rich or lean at idle?
 

I have a S5 TII and was wondering if it should run rich or lean at idle? It seems to vary from time to time but the idle is noticeably smoother when it's rich. What would cause the a/f ratio at idle to vary? Thanks.

What specific AFR's determines rich or lean when you say that? I know when my friend (guitarjunkie on the boards) and I were tuning with his wideband, my car wouldn't want to idle at anything leaner than 13.5:1 AFR.

I would say to run it as lean as possible within a safe margin. No reason to waste all that extra gas. Then again, that's my theory.

Personal experiece says they run smoother at around 13 to 1 afr. When run leaner they go poo poo, puff puff, all the time at idle. I've no idea why yours changes at idle...from lean to rich or whatever it is doing, all by itself. Could be several things that I'm sure someone else will pipe in with.

I'm not sure what afr's I'm running at idle. I'm just going by a narrowband a/f guage and SAFC. I have the O2 sensor hooked up to the SAFC so I can get a voltage reading from the sensor check screen. When the voltage is at 0, it idles as Hailers described and the engine just feels more shakey. Other times it'll read at .8xx volts and idle really smooth. I just find it odd that it's not constant and would like to fix whatever the problem could be.

For some ungodly reason, my car seems to like 12.5 idle mixtures.

ITs a fuel hogging bitch....

ttt

.8v is about what you'll see on a stock setup. Even with all of my recent "lean during cruise problems", she always went back to .8 at idle, so you've got yourself one funky problem there. Check the variable resistor input at the ECU, maybe you have an intermittent snafu at the resistor out on the right strut tower causing her to go lean at idle. Either that, or you have a nice vac leak that may be intermittent...

If you see .8v at idle.....you've got problems if you still have your airpump and acv and solenoids working. A stock RX at idle should see zippity doo dah at idle. Maybe .1 or .2, certainly not .8. That .8v indicates a lack of air getting to the exaust ports at idle ...from the airpump.

No airpump or acv on the car anymore. Should the car constantly be idleing around .8 without them? Looks like I'll be checking for vacuum leaks and going from there. Thanks for all the input so far.

Oops, my bad...It's been so long since I've had port air, I probably never took O2 sensor readings for comparison when that system was operational. That .8v I'm refering to is normal WITHOUT the port air system functioning (i.e. no ACV). Good for you, Hailers, you busted me :)