vva causing a rough idle?

check and see if your wastgate is working properly to. usally when a vva sticks you will get white smoke when it misses like that,raw fuel escaping when it holds the valve open. but vva's are a tempermental thing.

 

I just recently had work done on the vva's on cylinder 3 and 4 on an mxs c15 cat. I was getting an intermittent check light that scanned as low voltage to the solenoid on the vva. The parts were 1000 bucks from cat and was about 3 hours labour . I also had a valve set done at the same time. After this was all done my engine ran ALOT smoother and i picked up 4/10's mpg. I honestly couldnt say if it was the vva or top set that made the difference but if you are getting a top set done then have them check the voltage to the solenoids on the vva's. And if your getting just vva work done them go ahead and have the top set done at the same time. My engine is idling very smooth and is running overall a whole lot nicer than it was before the work was done. Also i was told that clean engine oil is imperative to the vva longetivity , especially look out for high soot levels as apparently this can be very bad. This was not the issue with mine but was just advice from the mechanic who did the work. I dont know how cold weather would affect them as you asked in your original post but if its idling rough get a top set done and the vva solenoid voltage checked and go from there. I think that the vva's are very precise and you would probably get a code and possibly go into limp mode if you have a problem with them. A couple of weeks after having the work done my engine went into limp mode. I went to a local cat dealer and had it checked out, it was the electrical plug in the solenoid not connecting properly and thats all it took to go into limp mode. I would recommend going to CAT for this kind of stuff if you dont have a regular mechanic who works on you truck as its all very precise stuff and you really want it done right, also if you need parts you gotta get them from cat so if your allready at a cat dealer then more chance of them having them and you not waiting around for parts. Just speaking from my experience, good luck and hope it works out for you.

 

I would say the overhead has got really tight on a valve or two or you have a bad IVA thats letting some oil through when it shouldn't be and trying to open one of the intake valves a little bit. Its possible that a good over head will fix this because they will set the IVA s too while running the overhead its acually part of it. but if that don't fix it you either have a bad IVA assembly or a malfunctioning solonoid that bolts to one of the IVAs. You should let them do a IVA performance test aftet they run the over head to see if they all will pass like they should. good luck with everything.

 

That was the way I thought as well. Had both done and really wouldnt know if it was one or the other. I was just happy it was running good again LOL.