car: 2009 Cobalt SS
mods: GMS1, catted DP, intake and catback

it's not that noticeable in the video but the exhaust flutters at idle. it's very noticeable in person and it's more noticeable at the end of the video but you probably need headphones or good speakers lol. no drivability issues.. the car runs fine. no CEL, codes or loss of power (that I can tell at least). ltft is 3.9% so it's not that bad. rpm and boost don't fluctuate. basically, it's just the volume of the exhaust that fluctuates. it only happens after the car is warmed up and used to happen before I got the DP but can't remember if it was before the intake and exhaust or not. is this normal?

update: rpm flutter while cruising in neutral at highway speeds (80 kph/50 mph or higher). jumps up and down between idle rpm (~750) and 1100 rpm

 

Sounds like something is vibrating

 

couldn't hear a thing. maybe ill hear it in person soon? haha

 

yea, possibly

haha you probably will

 

I can hear it ...... it has a rhythm to it almost like cams. Does the vacuum gauge move around much at idle? How many miles are on it ?

These cars can gum up the intake valves pretty bad .... I would seafoam it and see if it helps .

 

Do not seafoam ur Di engine. Boost the **** out of it and get it nice and hot and go for a highway cruise

 

yes, it does have a rhythm and it's always the same rhythm when that happens.. very consistent. I forgot to mention that I have the rough start up issue that same people have had, which is supposed to be related to the cam phasers. there was a PI for it. I took it to the dealership twice with the PI but they couldn't duplicate the noise and said I have to wait until it gets worse and they can duplicate it.
it never throws a CEL or a code tho and never bogs or loses power.

no, the vacuum gauge is pretty still at idle. it has almost 60k km/37k miles. don't know about sea foaming.. I know about the gumming up issue


I heard about the intake valves gumming up because of DI but I often read comments warning against seafoming like above ^ so not sure what to do..

 

Any reason why you say that? I've seafoamed mine at every oil change for the last 40K miles without any problems. Car traps 111 mph so it hasn't hurt it any ... plus it really seems to help smooth out idle.

 

Never heard about not seafoaming a direct injection engine but if you were worried about it, just don't put any in the gas. Find a good vacuum source and let it run through there so it will clean the valves up good

 

Yep.... thats how i use it. I havent put any in the fuel or oil .

 

Yea, I wouldn't mix it with gas since it wouldnt really run by the intake valves anyway. I'm just concerned cause I've read a few times that you shouldn't but never really read why. I actually did go for a highway cruise and maxed boost a few times and it seems to have gone away for now but I still want to seafoam cause I'm sure there's some carbon buildup. Anyone who thinks you shouldn't seafoam a DI engine, please chime in as to why

 

my car seemed to run a lot better after i seafoamed it.. i couldn't tell anything from your video, but from your description, my car's havin the same thing goin on.. I'm at ~39k miles an while rollin in neutral, or sittin at a light, Rpms'll move like you described, an my my boost gauge would jump up about 8-5hg, then go back down in sync with the RPMs..

no reeeaaall problem jus yet, powerwise, but i dont wanna be ridin round thinkin everythings ll kosher, an pop somethin ya dig?

 

yea, that's exactly what I'm worried about.. besides rolling in neutral and idling, the car seems to run fine but if whatever is causing this could eventually break something, I want to get it fixed before it breaks

the idling problem is actually back after being gone for a day so I might take it to the dealership and see what they say. I'll post the updates

 

I'm not entirely sure when it started, but I started noticin on my car maybe a couple months back when I replaced my stock intercooler.. I'm thinkin I got a boost leak somewhere an its causin the fluctuations.. Praly my intercooler.. But I've had my car at the dealership, described the problem(among a mess of others at the time...) and they couldn't replicate it enough, an said it's probably not a big problem. "Doesn't sound like one", Is what they said..

 

this idle flutter... I think I notice it in my car too. Car runs strong so I dont worry about it but it does have a rythum. I seafoamed my car at 60,000 miles. Im at 63k now and the rythum has always been there so I just ignore it. I WILL say.... Its wayyyy more noticeable (actually entirely noticeable) with the tune on then with the factory tune.

 

I hate when they say they can't duplicate the problem..

yea, I've been ignoring it for a while too because there are no issues that I noticed but I wanted to see what others thought. plus, I want to hit a strip this summer so I want the car to be running right do you have flutter while rolling on the hwy in neutral or just while idling?