Runs bad at an idle but not all the time

Tiny
BBZ
  • MEMBER
  • 2005 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 112,000 MILES
I checked for codes cleared them and the same ones came back. The three I have is po131 po171 and po300. The exhaust is sooty. I have not checked the fuel pressure regulator yet nor have I checked fuel pressure. I also have not pulled the plugs. I did put plugs in the truck about 3,000 miles ago they had a good color to them then. Not full of deposits either.I have cleaned the mass air flow sensor.
Do you
have the same problem?
Yes
No
Friday, May 9th, 2014 AT 7:06 PM

8 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
P0171 - System too Lean (Bank 1)

P0131 - Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 1)

P0300 - Random/Multiple Cylinder Misfire Detected

Okay, the 171 leads me to believe there is a vacuum leak. Have you checked for that? The idea that you have a po300 can be the result of both other codes. Have you checked the wiring to B1S1? Have you checked the sensor itself? Do you have access to a scanner that can provide live readings of how the sensors are reacting?
Was this
answer
helpful?
Yes
No
Friday, May 9th, 2014 AT 7:18 PM
Tiny
BBZ
  • MEMBER
Looked at vacuum lines, used carb spray on lines and on intake manifold. Found no leaks. Someone said the intake gaskets are prone to leakage after about 100,000- 150,000 miles. They said the gaskets are an rubber o-ring type and they loose their shape and will cause a vacuum leak that will not identify with carb spray. I checked fuel pressure, has 55lbs. The pressure increases like it should when the throttle is snapped. I found no vacuum hose and no fuel pressure regulator on the fuel rails. I checked both rails a few times but found no regulator. Fuel comes in on the left side, there is a crossover tube going to the right side. On the right side is the schrader valve for checking pressure. But that is all except for each individual outlets for the injectors. Thanks for your help.
Was this
answer
helpful?
Yes
No
Saturday, May 10th, 2014 AT 5:05 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
They are pron to have problems. I've found many with coolant leaks. If the fuel pressure is good, then the regulator (that could be on the pump) is working.

You know, about a week ago, I ran into a problem with a Chevy van that ran bad at times at an idle. It would start running bad at times off an idle, but the idle was the worst. It would actually die. Other times it ran perfect. What I found was the coolant temp switch was bad and sending a bad signal (only at times) to the computer. As a result, the computer would run in a closed loop and dump fuel because the sensor told it the coolant temp was -40 degrees F. It was a a 20 dollar part and once replaced, it ran perfect. You are showing a lean mixture, but the coolant sensor could do the opposite telling the computer it is hot and lean the fuel mixture. It's just a thought. And yes, I was getting a PO300 from the vehicle. The O2 sensor codes you get COULD be the result of this type of issue.

The only way I was able to find the problem was to scan the computer with an active scanner that showed me what the ECM was seeing. Do you have access to a scanner like that that you could check such things?
Was this
answer
helpful?
Yes
No
Saturday, May 10th, 2014 AT 6:33 PM
Tiny
BBZ
  • MEMBER
Monday the 12th of May I will be hooking the truck up to scan tool. All I had before was a code reader. I will also be checking the o2 sensors. What has me puzzled is the black soot on the inside of my exhaust pipe and on the body. When I go to pass someone and I give it full throttle I also get the black soot smoke. That is why I thought it might be running rich instead of lean. But I might be mistaken. I might have the two conditions mixed up in my head. I'll get back with you Monday and let you know what I found and hopefully solve the problem. Thanks again Bob
Was this
answer
helpful?
Yes
No
Saturday, May 10th, 2014 AT 8:01 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Bob:
The black smoke / soot does sound like it is running rich. Make sure to check the temp sensor too.
Was this
answer
helpful?
Yes
No
Sunday, May 11th, 2014 AT 12:51 PM
Tiny
BBZ
  • MEMBER
I have to apologize for not getting back to you two sooner. I replaced the coolant temp sensor, it did not help. Plugged the truck into a scan tool, 02 sensor B1 S1 was reading of the chart compared to the other three. I am guessing the sensor shorted out. I disconnected the sensor the truck ran fine. It did take awhile to clear out the exhaust from all the extra fuel. Checked the codes again had one for the sensor being disconnected. Will be changing the sensor over when it gets in. Bob
Was this
answer
helpful?
Yes
No
Saturday, May 17th, 2014 AT 11:06 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Let me know if that takes care of the problem. That could be the entire problem.
Was this
answer
helpful?
Yes
No
Sunday, May 18th, 2014 AT 7:57 PM
Tiny
BBZ
  • MEMBER
Popped in a new 02 sensor (sensor1 bank1) today. Cleared codes, checked to see if any new codes, no new codes. Sensor is working like it should. It is reading about the same as the others. The truck is back to running normal again. Thanks again, Bob
Was this
answer
helpful?
Yes
No
Wednesday, May 21st, 2014 AT 7:50 PM

Please login or register to post a reply.

Related Engine Runs Rough Content

Recommended Guides