05 LS Rough Idle in Gear, perfrect idle in Park?

[savatreatabvr]

I just bought my daughter 2005 Cobalt 2.2l LS, it had been sitting for a while so in order to get it running I had to put a new battery in but it fired right up. The drive home was a bit disappointing though, it ran really rough/vibration, I can feel it in the steering wheel while in gear but as soon as I put it in neutral or park it smoothed out.

I stopped at Autozone and bought new spark plugs, oil, oil filter. Put all that in but it still does the same thing. Mow I'm wondering if replacing the front motor mount and rear transmission mount would help?

I also did a compression test and all four cylinders are at 160psi plus I checked for vacuum leaks and found none. Any ideas on whats causing the rough idle.vibration?

I like the car, I think it's a good first car for my daughter but is it easily fixed or should I get rid of it before it cost me big time?

 

[YelloEye]

Is the vibration speed dependent?

 

[savatreatabvr]

Is the vibration speed dependent?

The vibration smooths out when I press the accelerator. I replaced the front motor mount and the rear transmission mount yesterday and the idle smoothed out a little in gear. There is still a noticeable vibration on the steering wheel but it idles smooth in park so I think I can rule out vacuum leaks. I also sprayed throttle body cleaner in the throttle body but not much change. It has 160psi compression on all 4 cylinders but it also has around 170k miles so I'm wondering if I should rebuilt head or something?

 

[YelloEye]

Ah, so RPM dependent. There's 2 more mounts on that powertrain and from what I recall there's a certain order to getting everything torqued down so that you aren't preloading any of them.

What RPM is the engine idling at when in gear and you feel the vibration? I assume you replaced the mounts with OEM rubber mounts?

 

[savatreatabvr]

Ah, so RPM dependent. There's 2 more mounts on that powertrain and from what I recall there's a certain order to getting everything torqued down so that you aren't preloading any of them.

What RPM is the engine idling at when in gear and you feel the vibration? I assume you replaced the mounts with OEM rubber mounts?

Rpms seem low at about 800 and I replaced the mounts with the low priced ones since I'm not sure if I', keeping the car yet. I did see one mount by the passenger fender (front of engine) but haven't located the other one yet.

---------- Post added at 02:17 AM ---------- Previous post was at 02:03 AM ----------

I was told that bad oil rings on the fuel injectors can cause vacuum leaks but the engine idles smooth when in park or neutral. I'm used to older chevy 454 and 350 v8s where a vacuum leak has tell tale signs. These little 4 bangers are a whole different ball of wax!

 

[YelloEye]

If you turn on the defroster does it get worse?

In all honesty, without a video or seeing it in person, that 800RPM vibration sounds normal.

All 4 mounts are shown in this picture: 1, 6, 11, 17

 

[savatreatabvr]

If you turn on the defroster does it get worse?

In all honesty, without a video or seeing it in person, that 800RPM vibration sounds normal.

All 4 mounts are shown in this picture: 1, 6, 11, 17

Excellent diagram, thank you! Yes the idle lowers and gets rougher when the rear window defroster is switched on.

 

[YelloEye]

If you need part numbers for those mounts try checking wholesalegmpartsonline.com

They might not have the best prices but at least you'll know the part numbers you need.