Rough Idle Diagnosis

[Trav]

Originally Posted By: Merkava_4
It could be a partially clogged fuel injector. I used to have that problem when I was buying Arco gas. Switched to Costco Top Tier gas and after about 5 tank fulls, the idle returned to smooth.


The 2007 Ecotec seem to have dirty injector issues, nothing severe the flow and pattern seem to get screwed up easily with these units for some reason. I have seen them with low miles on them and had issues, one would vibrate when you let the clutch out, not smooth at all but idled fine.

OP. Try a full tank with a can of Berrymans Chemtool in it (put the Chemtool in first so it mixes) run it low without running out of fuel and then a bottle of Redline SI-1 (O’Reilly has it in stock) in a full tank. As long as no CEL is one I have a feeling you problem will help.
These are different chemicals for different issues no single product does it all well. The PEA takes care of carbon and hard deposits at the nozzle better than anything but varnish and other non hard deposits on the back side of the disc or pintel are better addressed by the Chemtool. A double prong approach that cost less then $20 is well worth a try IMO.

 

[WobblyElvis]

Perhaps you should consider a professional diagnosis from a skilled tech with the right diagnostic tools. If you plan on keeping this car for long this is probably the best option. Many faults, even minor, can cause damage to an engine if left unattended for a long period of time.

 

[Trav]

Originally Posted By: RoGuE
Can anyone give me an opinion on if these spark plugs look bad?

http://imgur.com/a/6IjQs


It looks like you may have lost the ground electrode puck on the one you say look at the hole. Hard to tell from the picture but it happens. I would just replace them.

 

[mk378]

Have you looked at all 4 plugs yet, or just one?

If it's running real rough, the test where you kill one cylinder at a time (best done by unplugging the fuel injector) can help to tell if its something related to one particular cylinder or a general malaise.

You don't drive a lot of miles, is it possible that the gas in the tank is stale?

 

[RoGuE]

Originally Posted By: Trav
Originally Posted By: Merkava_4
It could be a partially clogged fuel injector. I used to have that problem when I was buying Arco gas. Switched to Costco Top Tier gas and after about 5 tank fulls, the idle returned to smooth.


The 2007 Ecotec seem to have dirty injector issues, nothing severe the flow and pattern seem to get screwed up easily with these units for some reason. I have seen them with low miles on them and had issues, one would vibrate when you let the clutch out, not smooth at all but idled fine


Funny story, I looked up the Carfax on this a couple years back and at only 324 miles all the fuel injectors were replaced (I purchased the car with 7500 miles on it already in 07)

Originally Posted By: Trav
Originally Posted By: RoGuE
Can anyone give me an opinion on if these spark plugs look bad?

http://imgur.com/a/6IjQs


It looks like you may have lost the ground electrode puck on the one you say look at the hole. Hard to tell from the picture but it happens. I would just replace them.


I might just do that, they're only about $6 each and there is a rebate from ACDelco that makes them only $3 each.

Originally Posted By: mk378
Have you looked at all 4 plugs yet, or just one?

If it's running real rough, the test where you kill one cylinder at a time (best done by unplugging the fuel injector) can help to tell if its something related to one particular cylinder or a general malaise.

You don't drive a lot of miles, is it possible that the gas in the tank is stale?


It shouldn't be stale, I fill it up about every three weeks. I only drive about 22 miles a day to work and back (and for several years less than half that at another job)

 

[gregoron]

Have you checked all vacuum hoses? With EFI engines with no PCV valve, crankcase ventilation is through the crankcase by vacuum pulled by the intake manifold when the throttle plate is closed off during idle. Any vacuum leak downstream of the throttle plate will cause rough idle. Check for obvious vacuum leaks through the oil cap, oil dipstick O-ring, vacuum lines & connectors. Check your Purge Valve or Gas Vapor Regen Solenoid if it's stuck open.

Good luck.

 

[Piston_slap]

I think I could fly my Bell 421 through that gap!

 

[RoGuE]

Originally Posted By: gregoron
Have you checked all vacuum hoses? With EFI engines with no PCV valve, crankcase ventilation is through the crankcase by vacuum pulled by the intake manifold when the throttle plate is closed off during idle. Any vacuum leak downstream of the throttle plate will cause rough idle. Check for obvious vacuum leaks through the oil cap, oil dipstick O-ring, vacuum lines & connectors. Check your Purge Valve or Gas Vapor Regen Solenoid if it's stuck open.

Good luck.


What is the procedure for checking the purge valve?