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So I spent the past couple evenings changing the lower intake manifold gasket, to include all new gaskets on the upper intake manifold, EGR, TB, etc.

And guess what, THE ENGINE STILL DOES THE HIGH IDLE!!!

WTF, I'm about ready to drive this off a bridge....


   
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Location: Oregon
did you ever get the codes that the shop found when they looked at your car?

Did they look at the IAC value when idling at 2500 rpm? Was it zero?

If the IAC reads zero, that means that the computer has told the iac to reduce the idle but the iac cannot go any less. So, you look at the wiring to the iac, the reading at the oxygen sensors, fuel trims, EGR position, MAF reading...

did you ever ask the shop about how they found the vacuum leaks they found? Propane? Smoke test? Ultra sonic leak detector? Can you hear it just by listening to the engine?

High idle that is being caused by the computer is usually because the computer is reacting to the oxygen sensor reading. If it shows a lean exhaust from too much air in the mix it will give it more gas to bring the exhaust to show a 14.7 to 1 fuel ratio. (or similar reading). So, with more air (vacuum leak) and more fuel (computer) the idle has to go up. looking at the data stream on a scanner, you can see what is the computer is doing and what may be the reason it is doing what it is doing.

Guessing and replacing parts my get more expensive than having shop diagnosing and fixing the problem. But, like I said before, why does a shop recommend their coarse of action? If they find something wrong, how did they find it? What is the repair? Are there any codes stored in the computer? Need information...


   
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The shop said they found all the leaks through a smoke test. I spoke with the mechanic that did the smoke test and he said the smoke was very obvious at the throttle body IGR and especially under the intake manifold. He said he couldn't see exactly where it was coming from but he did say he saw the smoke coming from underneath the intake manifold. At this point I'm still convinced it's something electronic, But I don't believe they put the scanner on it.


   
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the scanner is one of the first things you should look at. How can you tell if the iac is working or not? Is the computer running the idle up or is the computer trying to turn the idle down and it can't? Look to see if there are any codes that could point you in a direction.

smoke test: intake shouldn't have any smoke, under the intake shouldn't have any smoke. EGR, you egr valve should be electric so, no smoke. Throttle body will have some smoke at the throttle shaft.

if there are leaks found with a smoke machine you can see where and how big the leak is. Where on the intake? Intake gasket? Under the intake? did they say what is under the intake that could be leaking smoke? Crack in the intake manifold? Where on the egr valve? the egr gasket? Is the egr valve stuck open and the smoke is going out the exhaust?

When you took it to the shop what did you tell them to do? I have people come in all the time and tell me what they want me to do on their car. Then I have to tell them I can do what you want but if you tell me what is the problem with your car is, maybe I can diagnose the problem instead of doing the test you're asking for. Now, maybe they are right and there is a problem with what they want checked. What's bad about that is if i just do the test they ask for, I may not find anything and they take the car with the problem still there.

If I had a customer ask us to check for a vacuum leak that's totally different than asking to find out why I have a high idle. High idle problem would be scanner first and maybe propane second. Watching the scanner values while I run the propane wand around where a vacuum leak might be. Watching the O2 sensor, fuel trims and idle rpm (iac)


   
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I took it to the shop for the high idle issue I didn't ask them to perform any specific test or anything, I just asked him to diagnose the car in see what was wrong and to tell me if the car was worth fixing. I let him know that I was gonna be selling it soon and didn't wanna put a lot of money into it but if it was something that could be fixed easily, then I would like to get it running properly. He quoted me 500 to $600 for this repair, and yet also offered me 750 cash on the spot to by the Van from me and he would fix it and sell it. I don't know if he hooked up an engine scanner nor do I know if it revealed anything. His shop was closed Friday evening and doesn't open till Monday, I'll be calling him back then to see what else was done for diagnosis.


   
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that sounds like a good idea. after they tell you what they did to find out what is going on with your van, tell them what you fixed and why do they think it would still be acting up.

ask what was the iac reading at idle when the idle is 2500 rpm? If it's zero then look at the wiring for the iac.


   
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Just an update to this thread. I'm still dealing with the high idle issue so far I've change the intake manifold gasket seals EGR gasket, And I've also swapped out numerous idle air control valves, throttle body position sensors, 2 different throttle bodies, 3 mass airflow sensors, and no codes come up when its running high. A guy I know is bringing someone who supposedly knows GM electronics pretty well so hopefully we can figure out more this weekend but we're thinking maybe its the engine computer. I will post updates later.


   
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I hope the person that the person you have coming to look at it can figure out what's going on. Then let us know what you find out and what it takes to fix it. I don't know if you ever had it on a scanner to watch the data the computer is using when it's acting up but I don't know how you can figure out what happening without one. PCM is always a possibility.


   
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