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Old 01-26-2015, 08:41 PM   #1
dadooishome
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2004 Aveo very high idle

Got a 2004 Aveo last summer with 61k miles. Did the timing belt kit and tune up so it ran fine. Then it started randomly idling at 2200 rpm. Bought a new Idle Air Control (IAC) unit and it worked fine... for a few days, then the idle went to 3000. Disconnected the Throttle Position Sensor (TPS), it ran normal a couple days... then back to 3000. Decided it might be getting too much air from the EGR, so I disconnected the entire EGR (and plugged the ends) and it ran normal. So I put in a used EGR..., but it made no difference.

If I goose the throttle to 4000 then hold the butterfly closed, the idle drops down to 1100 for a second, then bounces back to 3000. Where is it getting all that extra air? In gears 3-5 under load it will only pull 2200 rpm, but when I put in the clutch.... 3000. So I just can't drive it.

The problem does seem somewhat temperature related because after an hour or so it sometimes does drop down to 1200 which is still too high.

I am completely baffled by this thing. The only OBDII code is the ''engine rpm does not match throttle position". How can it get that much air behind the throttle butterfly with the electrical connections for the: IAC, TPS, and EGR all disconnected? HELP!
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Old 01-28-2015, 12:54 PM   #2
j cAT
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Re: 2004 Aveo very high idle

Quote:
Originally Posted by dadooishome View Post
Got a 2004 Aveo last summer with 61k miles. Did the timing belt kit and tune up so it ran fine. Then it started randomly idling at 2200 rpm. Bought a new Idle Air Control (IAC) unit and it worked fine... for a few days, then the idle went to 3000. Disconnected the Throttle Position Sensor (TPS), it ran normal a couple days... then back to 3000. Decided it might be getting too much air from the EGR, so I disconnected the entire EGR (and plugged the ends) and it ran normal. So I put in a used EGR..., but it made no difference.

If I goose the throttle to 4000 then hold the butterfly closed, the idle drops down to 1100 for a second, then bounces back to 3000. Where is it getting all that extra air? In gears 3-5 under load it will only pull 2200 rpm, but when I put in the clutch.... 3000. So I just can't drive it.

The problem does seem somewhat temperature related because after an hour or so it sometimes does drop down to 1200 which is still too high.

I am completely baffled by this thing. The only OBDII code is the ''engine rpm does not match throttle position". How can it get that much air behind the throttle butterfly with the electrical connections for the: IAC, TPS, and EGR all disconnected? HELP!
with the throttle plate closed and 3K RPM there must be a vacuum leak.

use a vacuum gauge and with this taped into the intake see if you can make the gauge react by using propane to locate the leak... this set up is using a small torch with a 4 ft hose on the tip open the valve so just a small amount of propane comes out.. then use the hose tip/end to probe for leaks... you will see the vacuum and rpm shift when the gas enters the engine ... too much gas will make it harder to find leaks.

this is the best method than using spray products//safer..
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Old 01-29-2015, 12:54 PM   #3
dadooishome
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Re: 2004 Aveo very high idle

j cAT,
Okay I will give the propane a try.
This is one strange engine design. I found that the EGR is bolted directly to the lower block on the *intake* side of the engine. How does it get exhaust gas from that location? There must be some odd internal plumbing to do that.
Also, there is a 1"OD hose coming off the valve cover with a T connection for the normal PCV hose. The other section of the 1" hose goes to the intake manifold behind the throttle butterfly. Could this hose be providing all the extra air?
Everything is a bit tight to work on... I don't have small Korean hands either.
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Old 01-29-2015, 01:10 PM   #4
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Re: 2004 Aveo very high idle

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Originally Posted by dadooishome View Post
j cAT,
Okay I will give the propane a try.
This is one strange engine design. I found that the EGR is bolted directly to the lower block on the *intake* side of the engine. How does it get exhaust gas from that location? There must be some odd internal plumbing to do that.
Also, there is a 1"OD hose coming off the valve cover with a T connection for the normal PCV hose. The other section of the 1" hose goes to the intake manifold behind the throttle butterfly. Could this hose be providing all the extra air?
Everything is a bit tight to work on... I don't have small Korean hands either.
PCV system hoses are a common leak item. the intake area and the components mounted are suspected ..propane works good .. you do have a very large leak..

at idle the throttle plate need be closed. stuck open EGR will cause the engine to stall and run poorly due to reduced oxygen into the intake. then though the egr power head could have a vacuum leak..
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Old 04-01-2015, 09:07 PM   #5
Tinaprincess25
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Re: 2004 Aveo very high idle

Hi my name is Christina and I to have the same problem with my 2004 chevy aveo I changed the tps and it still ran high idle I would like to know how to fix it
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Old 04-02-2015, 07:41 AM   #6
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Re: 2004 Aveo very high idle

It has been too cold to work on this the past month or two.
I am now fairly certain the intake manifold has a bad gasket somewhere. I have literally checked everything else going into the manifold. To achieve an extra 1200-2200 rpm it takes about a 1/2" diameter air leak. So this weekend I am going to pull off the manifold. It is a large one-piece plastic unit and very difficult to access, probably 2-3 hours each way . I will post again when finished.
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Old 04-20-2015, 07:08 PM   #7
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Re: 2004 Aveo very high idle

Just wasted more than 10 hours replacing the intake manifold gaskets. There was a 1" gasket section missing from 3 of the 4 intake runners. But I still have the exact same problem.

While checking for the air leak I disconnected the air hose on the throttle body while the engine was running with the high idle of 2500 rpm. I noticed it did not make any difference if the electrical connection was on or off the idle control valve. The intake air hole for the idle control in at the 12:00 position of the throttle body. If I covered the hole it went to 800 rpm. So what I learned was:
1. the high idle *is* completely random (1200/1500/3200 rpm. hot/cold)
2. it does this random idle with or without power to the idle control valve
Therefore each time I thought I had fixed the problem, it was actually just the idle control deciding to run normally.... for awhile.

By the way, the *first* thing I replaced was the idle control valve.
I am now going get my meter and check the inputs to the valve.
Then decide if I have a bad new part, or bad wiring. I will post again.
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Old 04-25-2015, 04:22 PM   #8
dadooishome
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Re: 2004 Aveo very high idle

Okay, I found out *all* the extra air for the high idle is coming through the idle bypass circuit. The brand new idle control valve is doing something extremely sinister- it randomly decides what speed the idle should be, and it does this even when the 4 pin plug is disconnected!!! Grrrr.

So each time I disconnected a component (EGR, TPS, PCV) it would go to a normal idle for a few minutes, hours, even days.... then go back to a completely random high idle. (though it is a bit temperature related)


Therefore I plugged the idle hole in front of the throttle butterfly valve- thus taking the entire idle circuit completely out of the equation. Now it never idles above 800 rpm. So I can now drive the car, but not very well when it is still cold.

I took my analog meter to check the 4 wire inputs to the idle control valve. There were three things which are very strange:
1) none of the 4 wires is a ground
2) with the engine off, each of the 4 wires measure about 20k ohms
3) when the engine is warm, all 4 of the wires would "pulse" between 1v and 11v at a one second interval

So is this the normal input on the 4 wires? HELP!

Problem Solved!!!

Finally resolved this issue by buying a used throttle body (which included the TPS and IAC) for $45.
http://car-part.com/

Found out both of the new IACs I installed were bad and had failed in the same manner as the original IAC.
What are the odds of that happening?
So I chased this problem for 6 months.... when the first component I replaced should have fixed it.

Lesson learned: the $12.50 Amazon/Made in China IAC was not much of a bargain.
Thanks for all the help.

Last edited by dadooishome; 06-05-2015 at 01:42 PM. Reason: Problem solved!
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