I have an '09 LNF with just over 100k on her. When the engine is cold, at idle it's fine, but when in gear and driving the engine is rough and stumbles as well as hesitation in power. If I give it more gas I get nothing back and boost remains low (~<2lbs) even at half throttle. The whole car feels like it's going to stall.

This would originally only happen on really cold days (<15F), but started happening on warmer days and now happens all the time, even if it's 80F outside when I start the car. I generally have to completely baby the throttle until the engine full warms up and then it's fine. I have basic boltons, a trifecta tune (@41k miles in 2012 for 93 octane) and I always run 93 octane. I haven't done any real engine maintenance as of yet, so everything is still OEM. Once the car warms up it's absolutely fine, I can mash the throttle and it will hit 20+psi and rev beautifully all the way to redline.

I was soon planning on removing the intake manifold to clean it, the throttle body and intake valves as I am sure they are very gunked up from time and I was going to hit up some other maintenance items (timing chain tensioner, serpentine belt, fuel filter, etc.). But before I do that I was wondering if anyone had any other things I could possibly look at that could be causing this?

 

First of all take trifecta off before you do more damage, lol.

And likely just very coked up valves. There is a cool walk through on here of cleaning them With walnut blasting

 

Sounds like a tune problem. Your spark is probably all over the place when the VVT is using the cold cam tables. Pretty common issue for cars with aftermarket intakes, charge pipes, and/or downpipe that haven't been tuned properly for cold/startup idle.

 

Thanks guys. I'm definitely going to be doing the walnut blast shortly. I've started researching that and hoping to do it in July. I'd agree with the tune being an issue, I did have it "tuned" for the parts I have on it. As I did the boltons first, then got the tune. If this was the tune though, shouldn't I have seen in 5 years ago when I got the tune? This started becoming an issue sometime about 3 years ago but not enough to even warrant a question on here. What I'll do is next time I drive the car I'll flip the tune off and see what happens.

Thanks for the advice guys!

 

It is probably a combination of the valves being coked up along with the tune. Cleaning the valves will probably help a lot but eventually it will start doing it again.

 

I'll be cleaning the valves in the next month or so. In the meantime, I have tried a handful of times to disable the tune when cold and indeed, the problem is gone. So my solution for now is to just leave the tune off until the engine is warmed up. I'll try and remember to update this thread with my results after cleaning the valves.

 

Personally my car ran so much better with a hp tune verses the trifecta I ran for 1 yr because it was never dialed in for the car. I sent logs back and they said it needed no tweaks. Which was not correct. If you think it runs decent on trifecta you would really be happy with a good tuner and hpt.

 

This weekend I did the walnut blast and the hesitation and stumbling is completely gone. Thanks for the advice guys! This worked beautifully! Now it's time to do my timing chain.

 

Good to hear!