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Trying to accelerate at idle cruise with rattle noise when accelerating...

2K views 4 replies 1 participant last post by  Wolf_22 
#1 ·
I have a 2006 Chevy Colorado 2.8L w/ about 145k miles on it. This morning on my way to work, I was on a street going about 30-40 mph with my foot OFF the gas pedal and the RPMs were pulsing with the truck trying to accelerate with each pulse. It did this for about 50 yards. I noticed it after about 20 yards and when I noticed all this happening, I could also hear a sound outside my passenger-side window that sounded a little like a rattle. My brakes are perfectly fine, but I noticed that when I slowed down, the truck was still trying to do this "pulse thing" and since I was a ways from my turn, I decided to press down on the gas pedal. Once I did that for about 10 or 15 yards, it all stopped and the sound disappeared. Everything back to normal.

I'm not sure what's going on with this but this is the first time this has happened. It scared me a bit.

The last issue I had with this truck was last winter when it had a problem starting. The truck would try to turn over but end in a low screech. It did that for about 10 minutes (I tried to start her about 3-5 times with the final time ending in success.) It was the only time that had happened but I brought her into my local Chevy dealership a couple days after that and the mechanic made it sound like the engine's oil rings might be worn down because they said they couldn't see any oil on the dipstick when they checked it (which is crazy because I'm 100% on top of my oil changes--every 3k miles, always a new filter, no leaks anywhere; I go over the entire engine every time I do my changes and always use 5 quarts like I'm supposed to with SAE 5W-30.) Anyway, the mechanic suggested adding maybe about 1/2 to 1 more quart more when I do my changes, which I've started doing to be 100% safe with oil amount, but he also made it sound like the timing chain could be on the way out and that if I'm not wanting to swap the entire engine, that I should get the chain swapped, which will run me about $2k at a mom-and-pop shop who also quoted me around $7,800 for a new block (minus other componants, but if I go that route, I'm going to save up to about $10k to hopefully get a new starter, a new power-steering pump, and a few other things if possible). I was hoping to hold off until about August to take the truck in to have it looked at a little closer because that would be the time I'd decide on something, but with this morning's issue, I'm worried that I need to take her in as soon as possible now.

Back to this weird revving / noise issue, does that sound like a chain skipped a tooth and that my pressing on the gas got it back in timing or does this sound like a transmission issue? The transmission is getting some age on it (I had it swapped by that mom-and-pop place back at like 90k-something miles or sometime around 2013) but I've not had any issues with it that I can tell. It goes from from park to drive, etc. without any issues. I can't imagine a transmission would make the noise I heard this morning, too, but considering it was acting almost like it was having problems coming out of a gear or something when my foot was off the pedal, well, I can't tell.
 
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#2 ·
Point of clarification: no codes appear to be getting tripped. I don't see any check engine lights and one of the people I just got off the phone with at the mom-and-pop shop suggested cleaning the throttle body to see if it helps as I won't be able to get the truck in to see them until the 17th. I said I'd give that a try and see if it helps--I've cleaned it before, it's pretty easy to do. I asked him if he thought this would be a timing chain / tranny issue and he said he doubted it. If the timing chain was having problems, I'd more than likely see a DTC being tripped and since the transmission appears to be working without any issues, he just didn't think it was either of those things. Of course, it's impossible to know for certain without bringing her in.

So I guess I'm going to try and clean the throttle body out as long as I get home tonight without any issues and see if that helps. If it doesn't, then I'll take her in and get her checked out.
 
#4 ·
(I've posted about this over on the 355Nation site, too, but since I posted here, I thought I'd continue to update this until I get this thing fixed.)

Update: Went out to my car after work, started her up and drove to a local gas station. Everything was fine. After that, I drove to a grocery store, plugged in my ODBII reader, and the "pending" p0017 code was magically gone. Great! Then I drove it home from there and it made the rattle noise when I came to a stop sign about 1 mile from my house (but this time, I couldn't feel it trying to accelerate). It seemed like acceleration was a little off, but as soon as I gave it gas to get the RPMs above, say, 1500, the noise went away. As soon as I got her into my garage, I plugged the reader back in and not only was I seeing the P0017 code, but this time I also saw a P0106 (which read as "Manifold Absolute Pressure / Barometric Pressure Circuit Range / Performance").

The mom-and-pop place quoted me for about $2,800 for a timing chain replacement and I think I'm going to just bite the damn bullet to get it done. I have the money to do it (thankfully) but man, this sucks. I'm going to see if I can get her in there tomorrow first thing and just let them have at it. They'll do a diagnostic but if it turns out to be the timing chain change, the guy said they'd waive that.

This is so depressing, but if it's gotta be fixed, it's going to be fixed.
 
#5 ·
Update: It's in the mom-and-pop shop's hands now. The long and short is that they'll open her up to see what's going on. If the entire thing is blown, I'll be forced to plop a new engine in. Otherwise, if everything else besides the timing chain assembly looks good, I'll just replace that for now. Not sure when they'll get to it but as soon as I know more, I'll provide another update.
 
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