High idle after exhaust changes?

[CorsePerVita]

Did a fabspeed muffler bypass on my 911. Now after the car is warm, the idle is normal. But COLD high idle is sometimes higher than it was. Sometimes 2300rpm. The odd thing is it starts off normal high idle. 1800ish.. gradually climbs to 2300rpm. By the time the car is normally warmed up it goes back down to normal.

Car runs fine. Runs smooth. Everything seems fine... but the high idle is weird to me.

Obviously if I turn down the idle then when the car is warm it's gonna bugger it up. So why is the COLD high idle so freaking high sometimes? It doesn't start that way though.. very strange to me.

BTW: My sound ended up being alt bearing earlier and got that fixed so she's back to happiness (aside from this lol)

[Reiver]

When you put the cat bypass pre muffler on you changed the breathing on your car, better flow with an already stock lean CO. I'd check your CO numbers now as you are prob running too lean without the cat (higher idle) and need the CO fattened up a bit to 2.5 to 3. Your CO sensor can compensate some on the warm/hot motor.
What fabspeed system are you running?

[Bob Kontak]

Originally Posted by Reiver

What fabspeed system are you running?

CorsePerVita said he put on a muffler bypass.

If I recall the Fabspeed muffler bypass is an angled pipe that comes off the cat/cat bypass and discharges exhaust without the muffler.

Reiver, I think your original thoughts are valid, just that the muffler bypass reduces back pressure even more than a cat bypass or Euro pre muffler setup.

[1985RedTarga]

I have the same Fabspeed set up on my 85 and didn't notice anything changing. Perhaps my computer adjusts for it?