It does what? doesn't sound like a very good way to stop engine damage to me.

__________________
Signarape!

The only time you'll get a cel for the AFM on a 99-00 is if it goes open circuit (or it's unplugged)....Which is very, very rare.

The usual mode of failure is for the voltage to fix somewhere between 1-4 volts and stay there regardless of actual airflow.

This confuses the ecu at idle (the ecu sees the rpm and the tps (<10%) at there idle values, but the airflow is mid scale between 1-5 volts).

The ecu then ignores the tps and the iac opens fully to it's off idle position -- causing the RPMs rise.

The ecu goes woah!! RPM too high--- I'm meant to be at idle and it shuts the iac to it's minimum position -- The rpms plummet....ecu goes huh? high air flow and opens the iac again.....It's a continuous loop.

^^This is when most people first notice an 'issue'.^^

Then it usually throw a TPS or IAC out of range CEL....NOTHING for the AFM which has been dead the whole time.

Every 99-00 AFM that I've seen fail has had the same symptoms, Hunting Idle, the scary not wanting to stop thing and either a TPS or IAC cel (or both).

The AFM is the only load sensor for the factory system, the car may idle with the afm unplugged but that's because the ecu is closed loop at idle. if the ecu 'see's' an afm output above its idle voltage range the ecu loses it's mind, it will 'believe' the afm over the tps.

This is why 99-00 cars with a dead AFM will keep pulling as you try to slow to a stop, the ecu reads the afm signal and keeps the iac fully open (off idle position) whilst fueling for the load the AFM is telling it.... Scary the first time it happens! lol!

As far as working out an actual load from the TPS and RPM alone, it can't be done these are turbo cars and the manifold pressure is irrelevant to both of those inputs....The TPS is used for Idle confirmation & throttle enrichment only.

This is why 99-00 GC8's go BOOM with a dead or dying AFM, ecu see's the fixed or erroneous load, the engine comes on boost and it goes lean...Ping, ping = dok! dok!

As far as richening the mixture, the factory narrow band O2 sensor is only used for cruise AFR's/ cat converter effeciency & nothing more.

The 99-00 AFM's are a well known engine killing weakness, even Subaru themselves will tell you that you should carry a sapre in the glove box for when it fails, not if it fails.

MRT recommend to replace them every 12 months regardless of km traveled, cheaper than $8k for a rebuild.

Feel free to show me where I'm mistaken

__________________
[CENTER][SIGPIC][/SIGPIC][/CENTER]
[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]

Well guys I put the new AFM in today seems to have fixed the issue with the idle, sits on about 800revs so im assuming that's about normal. Going to start it up again in about an hours time see if it does anything strange after it settles.

But thanks to all your help guys and Chris for the part, ill let ya know if anything plays up but so far all good.

Cheers
Danny.

Wouldn't cutting fuel at high rpm and load kill the motor?

That's what I was thinking.

__________________
Signarape!

Did seem like it was over fueling slightly but soon as I out it in took about 5mins for it to stop now no fuel smell anymore.

Do an ecu reset (Search here there's a sticky somewhere). That will allow the ecu to relearn the timing & forget any bad habits its stored & clear any cel codes.

__________________
[CENTER][SIGPIC][/SIGPIC][/CENTER]
[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]

no probs danny, glad it fixed your problem $80 well spent