I own a 1999 Tahoe 5.7 L 4x4. Recently, it has been starting to idle rough after it is first started. Any idea what could be causing this issue?

Smoke has also been coming out of the exhaust as well when idling and accelerating. The smoke issue does not happen every time I drive the car, but it happens sporadically. It is white smoke, which I know isnt good. The car has been running fine besides the rough idle, so I really dont know what could be causing the issue. I looked it up online and it said that it could possibly be coolant mixing with fuel, but my coolant level has not gone down. Could it be related to anything having to do with the Catalytic converter? In August, I got a check engine light and when we checked it, the code was related to the catalytic converter.

I have owned 3 different Chevys with 5.7s and I've never encountered issues like these.

 

check your intake gasket it will leak very little coolant that can get in your cylinders and cause the smoke and misfire. thats where i would start.

 

check your cats by going under the vehicle and smacking the cat if you hear a rattle then you got a bad cat.

 

would a bad cat be the cause of either or both of these problems? I know that there is something wrong with the cat since I had the code read. I dont know the exact code, but it relates to a bad cat.

 

I'm not sure but I don't believe the cat can do it. I would try and find a set of cats if yours is like mine and replace them cause the cat can cause the rough idle.

 

alright well at least replacing the cat will solve one of the problems. I am having my mechanic look at it tomorrow and I will let you all know what the cause of the various problems are so that others who may experience the same issues can look at this thread for reference

 

You may have either an intake manifold leak or a blown head gasket. The intake has to come off regardless once that is off you should be able to see if the intake gasket is cracked or blown. It is better to check with an automotive shop.

 

I have a 99 Tahoe having the same issue. Rough fluctuating idle and just got a mechanic to replace head gaskets because loosing coolant and fluctuating temp gauge and the idle. turned out needed two new heads and it still has the same idle fluctuating idle? Anyone have this issue and able to fix it? I’ve replaced idle control valve and egr. And my Tahoe doesn’t have Catalytic converters only the factory muffler.