David Nycz

This is long sad story about my 2012 Equinox. This started at about 50,000 miles. When fully warmed up the engine would misfire at idle. It would misfire in gear or in neutral. If the engine speed was increased, the misfire would stop. When returned to idle, the misfire would begin again. The check engine light was on and displayed codes P0340 and P0300. A scanner was hooked up and it verified the random cylinder misfire. The misfire would shake the entire vehicle at idle. I replaced the following parts: Intake and Exhaust VVT solenoids, Intake cam sensor, spark plugs, ignition coils, upstream Oxygen sensor, downstream Oxygen sensor, and MAF sensor. This did not solve the problem. I took it to a GM dealership, and they found lose timing chains. They replaced all the timing chains. It worked for about two
weeks, and then started misfiring again. The GM dealer then re-flashed the PCM, cleaned the throttle body, and relearned the idle. This worked for about a month, then the misfire returned. The check engine light has not come on, but the misfire still occurs and shakes
the vehicle.I eventually replaced the PCM. The dealer flashed it and learned the keys. Again it worked for two or three weeks. Now it has about 70,000 miles. It misfires at idle in drive when fully warmed up, but it does not misfire in neutral or park.

I has also developed a new problem. If I pass with wide open throttle, the CEL starts flashing when I have completed the pass. The traction control light is also on and the dash says to service Stabilitrak. The engine never loses power, and it does not miss or hesitate under hard acceleration. After continuing down the road, all the warning lights go out and the dash is normal. The CEL does not stay on. Very strange.

I have just ordered a new throttle body assembly and a sensor for the exhaust cam position. That is about all that is left to change. Any help on this would be appreciated.

VzquzChris

did you ever figure out what the issue was? Im having the same issue on a 12' equinox as well and having no lock pin pointing the issue

David Nycz

The short answer is no, it still misfires at idle when it is fully warmed up. We took it back to the selling dealer in South Bend, Indiana. They had it for over two months, ( we were in no hurry ). They worked with GM technicians and ran several tests. They found a bad catalytic converter and replaced it for free. Apparently the catalytic converter is a known problem with this model. I assume the catalytic converter will fix the problem when passing at full throttle. However, we have not tested that yet. The dealer said it should be ok when passing. So far, it just misfires at idle, but does not stall or throw a CEL. If you put your foot on the gas and the brake and rev it slightly, the misfire goes away. We have a name for it now, we call it "Shaky" It will be traded in for a Honda CR-V this spring. Maybe the misfire is that great GM feeling?