Vacuum leak???

[jan_mast]

So I have an 08 Cobalt with the 2.2 L engine. I had misfires in #1 cylinder and loss of compression. Pulled the head off and replaced the following components: head gasket, head bolts, intake manifold, valves (#1 cylinder) and valve springs.

The valve job corrected the loss of compression in the number 1 cylinder. I still have misfired, but they are random cylinders. At stop or at idle, the car idles really rough and lurches when I accelerate again. Also been getting bad gas mileage. I already replaced the air filter and cleaned the inside of the throttle body? Any suggestions!? Thanks is advance.

 

[Mike571]

So I have an 08 Cobalt with the 2.2 L engine. I had misfires in #1 cylinder and loss of compression. Pulled the head off and replaced the following components: head gasket, head bolts, intake manifold, valves (#1 cylinder) and valve springs.

The valve job corrected the loss of compression in the number 1 cylinder. I still have misfired, but they are random cylinders. At stop or at idle, the car idles really rough and lurches when I accelerate again. Also been getting bad gas mileage. I already replaced the air filter and cleaned the inside of the throttle body? Any suggestions!? Thanks is advance.

Just glancing at what you said real quick if say check your timing. I used to have an eclipse that was acting a lot like that and it turned out my timing belt jumped a few teeth but didn't throw a code. going off what your saying I'd bet that's probably not it but it's worth checking the timing marks on your cam gears

 

[jan_mast]

I do appreciate the suggestion but with these cars it won't line up.

When we retimed it we took the crankshaft cover off and made sure that all the timing marks were right on. The first time I tried to do the timing without looking at the mark on the crankshaft and I got mad codes like position sensors don't agree and what not.

Then we turned the crankshaft a couple of revolutions with a wrench and almost crapped my pants because the timing marks didn't line up again. Lol

 

[YelloEye]

Once you have lined the marks up it takes a lot of revolutions for them to match up again.

 

[jan_mast]

Yup! After changing my shorts I found a forum post that explained. Then I buttoned her back up and she started with no codes. Later I started getting the multiple misfires code.

I still have what seems like a damn vacuum leak though. I sprayed carb cleaner around the intake manifold and throttle body, but that didn't change the RPMs at all. I noticed when I sprayed around the #1 injector I would get a hissing noise, but no additional RPMs. I'm lost.

 

[jan_mast]

So I took it to a mechanic and he confirmed that it is a vacuum leak. He says it's leaking at the air intake manifold towards the #1 cylinder.

WTH!? I just replaced that intake manifold and it came with all new gaskets. Is there a set of aftermarket gaskets I could use? Or some type of sealant? I don't recall the factory service manual calling for ATV or anything like that.

Not sure if I should take the manifold off and inspect the gasket again or buy a new gasket set....

 

[YelloEye]

OEM gaskets should seal fine on a clean surface. Have a look at the space I suppose, might be something stuck in there or the intake manifold might have an imperfection that's not letting the seals do their job.