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Old 11-07-2012, 01:34 PM   #1
pnasty101
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Question 2000 3.1v6 idle all over the place

I have a 2000 malibu 3.1 v6 base.

My idle is all over the place. Normally it sits around 800rpm, however after anytime i unplug the sensors/have to take off the top intake manifold piece, the idle will then be all over the place. It's random.

Yesterday when started first thing in the morning it was 2000rpm. Drove to work, put it in park and it shot up to 3500rpm. It was idling so high that my brakes barely stopped the vehicle.

Then today it started up at 1200rpm. I've noticed after i drive it home from work (hour drive), the idle will be lower or closer to where its supposed to be.

I replaced me lower intake manifold gaskets about 1 year a go and experienced this then, but it went away. It seems like everytime i unplug the sensors it comes back and it just takes a while to work its way out. Maybe a buggy sensor? When this originally happened i replaced the MAF with no difference. Last night I unplugged each sensor I had disconnected to service my fuel injectors, and I found no difference in idle for any. Gakets on upper intake minfold are 1 years old.

I did notice that the front valve cover breather tube has a vacuum on it, and when i block it with my thumb, the idle decreases about 100rpm or so. I should also point out that the rear valve cover breather hose (that lead to ths air intake) is loose and not forming an air tight seal. However I wouldn't think this would matter since it's just leading to the air intake tube and has been like this before this started happening

Maybe i need to disconnect and reconnect my battery to reset everything? Since you are supposed to disconnect the battery before performing and maintenance. Thoughts?

Throttle body and sensors were cleaned 1 year ago. Fuel injector 0-rings just replaced last Sunday, hence i've had the problem since.
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Old 11-07-2012, 03:11 PM   #2
DrivenDaily
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Default Re: 2000 3.1v6 idle all over the place

Sounds like it's sucking too much air and the PCM is adding fuel. Any new work is always suspect wen things happen immediately afterward.
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Old 11-07-2012, 04:55 PM   #3
pnasty101
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Default Re: 2000 3.1v6 idle all over the place

Quote:
Originally Posted by DrivenDaily View Post
Sounds like it's sucking too much air and the PCM is adding fuel. Any new work is always suspect wen things happen immediately afterward.
I replaced all fuel injector and fuel line o-rings. No leaks so that's good, as one of my injectors was leaking pretty bad before. However now I believe I have a noisy injector, it clicks sometimes at initial startup then goes away.

What i'm wondering is, i guess its possible there's a leak where the upper intake manifold bolds down, but i kind of doubt it because i made sure nothing could have obstructed it, and it went on very smoothly with no trouble.

*I disconnected the battery for probably an hour tonight and then reconnected it. Afterwards the car would initially go up to 1200rpm, and then it would settle to 800rpm after fluctuating a bit.
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Old 11-07-2012, 08:11 PM   #4
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Default Re: 2000 3.1v6 idle all over the place

My PCV fitting leaked under the throttle cable bracket. I had a similar problem until I replaced it - then the idle settled down to the proper value.

Part was something like $8 at the Chevy dealership.

RwP
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Addendum: Rest in peace. Surge tank blew, motor overheated, I think she's lived a long and useful life.
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Old 11-08-2012, 09:14 AM   #5
pnasty101
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Default Re: 2000 3.1v6 idle all over the place

I noticed that the small u-shaped hose coming off the vapor canister purge valve by the throttle body is compressed. It seems like the vacuum is enough to suck in and compress the deteriorated hose.

Thoughts? The other side of the line connects to the front valve cover/pcv valve on end. I'm guessing a dealer only part as i'm taking it that u-bend will not fair well with plain straight hose.
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Old 11-08-2012, 04:40 PM   #6
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Default Re: 2000 3.1v6 idle all over the place

Here's a picture so you guys can see exactly what i'm talking about.

#1 is the valve in the front valve cover. When i take this out and put my thumb over the valve, the rpms will go down 100rpm or so

#2 is the samll ushaped hose that i was talking about in my post above this one. It's deteriated a bit i'd say and is getting restricted from the vacuum.

#3 is the wires i believe that lead to the air temp sensor. Don't know what happened but they definitely look like they've been re-spliced.

#4 is the rear valve cover hose to the intake tube. This tube is very loose on the valve cover. Maybe this could be part of the problem since the air getting sucked in is not metered by the MAF.


For the last few days its been consistent; starts up cold and stays at 1200-1400rpm. Get to the destination, put it in Park, it and it will settle down to the correct idle. If it's still a little high after i get to the desination, if i turn off and restart my car it the idle will come down to where it should be.

Which tube are yee talked about under the TB?

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Old 11-09-2012, 08:12 AM   #7
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Default Re: 2000 3.1v6 idle all over the place

Quote:
Originally Posted by pnasty101 View Post
Here's a picture so you guys can see exactly what i'm talking about.

#1 is the valve in the front valve cover. When i take this out and put my thumb over the valve, the rpms will go down 100rpm or so

#2 is the samll ushaped hose that i was talking about in my post above this one. It's deteriated a bit i'd say and is getting restricted from the vacuum.

#3 is the wires i believe that lead to the air temp sensor. Don't know what happened but they definitely look like they've been re-spliced.

#4 is the rear valve cover hose to the intake tube. This tube is very loose on the valve cover. Maybe this could be part of the problem since the air getting sucked in is not metered by the MAF.


For the last few days its been consistent; starts up cold and stays at 1200-1400rpm. Get to the destination, put it in Park, it and it will settle down to the correct idle. If it's still a little high after i get to the desination, if i turn off and restart my car it the idle will come down to where it should be.

Which tube are yee talked about under the TB?

See that bracket under the hose you've labeled 4? There's a fitting into the upper intake that was in pieces on my car. It's part of the hose that goes from the PCV valve (which you've labeled 1) to the rear fitting. That's the part that's about $8.

RwP
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335K miles on original motor and tranny (only motor work 2 x LIM replacement), Monroe SensaTrac struts front and back (new at approx. 300K miles), and Alero discs in back. LS fogs added with custom wiring. HID high beams, HIR low and halogen fogs. Raybestos Pro Grade front rotors and Bendix D747 ceramic pads on front.

Addendum: Rest in peace. Surge tank blew, motor overheated, I think she's lived a long and useful life.
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