I've been having intermittent issues with my truck idling. Only after it has sat all night or if I'm waiting for the train, which can take 30+min. The truck starts fine and drives fine but if I let it warmup for a couple minutes without touching the throttle, it develops a VERY rough idle and sounds like it's way off on the timing or only running 3 cylinders... If I shut it down and cycle the ecm, it starts right up and no issues. I hooked up my Bluepoint Scan tool and found some interesting data points. I can't seem to find what these mean so if anyone here could throw me a knowledge bone, that'd be awesome. All of the other tests showed within limits and I noticed the O2 monitors were a little wacky as well.

Test ID- $11 value=11
min=44 FAIL

Test ID- $19 value=2870
max=1580 FAIL

Test ID- $1A value=3771
max=1580 FAIL

o2 S11(v) -0.120
SHRTFT11- 0.0

o2 S12)v) -0.220
SHRTFT12 -99.2

 

What I am seeing there is short term fuel trim on bank 2 is pulling fuel in a big way. Disconnect your front O2 sensors. (both of them, yes, they will set codes.) Drive the truck. No more problem? Replace both sensors.

 

The thing that is throwing me off is that the value stays around or at 99.2 even when the truck is running good. Fuel mileage is around 15mpg which I remember my 95 got around 18mpg. Both being 4x4 but this is a swb 5.9 and the other was a lwb 5.2

 

Well, I think the *max* value there is going to be -128.... so, the PCM is pulling a LOT of fuel from that bank. Most noticeable at idle I would imagine, with a serious lean-burn miss.

Try disconnecting the sensors. See if it runs any better.

 

That seems to have done the trick. CEL of course but ran just fine. I'm going to test it again first thing in the a.m. to see if it acts up. Can I plug one in and see if it's one or the other? They both look relatively new but who knows with a used truck.

 

Best bet would be to just replace them both...... They both live in the same environment, after all. But, looking at the numbers, Bank 2 is the one that I believe is problematic. Should be passenger side. Try plugging the drivers side back in, see what happens.

 

Wait... I only have 2 o2 sensors. Before and after cat. No left and right, one is after the y pipe and the other is after the single cat. Is this a normal setup or is something else going on?

 

No, yours is normal. California emissions have 3 sensors, left bank, right bank, and after cat, I think.
Your read out (at least the bottom part) is short term fuel trim bank 1-sensor 1, and bank 1- sensor 2... which basically means front sensor and rear sensor.

 

Ignore me quoting this. Dunce moment

 

Crap. I was thinkin' Cali Emissions. Frankie is correct. Though I am curious why the rear O2 sensor seems to be wanting to trim fuel...... (That is a -99, right? Not just a dash?)