Rough idle when cold

I know what you guys are thinking, another question about this. However mine is different. I just had a code for the knock sensor. Replaced that and no other codes. Since replacing it when the truck is cold it will run very rough. Once it is in gear and you accelerate it has power, smooths out almost instantly. After that it is fine. The truck is a 94 Sub. with the 350 and 147K. I tried injector cleaner with no improvement. Could it be the EGR valve? I have not cleaned it yet.

I know what you guys are thinking, another question about this. However mine is different. I just had a code for the knock sensor. Replaced that and no other codes. Since replacing it when the truck is cold it will run very rough. Once it is in gear and you accelerate it has power, smooths out almost instantly. After that it is fine. The truck is a 94 Sub. with the 350 and 147K. I tried injector cleaner with no improvement. Could it be the EGR valve? I have not cleaned it yet.


Have U checked for vacum leaks.I checked eveything one my 2001 "sub". I found that it was a vacum leak at the intake manifold gasket. Take some carb cleaner at start up when cold and spray starting in front on one side and work your way back. If it starts to die or change idle thats what u have.
Replace intake manifold gasket.

Could be 101 things. maybe the ECT is reporting the wrong temp back to the ECM causing it run to rich or to lean.Maybe the o2's are getting tired and taking way to long to heat up,but not long enough to trigger a code yet.

I just replaced the o2 sensor along with a new cat. Its equipped with only one o2 sensor. I will check for vac. leaks around the manifold. I know on the drivers side in the middle of the manifold I have an oil leak so there may be a vac. leak there. I checked the vac. lines around the manifold and everything looks fine. Thanks guys!