HELP O2 sensor again or is it? GRRR

[huntman58]

Hi ya all again
Okay I have been fighting this problem now for over a year on and off.
So far in the last month and half on my 1993 explorer I have done the fallowing after pulling codes
KOEO = 10 (pass) CM = 176 KOER = 111 (pass)
1) Replaced O2 sensors (both)
2) cleaned the MAF (for the umpteen time!)
3) checked all vac lines (all okay)
4) Replaced bad coil pack with acel unit (stock unit out of specs)
5) New plugs (auto lights double plats) #5 is burning oil others are normal.
6) Check plug wires no problems (all with in ohm specs)
7) Checked and tried to retighten intake bolts (all tight)
8) Checked for intake leaks (starting fluid was used and no leaks)
9) Cleaned and oiled K & N filter (filter is set on paper towels to wick any extra oil)

This is what happens I can drive all day at speed and never get a CEL as long as I do not do but very limited stop and go or idling. It has been this way for over a year. I changed the O2's out and problem went away for a week then back. This was a year ago. Changed O2's again a bit over a month ago and today got the CEL again with the same code 176 as I have always gotten. KOEO = 10 pass CM = 176 KOER = 111 pass
I get about 17 to 18 MPG as I have for years. I do have a K & N filter that is NOT OVER OILED and is still paper toweled as a safety stop gap to remove any extra oil in case before I install it. code comes only with idleing and warmed normal motor never when cold or at speed .

I over time have tried all of the above to take care of this and again to day I did items 2,3,7,8. All checked out okay. Cleared the pcm and did a test drive. High speed no cel. 15 minutes of stop and go with idling and CEL came on. Pulled over ran codes and got the 176 again. Got on the freeway and as always after about 2 to 5 minutes (3 to 6 miles or so) CEL turns off and will stay off tell I do lots of stop and go or ideal time.
I find this crazy as I just changed the A/C evap core and recharged the A/C. In doing that job there was a lot of idling and some high speed idle (1,500 rpm by the dash gage) and not a single CEL at all. I also did not get it with a lot of idle time and slow speed driving (Idle speed only no pedal at all) here were I live. This also was a lot of stop and go in an orchard so dirty and dusty also again no CEL at all. Seams like I have to have driven at speed first before the CEl will come on as it has never came on with me just idleing .All this driving has been in the last month or so and all with no CEL tell now. I am planning to look at the battery leads and check clean as needed. I do know that #5 spark plug is burning oil when I changed plugs it was fully oil fouled and the rest were normal. Pulled it and rechecked it after about 100 miles and it is showing a little oil burn still (Possible bad valve guide or seal). Motor dose leak some oil at the timing cover but that is all no valve cover leaks ever and no head problems at all. Truck has about 210,500 miles.

What am I missing? Could it be the PCM or just a bad MAF? I checked the FPR and no gas in the vac line but I do not have a gage to test the PSI or leak down.
I am at a lose any more with this. In reading post on this I found many good ideas but no real I found it ideas. But I need help as this is just driving me NUTS!
sorry so long but wanted to give the pros all the details.

 

[MrShorty]

Since the problem isn't showing up in the KOER test, and the CEL isn't on constantly, that suggests to me that whatever is causing the CM 176 is intermittent (only shows up under certain specific conditions). This is likely to make it difficult to diagnose.

You mentioned that plug #5 is having fouling issues. Fouling on plug #5 is often associated with loose lower intake manifold bolts. A misfire can, in theory anyway, trigger a lean code, so possibly the lean code is related to the potential misfires/incomplete burn on #5. I would check the lower intake bolts and make sure they are tight. Also note that a leaky gasket here can let coolant into the cylinders, and coolant can poison O2 sensors.+

 

[huntman58]

I have wondered about the # 5 cylinder and it's burning a small bit of oil. My thought would be it would be a bit rich not lean thou am I wrong in that thinking? I know the intake is nice and tight and showed no leaks when I sprayed around it. I went a head and tried to tighten things up and well they were tight already. No coolant loses at all. I believe the oil is coming from a possible valve seal or guild problem just on that on cylinder as it is the only one showing any thing not normal but after almost 210,000 miles it has the right to burn some no matter how bad I hate it LOL.
I did check the volts at the MAF and there in spec also the ohms at the IAC valve. Also cleaned it and the MAF even thou they were clean. Wiped the CM codes and cleaned the battery post and wires then retightened them just to make sure again there not an issue. But being like you said a hit or miss deal it is frustrating and a major PITA to find and fix grrr!