Rough idle, and brief drop in RPM - Chevy Colorado & GMC Canyon

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Old 12-03-2011, 01:54 AM   #1 (permalink)
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Default Rough idle, and brief drop in RPM

When I first joined up on this site I had a rough idol and drop in rpm problem and it was suggested that I clean my throttle body and my MAF sensor, it took awhile for me to get around to it but I cleaned the throttle body and the MAF sensor, I also changed my plugs to Bosch Platinum+4's. It is odd but sometimes it will idle rough then other times it wont and run smooth, as for the dip in the RPM's I originally reported that it would do it about every 40 seconds, after the cleaning it will drop in RPM and shudder but not as often as before. Any other suggestions?

06 Colorado 3.5, with recently replaced head for valve issue.
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Old 12-05-2011, 10:05 PM   #2 (permalink)
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replace your map sensor back top right of the motor just did mine no probs at all
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Old 12-09-2011, 10:43 AM   #3 (permalink)
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I changed my map sensor, there was some improvement, although there is still a drop in the RPM's but not as often as previous. The vibration is still there, although I have noticed that the vibration is more noticeable when it is drive. I haven't had any check engine lights, so I am wondering if a sensor could be malfunctioning but not to the point that it is setting off the check light. Also what is normal idle speed for the 5cyl, mine sits at about 600 when warm. Also when I replaced my plugs it seemed that it was running rich. also one more item that is odd even though it is winter, my mileage is really bad, last fill up I had 13 mpg with city and highway.
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Old 12-10-2011, 12:47 PM   #4 (permalink)
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i was having the same problem except mine wasnt rough idle it just dropped rpms. I poured some injector cleaner in the tank and seemed to help it quite a bit.
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Old 12-10-2011, 05:24 PM   #5 (permalink)
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i had my idle rpm raised when i got my tune, helped out, but it does dip sometimes when i am driving and i stop at a light or somethin but does it a couple of times and then its good...so idk... i have cleaned my tb, and just got my fuel injectors cleaned
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Old 12-13-2011, 06:59 AM   #6 (permalink)
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I have run Chevron's Fuel cleaner through the engine about 2 times since the head was replaced, and I run Chevron only if I can. I also run 90 in it. would it be running rich because of the octane that I am running? vibration still unsolved as of yet, one website says that it may be a misfiring cylinder, but you would think that they would have caught that, or fixed it when the head was off, plus no codes.
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Old 12-13-2011, 11:27 AM   #7 (permalink)
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Octane will not make a vehicle rich or lean, and you don't need to run 90 unless you are experiencing issues with lower octanes. Stock, lower octane is fine.

Mine idles at 650.

You might be rich if you make short drives. Now that it's colder outside, it runs in cold loop for longer, therefore making it rich for start up and warmup periods. If you don't drive longer distances or long enough time for the engine to reach and maintain normal operating temperature you will not be burning as clean as you could be. Also, is your temp gauge running at normal range or is it cooler?
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Old 01-08-2012, 09:16 PM   #8 (permalink)
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More details would be helpful. Keep track of when it happens. I have the same problem on my 07 5cyl w/73,000 miles. The rough idle only happens after a 1 1/2 to 2 hour shut off. It makes me think its a leaky injector dribbling fuel into a cylinder and then misfiring while it burns off. On a short time span the fuel leak wouldn't affect it as much and a longer time would allow it to dissipate. I'm putting some injector cleaner through this week to see if it helps. If no change, I'm going to have the fuel system cleaned.
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Old 01-31-2012, 06:04 PM   #9 (permalink)
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I have run objectors cleaner through mine, I was using the cheveron stuff, then I ran a bottle of Lucas cleaner through it, I just can't ever get it to vibrate consistantly, sometimes it will he so bad that the dreading wheel is going up and down and I have to press the gas to idle it up to **** 8-9 hundred rpm other times it will run as smooth as can be. As for my temp gauge it is within normal temps after about 3-7 minutes of driving. Some suggestions that I have found are a short on one of the coils, but every time I think it is something it couldn't be because I'm no throwing any codes so there isn't anything to off of, would a short throw a code?
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Old 01-31-2012, 11:38 PM   #10 (permalink)
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How about the ignition wires? are they old, worn or maybe only one is faulty?? If the engine was taken apart maybe you have a vacuum leak somewhere? My old Dodge had a vacuum leak, ran rough as **** in wet weather (why it ran better in dry I never figured out), but fixing the leak solved the rough engine.
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