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Discussion Starter #1
I've been experiencing this problem for quite a while now. My 07 Chevy Colorado Z71 2wd surges rpms between 1000 and 400 when coming to a stop. While stopping it also dims headlights. I've tried cleaning the TB and the MAF but still no luck. So today I went to AutoZone and got my battery and alternator tested. The battery that was in my truck was a piece of crap so I got a brand new battery. Went back and had it tested again and the test showed the battery was good(obviously) but my voltage regulator had failed. Would replacing my alternator be the fix? The truck also has 110,000 miles, new plugs, new air filter, new battery, cleaned TB, and a cleaned MAF. MY PCM was checked and it had quite a few updates also needed for the computer. I have been looking into this on 355nation and C'Fans and still haven't had anything match my problem. No CEL's.
 

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Tranny not downshifting,torque converter not unlocking----assuming you have an automatic--just guessing!! Your head.lights should dim when the rpms get that low.
 

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When my truck had this problem it was the TB ..very dirty also the vent valve for the gas tank went bad. but mine was throwing codes..
 

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The headlights dim how much?
Barely noticeable, or very noticeable?
 

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I had the same issue on my 05 - I5, so much so that I'd get a "Low Idle" code but it gave no indication of the reason. Turned out it was LOW VOLTAGE when I had a friend hook it to a Snap On stationary unit. I replaced the stock battery terminal ends on the cables, checked my ground wire connections at the body and cleaned them, and did a tune up. This kept idle above 600 rpm but it was still rough. Finally cured at 130k when I again cleaned TB & air filter. did plugs then bought supersparks from super modulation on this site. The supersparks brought idle up from 500ish to 700 or so and completely smoothed it out. I'm not marketing the product even though it seems like it; they just worked for me.

Oh, I also flushed my cooling system, did thermostat, and began using Peak Global coolant at the same 130k mark but don't think that helped idle. About the same time I did a trans service with fluid and filter and replaced the exhaust camshaft timing actuator. These service items didn't affect the idle but helped with high rpm performance for sure. You might want to put them on your to do list:)
Good Luck.
 

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I'm pretty sure in Post #1 he indicated that he cleaned the throttle body. There was no description of how it was cleaned.....but he has cleaned it. The symptoms direct us to a dirty throttle body, however in this case it seems to be a deeper problem.
 

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Discussion Starter #13
The headlights dimming are very noticeable. I'll clean up the TB again, throw a new alternator in it and see what happens. I also put in a new thermostat a couple months ago. Brand new rotors and drums with new brake pads. I also put in a new air filter a couple months ago.
 

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Discussion Starter #14
Today a cylinder #2 misfire code popped up. The code only occurs when letting off the gas. Tried to replace the coil for cylinder #2 and that didn't work. So my mechanic guy things that the cylinder is running lean and the computer needs to be reprogrammed. I may be possibly getting it reprogrammed sometime tomorrow or here in the next week.
 

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I've had the same problem with my truck since at least 40 000kms (Now at 170k kms). It feels exactly like the torgue converter isn't releasing as you come to a stop. I had to replace my transmission a while ago, but it didn't change anything. I find it's worse with the AC compressor on (AC or defrost) and worse with winter gas. I'm looking forward to seeing if someone finds the solution!
 

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mine does the same thing, as does my fathers 4wd...it does it worse when it gets colder or closer to an oil change/transmission filter change
 

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Clean ur maf sensor too when it's dirty it won't read right. And causes idle problems too.
 

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That and a bad MAP sensor
True. But map sensors rarely go bad. I have a couple laying around from core engines I've parted out.
 
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