AFM issue? How to remedy?

[CrossT]

I got my 86 3.2 back from the wrench for a few maintenance items including mix adjustment. He reported that while attempting to adjust the mix via the bypass screw on the AFM, he could not get any change in the mix. The reading is 4% and he was shooting for .8% or so I assume.

I have opened the AFM to retrace the wiper but that's it.

The DME is a rebuilt 24 pin replacement that the PO had put in and it is at the standard setting on the fuel quality switch. It is not 'chipped' [I looked].

Would it make sense to see this as a simple tightening of the spring in the AFM to lean out to the normal area of 1% or so? Then, have the wrench do a final adjustment. Is this a bad idea? He says that the O2 sensor is compensating for the base rich condition, so should I not mess with it?

thx
todd
86 coupe

[DW SD]

Some more info may be helpful.

Is the O2 sensor new?

Is the idle switch closed (so the DME knows it should be in idle mode)?

Steve Wong's website :www.911chips.com has a good overview of setting the base idle mixture. Knowing the process may be helpful in discussion with your wrench.

Doug

[Steve W]

Hopefully your wrench tried to adjust the mixture with the O2 sensor disconnected. If the idle CO is 4% that is very rich. I believe you are at a high elevation correct? - if so check for activation of the altitude sensor. I'd also check, fuel pressure regulator and pressure, head temp sensor, and bad or leaky fuel injectors.

[T77911S]

i changed the spring on a 280z a long time ago, ran great after that.
i would only do it as a last last last resort. the 280 had a LOT of miles on it. maybe i was compensating for something else wrong or maybe the high mileage?

[don911]

I had a similar issue mixture issue with my AFM once. However, my mixture was so bad the car would not run very well. I assume yours is running fine even with the rich mixture so this might not be the problem.

Anyway, mine turned out to be the contacts on the connector that goes into the afm. The connector was pushed in all the way but two of the actual contacts pushed back and were not making contact.
It's an easy check. Remove your connector and see if the contacts are all up to the edge of the connector. or pull the rubber boot back and make sure the contacts are in all the way.

Now, everytime I remove the connector, I pull back the rubber boot and make sure all the contacts are in all the way.

[CrossT]

Thanks guys

The car does run fine and it passed smog recently.

The O2 sensor is ~30K.

The idle position microswitch was tested [by me] a few years ago and it was good. I should test again. I can hear it engage - so I think that's good.

Good thought on the connector. I'll check that.

The elevation here is Tucson is about 2,500. I once found by altitude sensor wiring had been disconnected by moving the seat back and forth. So, I'll check that too. Thanks.

The wrench is exclusively a Porsche mech. He recently had the engine out and I had him check for vac leaks, and there were 'none'

Maybe I'll reconnect the brown wire on the DME harness [ ? ] since it is a CA car. Bad idea? I don't think I want to mess with the fuel quality switch.

So, I keep comong back to the AFM spring. The car has almost 190k on it so I suppose the spring could have stretched.

thanks again
todd
86 coupe