I have a 2008 trailblazer with the 4.2L. It’s had a misfire on cylinder 1 for a while but only at idle, when you give it gas it goes away. I checked compression on all cylinders and they’re good. There is no oil on the plugs or the coil packs. I was driving the other day and it all of a sudden went into limp mode. The check engine light, the wrench light and the reduced power light came on. It has a fuel knock at idle pretty bad and will shut off when put into gear. But when I crank it a few minutes later it runs fine until I drive it for about ten minutes then all the lights come back on and starts knocking at idle again. Any help would be nice.

 

Do you have any dtc codes?

 

Yes it does. P0301 x2, P0171, P2135

 

P2135 is throttle position sensor, I'd look at that first as it could be causing the other misfire, and lean bank 1.

 

As a quick check, unplug the electrical connector going to the electronic fan clutch. If the reduced power light goes out and your engine functions normally again, then you have a bad fan clutch. Both the electronic throttle and the electronic fan clutch share the same 5 VDC reference voltage. If the fan clutch goes bad, it draws down the 5 VDC reference signal and the engine goes into limp mode and the reduced engine power light comes on.