MAF and O2 sensor levels?

I've been trying to track down the cause of my unstable / floating idle issue and finally received the ElmScan tool that I ordered through DigiMoto at the beginning of the year. Pretty nifty little toy. Anyway, I plugged it into my car while it was idling and, sure enough, the RPM at idle jumps around 800 RPM by +-30 RPM or so. The realtime graph of engine speed looks like a mild wave centered around 800 RPM. Looking at the O2 sensors, I've noticed that each bank appears to have 2 O2 sensors. The first O2 sensor per bank seems to fluctuate at a consistent period between about 0.1 and 0.65 (volts?). The second O2 sensor per bank seems to be more consistent; both hover between 7.05-7.25 (volts?). The MAF readout seems to hover around 6 (gm/s?), but does consistently vary between 5.75 and 6.25 and sometimes drops to 5.25 or jumps to 6.75. This is while the car is just sitting there at idle, not touching the throttle. I *think*, although I'm not sure I can correlate this just yet, that I have seen spikes in the MAF level associated with spikes in the engine RPM. It's difficult to tell as the precision of the graphs output by the DigiMoto software doesn't seem to be all that great for some reason. Anyway, are these readings normal? Do they indicate anything like a failing or dirty MAF / O2 sensor? I've also noticed that the short-term fuel trim figures for each bank fluctuate a lot but the long-term trim figures are pretty consistent: 0 for the first bank and I think -1 for the second bank. Does that maybe indicate something else to look at? I've got no reference for what these numbers should look like and it feels like I'm fumbling around in the dark. I'd invest in a factory workshop manual, but it seems like a waste as I don't have the ability to do any major work on the car (no garage space / tools) anyway. Among other helpful suggestions, 1999Porsche911 mentioned that I should try cleaning the throttle body. Since I've got no reference, what do I need to do to get at the throttle body and / or the MAF to clean them? Do I need to take off the airbox or is there an easier way to get to them? Thanks for any help you guys can provide; I'd like to get this problem licked as soon as I can and get back to enjoying the car!

Although your idle may be a little higher than the 700 rpm for a stock engine, the fluctuation of +- 30 rpm is well within the normal range and I would not describe you as having a hunting idle. O2 sensors (first) are doing what they are designed to do, but I think you may have written down the incorrect values of the second O2 sensors. These have a range from .01 volts to about 1 volts and should be more constant that the first sensors. At idle they may read only .08 volts or they may read higher, but at WOT (any gear) they should read at least .85 volts unless the engine is running lean. Your MAF reading are well within range also and that will vary with engine speed. MAF readings will always be higher when the engine is cold. Fuel trim is fiine. From what you are showing us, all looks to be ok. Are you experiencing an engine problem, CEL, etc? If you are concerned with the idle going up and down 30 rpm or so, don't be. and get out and enjoy the car. Turn off the air conditioner and see what the idle is then. Throttle body can be easily cleaned using spray carb cleaner sprayed directly into the throttlebody after removing the intake tube that is connected to it. Open the butterfly valve in the body and spray the cleaner on the parts to remove any built up carbon. Reassemble and start then engine which may run a little rough and smoke a bit until the cleaner is blown out of the engine.

1999 Porsche 911 - Good...Sound, advice. I too, had what I thought was a hunting idle. Then I took it out and ran it through a series of switchbacks and winding mountain roads. After two hours of hard driving everything seemed to settle down. The idle got smoother and the engine actually seemed a bit more responsive. I guess cleaning the carbon out of it (one way or another) once in a while is good for not only the driver but the car too!

I'm not experiencing a CEL. The engine does run a bit rough at idle somtimes -- feels like a mild thumping in the seat Strangely, the idle RPM is more stable when it feels like that. If it was just a slight tremor that came and went every 30 seconds or something I wouldn't care. But this is quite noticable and distracting when I'm sitting at idle. I'll see the tach needle constantly float around (around 2-3x the width of the marks on the tach -- between 760 and 830 according to ElmScan) and there is an obvious change in engine note / speed as this is happening. I also think this is happening up to around 2000 rpm when I try to give it constant gas in neutral, but that could be due to slight variations in my foot position. Sometimes it's smoother / pretty constant when stopping after a hard run (still hovers at 800 rpm with a bit of a fluctuation but barely noticable -- within maybe 0.5x the mark widths on the tach -- this I would consider normal). However, after a minute or so it falls back into this obvious floating behavior. I didn't notice this on other 911's I was looking at, and I didn't notice it on a coworker's 911 when I was consciously looking for it (after I had detected it on my car). I also didn't notice this on my dearly departed Audi. In fact, I'm not sure I've noticed this kind of thing with any other motor vehicle. So I've got a hard time believing this is normal for the engine. What would cause the engine to idle 100 RPM above stock? BTW, you were right about the secondary O2 sensors -- they seem to hover around 0.65-0.7 v. And with the A/C off, the idle hovers around 750 rpm but still exhibits the same amount of float (between about 720 and 780). I apologize if I'm not being all that cool about this. I'm worried about my baby and I want to make sure she's in good health. Again, thank you for your comments / suggestions!

How many miles on the plugs? Many car's throttle body parts have a slick plastic coating inside. I'd avoid carburetor cleaner, It will dissolve plastic. I think with the engine warmed up the short term fuel trim at idle should stay at +/_ 5%. When the mass air sensor went out on my turbo the long term fuel trim went as high as 21%.

The car has about 24k miles on it and I bought it at 17k. So I'd assume it has the original plugs since they're first changed at 30k, right? It might be worth changing them, but this behavior has been there since I picked up the car. The long-term fuel trim looks to be good (0-1% on both banks). I'll have to check the short-term fuel trim again, but IIRC that was bouncing around more than 5% at idle. I wonder if this is an indication of anything. I suppose this is kinda silly as I really don't know how the engine should be operating. I guess I'm going to have to take it by a local shop and get their opinion on it as well.

If you are absolutely positive there is not a small vacuum leak, I would guess that is its either the idle control valve. If you haven't cleaned the ICV, remove it and spray it with carb cleaner. Take note wheather the window in it is able to move smoothly. Try tapping the ICV when the engine is running and note any change in idle You can also take a hair dryer and warm up the ICV when the engine is running and se if there is a change in smothness. You can get a new one from Autozone.