inside to make a stronger contact with the track?

No I didn't touch the contact arm which was fine and showed no error bench testing with a battery.

I'm talking about the big black cog wheel in the photo which is wound with a spring. Changing this has a dramatic effect on mixtures so do it carefully and only one tooth at a time and assess with your wideband O2. If you carefully lift the metal clip at the bottom and hold onto the cog you can adjust one way or the other. If you tighten it the air flap will move less with a certain amount of intake air and the motronic will add less fuel. Vice versa. If someone had tampered with it previously (like mine was) it might be the source of your issue. Make sure you check your mixtures at full throttle also by holding the car on the brakes in third gear at 4000, 4500, 5000, 5500 etc so you can make sure you're not too lean. I found that initially my super rich idle and low rpm running turned to alarmingly lean at high rpm. If you adjust the cog wheel a lot (5 teeth) you get nice mixtures down low but super rich up top. In the middle somwehere is the sweet spot with an almost linear AFR tending to slightly richer at redline which is good for safety.

This might not be your problem and I'm sure there are places in the USA that will check your AFM and set it back to stock configuration for you but I didn't have the option in Australia and it was a fun and relatively easy project to have a crack at myself.

[kamaro]

Originally Posted by Big Dav

I had the same problem on my 87 3.2. Idle mixtures were in the 11.8 range and the car always stunk of fuel. Turning the idle mixture screw out made no difference after a while and I think it was something like 8 turns out. Mixtures were very rich when driving but leaned out as revs got to near redline.

I checked my fuel pressure which was in spec and had my injectors cleaned and tested but the problem remained. Looking at my AFM showed that it had been tampered with and resealed with silicone before my ownership so I decided to take the plunge and open it up. It showed some markings on the spring and by adjusting one cog at a time and carefully monitoring AFR's I was able to fix the problem. It only took two teeth changes to tighten the spring to have a significant and positive change on mixtures. Now at full throttle it stays in the 12.5-12.8 zone going richer as it reaches redline. Idle mixtures can be set to 14.4 with the adjustment screw just over one turn out from full in. The car doesn't smell of fuel anymore and is super crisp and responsive to drive.

1/ Check Fuel pressure (too high will cause rich running)
2/ Have injectors serviced (leaking or stuck injector/s will cause rich running)
3/ If your AFM has been tampered with consider tightening the spring but be very careful and methodical with adjustments.

You nailed it. I also noticed that my AFM has been opened before, so I took it apart and tightened the spring by 2 teeth, now it idles right at 14.7 with about 4 turns out from fully closed. Thanks!!

[Big Dav]

Nice work! Just make sure you check your AFR mixtures out on the road at full throttle to ensure it's good all the way to redline.