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Old July 28th, 2015, 3:00 PM
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2001 Silverado 5.3, Only rough when Cold.

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Old January 4th, 2012, 10:22 PM
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IAC only controls idle speed and nothing else. You should not listen to anyone that suggested that at all. Keyword in in Idle Air Control is Idle.
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Old January 5th, 2012, 10:28 AM
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Same EXACT thing happened on my 03 Silverado with the 5.3. Intake manifold gasket was bad. While you're intake is off, I would clean that up nice and good. Mine was plenty dirty from the gasket being bad for so long.

To test, start it cold and when it's acting up, spray carb cleaner around the intake manifold. My bet is that the rough idle clears up. That's your huckleberry.

Turns out the Silverados were known for their bad intake gaskets, much like the Blazers were. Why GM didn't use a quality gasket is beyond me. Felpro makes a better gasket that will likely not need replacement. Worth the money.
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Old January 6th, 2012, 12:33 PM
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I replaced the intake gaskets with the Felpro. Old ones were shot, and the head was gunky and dirty. Also cleaned a bunch of crud off the injectors and intake manifold. Seems to have fixed the problem. Started cold this morning and ran fine. Supposed to be back in the 20's next week; that will be the real test.
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Old January 6th, 2012, 9:30 PM
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It is most likely fixed. Please post back next week and let us know.
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Old January 5th, 2015, 2:29 AM
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Originally Posted by Jared Phillips View Post
Truck has around 150K miles and runs like new!...after it's warmed up.
After it sits all night, it will still fire right up, but shakes and shudders and won't hardly idle as long as it's cold. Throws code P0171 and P0174 - running lean.
I'm doing all the work myself, and just replacing parts as I can afford them. I've done search after search and get a variety of suggestions.

First I cleaned out the MAF, TPS, and intake. Got some gunk out of the intake but that didn't fix the problem. Still won't idle cold.

Next, I replaced the thermostat. Couple people suggested that. Made sense... Won't run until at a certain temperature, ok. Replaced that, no help.

Next, at the suggestion of a very knowledgeable mechanic friend, I cleaned out all the electrical connections with electrical cleaner, and replaced the Fuel Pressure Regulator and PCV valve. I just finished doing this, and it seems to idle better, but it is also around 50 degrees outside. I just know that tomorrow morning when it's 25 degrees, it's going to stumble and fall on it's face again.

I bought all new plugs too, but I haven't installed them yet. I can still take them back if I don't need them.

This seems to be a very common issue, and everyone has different variations of the problem and different solutions.

If anyone has this exact issue - rough only when COLD, but does start every time - and runs perfect when warmed up after a few miles... I would appreciate any advice from your experience correcting the issue. Thanks in advance!
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I have exact same issue. I even replaced all 4 o2 sensors and still sputters and misses in colder temps.
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Old January 8th, 2015, 10:22 PM
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Similar issue on my 00' Silverado Ext Cab. My case was I did new sparks, cleaned TB and new valve cover gaskets and new fuel filter. Still dying when I tried running it, turned out to be a bad battery.

Changed it and starts right up after second start. First start, it sputters and revs trying to stay on, just shut it off and crank it again. Will rev a bit but quickly stop. Let it run itself dont throttle it or you might kill it. Happened to me. Bring your phone for ( incase call for jump) and take it for a spin. Turn off and turn on again to see if problem persists. Also get alternator checked. Cold weather screws up these two systems from my experience.
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Old April 12th, 2015, 9:07 AM
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the new intake gaskets fixed that problem. Now a few years later, I'm at 212K miles and I have another issue.

I'll post it here and also in a new thread.

Randomly will not start. It cranks fine but will not fire. One day its fine, the next day, nothing. Thought it was the fuel pump; replaced it twice. Replaced all the pigtails and connectors at the tank, too.
When this happens, the fuel gauge reads empty and the message center says "Low Fuel". The Fuel Pump is simply not getting a signal.

Yesterday, I accidentally made it start. I was messing with the relays, swapping out the fuel relay with others. I used a test light and verified I had voltage at the relay when the key was on. However, I only had it at one of the four legs. If I used a wire and jumped the terminals, I could get it to click and I heard fuel pressure in the rail. Yesterday, this made it start and it ran and started fine all day. Today, it won't start again. I tried to duplicate my "repair" with the relay. I jumped the terminals, and hear the fuel pump kick-on and heard fuel come in the fuel rails on the motor. Cranked but nothing. Then it sounded different when cranking. I'm afraid I may have flooded it, due to fuel being pumped-in and it not starting.
I think my PCM might be bad? That would explain why the fuel pump and other components aren't getting a signal to start. Again, it cranks fine, just won't start at random times.
On one occasion, I had a rollback haul it to a shop. It would not start to drive on the rollback. 9 miles later when he arrived to the shop, it started and drove off the truck and of course they could not duplicate the problem.

I am at my wits end with this gremlin. This has been the best truck Ive ever owned, 212K miles and runs strong. Just bought a 2002 Suburban with the same drivetrain. Now I'm regretting that, if I'm going to be chasing gremlins in it in a few years.

Any thoughts?
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Old April 12th, 2015, 12:24 PM
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Since posting the last reply, I found a few threads online where the 20AMP fuse for the ECM was bad. Once I got home, I checked it and sure enough it was blown. Replaced the fuse, and after cranking a bit to cycle through the fuel that was flooding it, it started easily.

So, now it makes sense, the ECM wasn't getting voltage which means it wasn't sending signal to the fuel pump relay. So now I'm wondering what caused the fuse to blow? And why was the problem intermittent? One day fine, the next day won't start? And then a few hours later, it starts again? The 20amp fuse was labeled "ECM B". I'm curious to how this wiring works. How would a blown fuse be intermittent? If its blown its blown. Still doesn't add up, but at least it started. Guess I'll get a pack of 20amp mini fuses to keep on-hand should it decide to blow again.
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Old November 13th, 2016, 10:47 PM
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I have the EXACT same problem. As the mornings got colder the trouble got worse. Today I found a missing fuse for one of the O2 heaters. That didnt' fix the issue. What fixed it was unplugging the Mass Airflow Sensor. It's about 32 degrees this morning and even after the new fuse it was fine for 30 seconds and then started getting lower and lower rpm and rougher until it finally died. I unplugged the MAF and restarted the engine. No lag, no rough idle. It was smoothly running at 800-900 rpm (or thereabouts.)

I know I still need to change the O2 sensors, catalytic and knock sensors because of the codes I'm getting but this is one hurdle I was really worried about crossing. Now I just need the $200 for a new MAF.

Hope this helps y'all.
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Old December 16th, 2016, 11:28 PM
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Thanks Erik. Truck almost didn't make it home in the first snow storm of the year. After running through all of the common problems including cleaning the MAF, simply unplugging it fixed the issue.
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