So I am trying to track down a solution to an annoyance I have had with my 05 TB 4.2L SWB for the last 2 winters. I have an issue during winter (30-40F or below) that the RPMs fluctuate/stutter when coming to a stop or stop/go traffic at low speed after letting off the accelerator. For instance when I come to a stop as the vehicle is coming to a complete stop the RPMs jump up and down from roughly 900RPM-400RPM then the idle evens out to the correct speed (~620RPM) when I have completely stopped. Or if I am going through a drive thru or parking garage and give it a little gas the idle has a hard time coming to rest and will fall down like the truck wants to stall but immediately bounce back and idle correctly. This only happens in cold weather. In warmer weather the idle is perfectly fine when stopping and the truck drives great.
It's annoying and I can live with it during the winter but I would like some possible input. The throttle body is clean. AC Delco 41-103 plugs have around 20k on them if I would have to estimate. I do think that last winter I put in a bottle of Techron at 1/8th tank and it idled far better but next fill up the problem came back.
Fuel injectors? Loose intake manifold bolts? Motor mounts?
EDIT: P0420 code but I have a cheapo aftermarket catalytic converter
It's annoying and I can live with it during the winter but I would like some possible input. The throttle body is clean. AC Delco 41-103 plugs have around 20k on them if I would have to estimate. I do think that last winter I put in a bottle of Techron at 1/8th tank and it idled far better but next fill up the problem came back.
Fuel injectors? Loose intake manifold bolts? Motor mounts?
EDIT: P0420 code but I have a cheapo aftermarket catalytic converter