Question2002 Silverado with a 5.3L V8 and 94k miles.
I have been having a rough idle occasionally after start-up. This happens only on cold mornings (less than 10-15 degrees F). After the motor warms, it runs fine. The CEL comes on occasionally as well, so I had the codes read. P0300, P0171, P0174, all appearing twice. I've been told a possible leak from the intake gaskets. Just curious what your diagnosis may be and how much cash I can expect to drop on each fix?
AnswerHey Eric,
I can't really offer you an exact diagnosis but I might be able to help with some of the basics without looking at the vehicle myself.
If we group all of the codes assuming the symptom is the cause of one problem it would break down like this: Those codes you gave are OBD2 Generic codes. Depending on the scan tool or code checker used they may be generalizing the problem. A TECH2 Scan tool is the most comprehensive piece of equipment you can use on a 2002 Silverado and will not only give the cylinders that are missfiring but how many times they missfire. If a cylinder 3 missfired 393024 times, it will tell you that.
P0300 Multiple cylinder missfire (missing on more than one cylinder)
P0171 Bank one system lean
P0174 Bank two system lean
The rough running you are experiencing is most likely a missfire when the air fuel mixture is at a point that spark needs to be good and strong. The oxygen sensors will not contribute to this until it is in closed loop and has to run for a few minutes to get up to temperature for the system to get into a feedback calculation.
Once thing you can do is make sure there is no air leaks before the Mass Air Flow sensor. This sensor measures the volume, temperature and density of the airflow going into the engine in a grams per second measurement. If there are any air leaks between the sensor and the engine non metered air will not be calculated into the pulse width (length of on time) of the fuel injectors causing a lean condition. Considering that you are getting lean codes as well you should really look for these air leaks. Make sure that there are no cracks in the tubes and the clamps are secure and tight.
Depending on what kind of plugs you are using you may be due for spark plugs. If they are original swap them out and monitor your driveability symptom again. Be sure to put dielectric grease on the leads to the coils.
Just because it is setting 02 codes does not mean you have a defective 02 sensor. If while you are driving along with a bad calculation fuel trim could be getting as high as 15% and not be able to accommodate air leaks.
The worse thing about the intakes on those vehicles is not air leaks but coolant leaks. If you are sucking coolant in the morning you are going to see a residue of hard whitish stuff on the plugs when you take them out.
Check for air leaks, replace the plugs and fuel filter and get back to me. I might be able to help you with the rest of the diagnosis if you have a DVOM and a code checker. I have seen deluxe generic code scanners on ebay for as little as 10 bucks. You can buy an excellent on from MAC tools that supports all data modes including CANdi for under 60 dollars. Considering that the most common GM code is a simple EVAPorative emissions code and guys charge upwards of 30-50 bucks to clear codes I would get one. I have a Tech2, Snapon MT2500 and MODIS, OTC 4000E, OTC Genisys, Vedis, 4000 enhanced and a laptop based one and I still carry the Mac Tools one around in my pocket for quick reference.
Wayne
Wayne
