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Old 02-28-2005, 06:20 PM   #1
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Default semi-rough idle?

Today I just noticed for some reason the car seems a little shakier then normal at idle. I just cleaned the IAC 2 days ago and the idle went from bouncing from 600-1200 to completely steady at 600. I also noticed that this morning when listening to the exhaust it would be normal, but with a small pop sound at random intervals. Like....wub wub wub wub pop wub wub wub. It does that after a cold start and after being warm. There are no problems at WOT.

Other then shakiness and that occaisional popping it'* never been better. Steady idle, no SES light, no hard starts, fresh oil, and everything mentioned in my sig. Is this just an old car thing or what?
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Old 02-28-2005, 07:46 PM   #2
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Vacuum Leak. It'* like a big grind cam idle, right? That'* a vacuum leak. Could be anything.. but usually if the line is questionable, just replace it. Grab like 20' of vacuum line from Autozne, I paid like $7 for their leftovers. Replace everything you see [that is rubber of course].

The popping noise.. honestly I don't know. How loud is it? Like you have to have your ear up to the tail pipe to hear it? That'* usually the only time I hear the "wub wub wub."


-justin
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Old 02-28-2005, 08:29 PM   #3
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Vacuum line eh? This term is rather new to me. Where are they generally located and what do they do? I will inspect them soon when I know what to look for . The idle is like...I can see the steering wheel shaking and I can feel it vibrating in my hand. If the lines are generally ok, could it be a gasket or something?

I was also going to ask...could a clogged catalyctic convertor cause a rough idle? Because if I rev the engine to say 2000rpm'* it will drop down to about 1500 and slowly make it'* way back down to regular idle. I beleive that is a tel tale sign of a clogged cat?

The popping is just loud enough to be noticeable, although I just started it a couple minutes ago and it wouldn't make the sound...go figure.

But about those lines...are there any you can easily point out from a picture like this?

Thanks
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Old 02-28-2005, 09:23 PM   #4
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Okay, the vacuum lines are all distributed through the Vacuum Distribution Block. On the picture of your engine, you see the EGR Valve? Well, about one inch below that, you see a black thing with four lines coming out of it? That'* the Vacuum Distribution Block. The two on the front go to the Vacuum Modulator and Charcoal Canister. These are mostly metal, however there are some rubber connectors for a few spots. Check those carefully. The largest one goes nowhere [would have been for the power brake booster, but we have electronic brakes, so that is just closed off]. The other one I am not 100% sure where it goes, but I believe it goes to this box just to the left of the Master Cylinder. My vacuum leak was from that connection, and everytime that popped off, BAM rough ***AWESOME*** idle. If the idle was the only side effect to that, I would have kept it like that, but only having Floor Vents, slipping tranny [more so than usual], and mis-calculated fuel pressure are all things I don't want.

Now, that brings me to my now figured out what is wrong with the pop. Duh, Fuel Pressure. Okay, fix the vacuum leak, and you'll be set. The Vacuum Leak makes the Fuel Pressure [vacuum controlled] off calibration, which is why you have that pop, either from too rich a fuel mixture [because it doesn't calibrate properly upon deceleration of the engine], or it'* just too rich period. Go out there and Fix that Vacuum Leak!


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Old 02-28-2005, 10:02 PM   #5
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Quote:
Originally Posted by captainmiller
I was also going to ask...could a clogged catalyctic convertor cause a rough idle? Because if I rev the engine to say 2000rpm'* it will drop down to about 1500 and slowly make it'* way back down to regular idle. I beleive that is a tel tale sign of a clogged cat?
is it doing this while your foot is still on the gas?!?
i would think that a clogged cat would cause it to drop revs quicker than normal.
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Old 02-28-2005, 10:31 PM   #6
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A clogged cat will not be evident at idle. Only under throttle. It would also tend to overheat the car.
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Old 02-28-2005, 10:50 PM   #7
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No, not with my foot on the gas. That would not be good.

I was just asking because I'm replacing the cat. sometime this week.

Click me!

Now, assuming I'm not a complete idiot the yellow cirlce is my EGR valve and the red circle is the vacuum distro block? I'll get on it for this weekend.
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Old 03-01-2005, 07:11 AM   #8
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Yep, that is correct. Pull off all the lines, and make sure they are all intact, not rusted, not deteriorated, etc.. Some of my metal lines have some surface rust, so it is possible that you may have some rust holes. Be sure to check all those out. Also make sure none of the nipples on the distribution block are broken [mine had one], because that'll bite you in the *** too.


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Old 03-01-2005, 06:25 PM   #9
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I took a good look at it to familiarize myself with it, and this is what I noticed.

Distro block
1 2
[===] 5
3 4

1 - Goes up to the firewall where it is divided, one line into the firewall (for CC and the HVAC), and the other swings back around and connects to a device directly under the intake accordian hose. What is that?

2 - Capped off, no use.

3 - This went to some device lower in the engine bay I think called the trans vac? Not sure off its function.

4 - To the fuel pressure regulator. I noticed mine was made by Bosch.

5 - There is a fifth one that goes to something by the intake snorkel...it says canister on the diagram, and that apparently goes to the gas tank.

Now...I noticed besides the hose there were lots of L-connector type things and rubber boots connecting the metal lines to the devices. So besides tubing/hose what else do I need to buy? And if there is a metal one that is rusted through what should I do? Replace it with rubber? And lastly, will I need to buy different diameters of hose? I noticed some were smaller and some bigger.

thanks alot...my knowledge slowly builds....

edit: I also noticed it was running considerably better today...couldn't see the shaking, but I could still feel it.
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Old 03-01-2005, 07:39 PM   #10
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What I did was grabbed a sample hose and went into the Auto Parts store. Told 'em I wanted whatever they had left of this diameter.. and they hooked me up. I am a VERY good customer at Autozone, so they usually cut me a deal. The hoses of different diameter, need to be replaced with that diameter hose. You cannot interchange diameters. If the metal lines are rusted through you should replace them with metal lines [you get to have the joy of bending them yourself]. But, a rubber line would serve the purpose, just not look as pretty. The metal lines have a clamp or two on the block somewhere.. just un-bolt 'em and remove. You will see where the rubber lines are.. if they are original they will fall apart in your hands.

Your diagram is correct, except the 'trans vac' is the Vacuum Modulator .

Your FPR is NOT on the distro block, however it is right buy it.. and being made my Bosch isn't bad.. just some tune up items don't last a while in GM cars.

The line going to the Charcoal Canister [one of the metal lines, joined with the Vacuum Modulator line] does eventually go to the Fuel Tank, along with the PCV Valve.


-justin
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