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Old 10-09-2010, 06:21 AM   #1
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Default Rough cold starts with a 2.4L Twin Cam

I have an Alero with a 2.4L Twin Cam engine. It'* a 2001 model that was driven hard by my sister for four years since 2006, and it now has 180K miles having started with around 120K when we bought it.

From the factory, it has a speed density tune, and there used to be two air boxes with one of them simply sitting on the throttle body. That one broke at the ring where it sat, and so I replaced it with a tube that goes to the now single air box. This may singlehandedly explain the cold starts as they're not so bad now that I suppose the engine has gotten used to the new setup under the newly cold weather.

However, I'd like to make sure. What are some decent ways to check? I'd like to do a compression test and have a tester ready to go, but first I'd like to sit back and think about it. When I started it in its first cold weather since the new air intake was installed, it started rough and idled for about 2 seconds as if it had monster cams; then I noticed a cloud of smoke that erupted out of the exhaust, but all things went back to normal after that.

So, all in all, with rough driving and poor maintenance for 60K of its latest miles, this Alero could have bad rings, valve seals, etc. First, I'm going to slap some Seafoam into it and enjoy the amazing smoke show. I'll run cans of Seafoam until there'* either minimal or no white smoke out of the back. Then I'll do a compression test. What else should I do? Any general guesses about the rough starts in cold weather?
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Old 10-09-2010, 09:08 AM   #2
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My first thought is carbon build up. So seafoam should deal with that. Clean the throttle body as well. Could be a sticking idle air control, if it has one. But the cause of the rough cold idle is going to be linked to the air intake between the filter and just past the throttle body. Check all sensors in that path, as well as and vacuum lines that may be cracked including the EGR.
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Old 10-09-2010, 12:34 PM   #3
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Thank you so much! That is very helpful advice since it helps me work out what I've been trying and what else to do. So far, I have cleaned the IAC valve. It was pretty nasty but wasn't too bad. I have no idea about where the EGR is, but it should be on the back of the engine by the firewall since that'* where the exhaust comes out. There'* just one sensor in the air intake before the TB, and that'* the IAT sensor. I cleaned it up and I have it in an tube that I've fitted with glue & RTV to hold the sensor. I'll try again with another sensor, though, just in case.

Do you think I should go to a JY and get a replacement stock intake? I'm having trouble reasoning it out since the first one was so bad. I've looked at aftermarket intakes with bent metal tubing, and they are naturally way different from stock. It wouldn't make sense to make and sell those consistently if they caused issues. One more thing I can think of is that the crankcase ventilation simply goes to the intake without a valve. I re-routed it to go to a PCV valve and a filter so that the intake simply takes in clean, non-oily air.
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Old 10-09-2010, 02:00 PM   #4
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It'* possible the PCV is the problem. I would look t how that is routed differently.
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Old 10-10-2010, 11:22 AM   #5
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I could shorten the pretty long tubes so that the filter sits sooner on the timing chain cover. Should I mess with that, or should I go ahead and route it back into the intake?
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