Rough idle; running lean (p0300, p0171)

samy1969

New Member
So I got the P0300 and P0171 codes on my 2004 Envoy XUV 5.3L v8 130k.

I've read about 100+ posts on the TV site and while wandering off into a temp actuator issue, I saw a reference to this gmtnation site. It looks like more people are on here, or at least more people may be able to respond, so I'm posting my issue here in hopes I can get some help.

P0300 - Engine Misfire Detected
P0171 - Fuel Trim System Lean Bank 1
The exhaust smells bad, not like sulfur but like regular exhaust that's choking. There was a FAINT trace of white smoke coming out, but I emphasize faint because this looks nromal to me.

Here's what I've done:
- 3 years ago, about 100,000 miles, replaced the fuel filter
- oil changes every 5-7k
- air filters every time they're dirty (inspected during oil change)
- 6/22/2013, checked air hose from filter to throttle body, no cracks found
- 6/22/2013, inspected throttle body (didn't remove it), looked pretty clean but didn't clean it
- 6/22/2013, replaced the spark plugs with AC Delco Irridiums (part 41-110 from Advanced Auto Parts); broke one wire along the way, replaced only that 1 wire
- 6/23/2013, ended up cleaning the throttle body with throttle body cleaner (used about half of the can)
- 6/23/2013, inspected MAF and screen, everything looked to be very clean
- 6/23/2013, searched for the egr valve, couldn't find it (it seems this engine doesn't have one, much to the surprise of me and a couple of friends)

Here's the weird thing on the plugs: In cylinders 1,3,5,7, all 4 of the plugs (for effect: ALL FOUR OF THE PLUGS) were black and seemed slightly damp. In cylinders 2,4,6,8, all 4 of the plugs were white and chalky. See picture of the plugs.
View attachment 29104

Also, I captured some data from my OBD Scanner. I didn't have paper and pen handy, but I used my phone and rapidly took pictures for about 15 seconds. Here are the results of the O2 sensors and the fuel trims.
volts volts volts volts % %
O2S11 O2S12 O2S21 O2S22 FTRM11 FTRM21
0.300 1.005 0.050 0.760 50.8 2.3
0.325 1.015 0.070 0.465 48.4 6.3
0.230 1.015 0.920 0.835 48.4 2.3
0.295 1.020 0.885 0.840 48.4 0.0
0.365 1.015 0.080 0.855 50.0 0.8
0.345 1.015 0.820 0.820 46.9 -2.3
0.320 1.005 0.065 0.230 47.7 0.0
0.280 1.010 0.905 0.110 48.4 -0.8
0.330 1.015 0.100 0.565 49.2 0.8
0.165 1.020 0.910 0.815 49.2 -3.1
0.375 1.015 0.060 0.080 48.4 -2.3
0.295 1.010 0.855 0.050 48.4 -0.8

Sensors 12 and 22 vary wildly, sensor 11 has some variability but not much, and sensor 12 seems stable.

Looking at the fuel trim, 21 has so much volatility in it but 11 reamins relatively stable. (admittedly, I need to read up on fuel trims to see what these are)

I understand I'll need to replace the O2 sensors at some point, but I was hoping this data could point to a particular one since replacing all 4 will cost me about $280 in parts alone. Replacing the MAF sensor will also set me back a decent amount (I think about $75), and right now I don't have much extra to sink into the car. Another month, I'll be better off, but I need to fix my car sooner than later.

Hopefully someone can help...

Sam
 

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BRomanJr

Well-Known Member
Any P030x code and/or blinking SES light can be bad for the cat(s).

The O2S21 (Bank 2 front sensor) sensor looks ok, but may still be sluggish (lazy), the O2S22 is probably ok.
The O2S11 (Bank 1 front sensor) is not working or there is an air/fuel problem.
Start by replacing both FRONT O2 sensors, they are a pain to do. These are a wear item and anything over 100k is an acceptable lifespan. The rear sensors should only be replaced when a code leads to them as a problem.

The spark plug wires seemed very fragile to me and even though I was careful, damaged at least half of them during removal (160k miles). based on this and your trucks mileage/age, I would replace them all.

Since all of the plugs on the drivers side were fouled it's possible you have the defective drivers side valve cover and it should be replaced with a new GM part.
Do you use a lot of oil between changes?

The Throttle Body on the V8 engines is not susceptible to getting dirty and frequent cleaning is not needed.


Let us know what you find along the way.
 
OP
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S

samy1969

New Member
Glad you mentioned the blinking SES light. Mine was blinking and I pulled over and turned off the engine. Left off for 5 minutes, restarted, then drove again. A few minutes later, it started blinking again. This happens each time I drive the car now, which isn't too often since I may damage something like the cat.

On the oil usage, I check the oil tank EVERY fill-up and it's almost always full. The only time I'd have to add any oil was during a road trip and I needed about 1/4 of a quart. But the car is driven mostly in the city (90% of the time) and I never have to add oil.

I spoke to a good friend last night and he mentioned to look at the power wire going to the driver's side fuel rail. He said it's possible the fuel rail isn't getting power, thus resulting in that whole side of the engine not firing correctly.

For the wires, they all seemed pretty good. I am planning on testing the power out of each coil to ensure the coils are firing. If they are good, I'll test each wire by removing them one at a time to see if there's an even rougher idle.

Also, to add to the initial problem, the rough idle only starts when the engine has been run. When it's cold, the engine runs great...no misses. I can start the car and let it idle for a long time (an hour even) and it'll never miss. But after I start driving it, about 10-15 minutes later it starts to rough idle and the SES light comes on. What's odd is that when I accelerate, the power seems completely fine. It's when I'm running or when I'm at a stop that the engine seems to miss. I guess it's possible there's still a misfire even when I'm accelerating, but I don't feel it if there is.
 

BRomanJr

Well-Known Member
samy1969 said:
Glad you mentioned the blinking SES light. Mine was blinking and I pulled over and turned off the engine. Left off for 5 minutes, restarted, then drove again. A few minutes later, it started blinking again. This happens each time I drive the car now, which isn't too often since I may damage something like the cat.

On the oil usage, I check the oil tank EVERY fill-up and it's almost always full. The only time I'd have to add any oil was during a road trip and I needed about 1/4 of a quart. But the car is driven mostly in the city (90% of the time) and I never have to add oil.

I spoke to a good friend last night and he mentioned to look at the power wire going to the driver's side fuel rail. He said it's possible the fuel rail isn't getting power, thus resulting in that whole side of the engine not firing correctly.

For the wires, they all seemed pretty good. I am planning on testing the power out of each coil to ensure the coils are firing. If they are good, I'll test each wire by removing them one at a time to see if there's an even rougher idle.

Also, to add to the initial problem, the rough idle only starts when the engine has been run. When it's cold, the engine runs great...no misses. I can start the car and let it idle for a long time (an hour even) and it'll never miss. But after I start driving it, about 10-15 minutes later it starts to rough idle and the SES light comes on. What's odd is that when I accelerate, the power seems completely fine. It's when I'm running or when I'm at a stop that the engine seems to miss. I guess it's possible there's still a misfire even when I'm accelerating, but I don't feel it if there is.
Change both front O2 sensors (AC Delco or Delphi only) this is the most likely problem.
 
OP
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samy1969

New Member
I first checked the power to the fuel rail and it looked to be in working order. I didn't use my voltmeter because I could hear the fuel being pushed through when the ignition was turned on.

I then replaced the pre-cat O2 sensor and decided to give it a test-go. I unhooked the battery and held the wires together for 30 seconds to clear the memory. Fired up the car and as expected, the idle was fine. But the SES light was on, so I learned that shorting the wiring may require longer than 30 seconds the clear the codes. I used my scanner and cleared the SES light. Drove it for about 2 hours around the neighborhood, things were working fine. I then decided to drive it to the office the next day. About 10 minutes into the drive, lo and behold SES light came back on. But the engine was still running fine, meaning no misfiring that I could feel. When I got to the office, I read the codes and had all new ones:
- P0133
- P1133
- P1134

But, the P0300 and P0171 were gone! So I consider this progress. Did some research on these new codes and decided I wasn't in danger of ruining the engine or killing someone. Decided I needed to re-check the wiring harness and posisbly re-install that O2 sensor. Drove home that day, SES still on, but engine running fine, and then it rained all night and all next day. Then more rain the rest of the week. Then I had to fly out to Boston for the 4th of July weekend. Figured I'd go ahead and drive the car to the airport, and on the way to the airport, the SES light went off!!!

I haven't been home yet, but I'm hoping this means that it took a few cycles for the computer to learn the new O2 sensor. Fingers are crossed...

Sam
 

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