2003 Montana idles high

[MEDEL514]

I've read the other posts On here that it had the same problem. I changed the idle control valve and Reset the ECU by disconnecting the battery. The Van still does the same high idle after warm up usually around 2500 rpm. I also thoroughly look for vacuum leaks and found nothing. I unplugged the throttle position sensor thinking that might have an effect but no change nothing changed.

What else have I missed what else you think can be done to solve this problem. Any help is greatly appreciated thanks.

[carriedi]

is your check engine light on?

Are there any codes to give you a hit on what to look for?

Usually high idle like what you have is a vacuum leak. A scanner could look at your fuel trims and see if the engine is adding air because your O2 sensor is reading too lean and adds fuel. Too much air and too much fuel will make the engine speed up.

the mass airflow, map sensor and the throttle position all tell the computer what to do so the computer sends the right fuel and spark to make your engine run it's best. The O2 sensor overrides all that because it tells the computer if you're polluting the whole earth with your exhaust. (slightly exaggerating). So, if the O2 sensor says to much air it tells the computer add fuel to give the 14.7 ratio it needs.

How is your engine running? When you put it in gear does the idle drop down? Is the engine running smoothly? What did you do to look for vacuum leaks? Did you check the egr valve and the canister purge valve to see if they are sticking open?

but, a scanner would help out a lot to see what the engine is doing

[Guest]

So weird issue, The next day after changing that IAC valve, I plan to go have the air fuel read and any other codes. I drove it to my local auto store and the Van works fine idled perfectly in everything, So there is nothing for us to check I thought the problem had somehow fixed itself. Well the following day I was going to take it to work and as soon as I started it it idled at 1500 which is about 600 rpm higher, And as it warmed up crept up to 2500. So the problem is back. I will now take this back to the auto store and hopefully we can find something wrong and I can have a way forward.

[MEDEL514]

So weird issue, The next day after changing that IAC valve, I plan to go have the air fuel read and any other codes. I drove it to my local auto store and the Van works fine idled perfectly in everything, So there is nothing for us to check I thought the problem had somehow fixed itself. Well the following day I was going to take it to work and as soon as I started it it idled at 1500 which is about 600 rpm higher, And as it warmed up crept up to 2500. So the problem is back. I will now take this back to the auto store and hopefully we can find something wrong and I can have a way forward.

[carriedi]

Your TPS can cause a high idle. See if the idle voltage is too high. Should be .4V or under. If it goes over 1.0V it will affect the idle.

PCM is also a common problem.

Bcm sending false information to the ecm can also affect the idle. Look for ac request when you don't have the AC or defrost on.

Look at your IAC signals. you have two signals iac-a iac-b. What are they doing while the engine is idling high? Use the scanner to do an IAC test and raise and lower the idle speed.

Doesn't sound like it's a vacuum leak because the leak would have still been there after you changed the IAC. Since you changed the IAC and it was good foe a while I would look at something else that affects the computer that electrical.

watch the data stream while moving the wire harness to the TPS, IAC, MAF or other things that may have a bad connection and affect the idle circuit.

see if your vehicle has a power steering switch. Check if there is power steering fluid coming through the switch into the wire harness connector.

without a graphing scanner to watch while you check circuits and wiggle the harness it may be tough. You'll have to hope the idle will change so that you can notice a change. they sell connectors with pigtails to splice into the harness for broken wires that may go back as far as 12" away from the connector.

[MEDEL514]

So the symptoms have changed slightly. Now it will idle ok when I first start the engine, but then it will idle high when I go to drive and put a load on the engine. I'll pull over, shut down and restart the van, and the idle will be fine again...until I go to drive off and it idles poorly while driving. I'm at a lost, about ready to take it to a mechanic...

[carriedi]

A lot of driveability problems need to have a scanner hooked up to see what's going on when it's going on. What to look for on the scanner like idle rpm. Does the vehicle have a pid (parameter identification) for desired idle? Dies the desired idle match the actual idle? If the desired idle is too high the the computer is reacting to some other pid that that is out of the norm.

The computer changes the Idle Air Control changes according to load on the engine. When the transmission go into gear. When the AC comes on. When the radiator fan turns on. I have seen it when the BCM sent bad information to the PCM and told the PCM that the AC compressor was on so turn up the IAC but the AC wasn't on so the up. It was found on the PCM pid for the ac compressor signal. It was going on and off on the graph. The ac on the dash was turned off and the compressor was not powering up. Without a scanner I don't think anyone would figure that out. You would think that the ac is turned off and it isn't coming on at the compressor so why would you think that would be the problem?

We use a snap on scanner that lets us look at a lot of pids and we can let it run and drive it over time and then we can save the information and open up page to view all the pids as graphs. When we see the idle get high we can mark that spot and then follow that point down through all the other pids to see what else changed at the same time. that may give us a clue to what happened to cause the PCM to want to change the idle.

Have you checked to see if any codes have been stored

[MEDEL514]

So I took the car to mechanic today and they said that I have an EGR valve leak, a lower intake manifold gasket leak, and a throttle body leak but the throttle body is no good and will have to be changed. How do throttle bodies just go bad it was not damage he but he said it had to be changed.

[carriedi]

ask them how did they find the leaks? What makes them think the throttle body is bad?

Throttle bodies go bad all the time. Ok, not all the time, but it isn't uncommon. They have a lot of circuitry in them, circuits that are tied to movement. those circuits can wear out, get contaminated or just go bad. Just like computers go bad. But when these go bad they will set a code. Or they will show up on the scanner not responding like they should. You can look at the position sensors and see if they are working correctly and matching each other, one moving one way and the other moving the other way. Or you can command the idle to change and see if it responds. You should have the leaks fixed first and then test. If it has codes that the sensors inside don't work right then the idle test doesn't make any difference. Get a print out of all the codes your car had. The numbers. If the code for the throttle body is because the idle cannot be brought down to the desired idle, if you have vacuum leaks that make it artificially raise the idle that could set a code. Once the leaks are fixed that's when you see if the throttle body is good or not.

[MEDEL514]

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....

[carriedi]

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...

[MEDEL514]

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.