O2 idle readings intermitent

[oldtimer02]

My AEM wideband started reading 17:1 at Idle intermittently!
I checked out the wide band per AEM directions: Spray carb cleaner on a rag, wrap rag around the probe, energize, wide band should go from 17 to rich & stay for a good probe, or 17 - rich- back to 17 for a bad probe.
My probe checked good!

Here is what I am seeing:
Startup: sometimes shows normal 14.7-15.4 then rev engine, back to idle - pegs 17! Sometimes 17 upon startup, Sometimes while driving goes to 17 at stopsign some times not.
It is always normal readings under cruise & boost!

So far: Checked the wide band, checked for leaks between the MAF & intake TB.

Next I'm going to swap the MAF from my friends '01 to see if it may be a bad MAF. Also I have an air cleaner that I clean & oil. It has been a long time since I did that maintenance though (2K miles) I will check for oil build up on the MAF when I switch them.

Any other thoughts?

[Gman7007]

Intermittent problems are sometimes caused by loose connections. I would check the AEM grounding wire.

Jose

[bogey]

Did you splice the oxygen sensor into existing wiring? If so, did you solder or crimp?

Solder connections on the stainless steel wires will fail. Always use crimp connectors.

[beatle]

How does the car run with it that lean? Do you notice a difference? One time when coasting to a light in neutral, I found the car began to stumble and choke. I looked down at my AFR and saw that it was 19! A quick tap of the throttle and the car came back. I'm guessing it was something TPS related.

Do you have a scanning tool that can monitor the fuel trims? If the ECU is pulling fuel, it will tell you. I notice a rhythmic pulling of fuel every 1-2 seconds when I start the car cold and drive away. I have no idea why it does this, but it goes away in a mile or so.

[oldtimer02]

So far I have swapped MAF, front o2 sensor. Found & fixed Exhaust leak at the cat.
Checked wiring to MAF.
I have a scangauge II TPS reads "0" at idle. Doesn't monitor fuel trim though. Every gauge reading on the scangauge is normal.
Idle is normal 850 RPM.
Unplugged my Piggy wiring adapter & plugged in direct to PCM.
My vac has always been low but I can't find any leaks.
Checked AEM ground - solid no problem there.
More suggestions???

No change noted!

[FormerDatsun510Man]

Does the car idle ok when it reads 17:1 or is there a miss. When an O2 sensor reports a lean condition it really means there is excess oxygen in the exhaust. This usually is because there isn't enough fuel to burn all of the O2, but also can happen when the fuel doesn't burn at all or if fresh enters the system. It can happen post MAF but pre cylinder, or post cylinder but pre O2 sensor. Just some general areas that I think the problem must lie within.

Bill

[peterc]

Hey oldtimer02, if your Scangauge has Xgauge, you can program it to read the fuel trims and O2 sensors.

Here is the link..

http://www.scangauge.com/support/pdfs/XGAUGE.pdf

[oldtimer02]

Bill,
the engine idles normally 830 -850 RPM no stumble or miss!

Thanks Peterc:
I'll check it out!

[oldtimer02]

Got it!
As usual it was something easy! The exhaust leak I thougt that I had fixed was still leaking. The FM mid pipe to down pipe flanges were mismatched by the use of too small diameter bolts allowing the leak. The correct dia. bolts w/self locking nuts & no mismatch! I guess I was careful to align everything when I originally installed the midpipe then when I found the bolts loose just tightened them the larger holes than bolt dia. is what got me.

[socal pat]

Good for you! It gives you an apreciation for how well bolted together a stock car is doesn't it? Being able to run for hundreds of thousands of miles without these niggling issues. But then again what fun would that be? Mine is running so well now that I'm glad to have one little issue that I think of as my "persian flaw". ;)