engine RPM goes up and down at traffic light

HONDA ODYSSEY
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ERIC OU
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My van is a 2003. It was running smoothly until two weeks ago after an oil change at a garage. Right after the oil change, when I stopped at a traffic light, the engine rpm's went up and down between 700 rpm's and 900 rpm's. The drive gear (shift) is on drive. If I shift the driving gear to parking or neutral, the engine would run fine. After fifteen minutes of driving, the symptom would go away. I brought the minivan back to the garage. They said there was a vacuum leak and fixed the problem. However, the problem is still there.

I took the minivan to a Honda dealer. At first a mechanic said that he could not find anything wrong. There was no error code. Then he said the air control valve is bad and replaced it. However, the problem did not go anywhere, even worse. Now, no matter long I drive the minivan, the symptom stays on.

But if I turn the steering wheel to either right or left for some degree while the driving gear (shift) is on drive (of course I put my foot on the brake pedal), then the engine would run smoothly.

What could be wrong?

Thanks
Dec 7, 2006 at 3:59 PM
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BRUCE HUNT
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I would sense that turning the wheel right or left puts a slight strain on the engine and it must compensate for this by supplying more fuel. I would venture to say that if you apply a bit of gas while sitting there it goes away as well.

What other work has been done to the vehicle recently?
Dec 7, 2006 at 11:42 PM
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ERIC OU
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Bruce,

I applied a little gas and let the engine rev go above 1000 rpm's, the problem went away. I did not do anything on the minivan recently.

Thank you.
Dec 8, 2006 at 12:22 PM
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BRUCE HUNT
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This sounds like a vacuum leak. Check hoses, idle air control valve can be taken off and cleaned. The next thing I would do after the check of the hoses though is to check the cooling system for being full and make sure you purge the air out of the system through the bleeder valve.
Dec 8, 2006 at 6:42 PM
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ERIC OU
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Bruce,

You are amazing! I checked hoses and found no problems. Then I opened the radiator cap (hope to release some air if any) and put it back. The problem is gone.

By the way, how is that related to the engine rev?

Thanks a lot!
Dec 9, 2006 at 11:13 AM
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BRUCE HUNT
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Air gets trapped in the system, little pockets get joined together and a pocket of air does not exactly reflect the temperature of the coolant. The sensors in the engine think it is one temperature but the air has another temperature and they send mixed signals to the computer. Then the computer requests more gas, then less gas, etc. Confusion!
Dec 9, 2006 at 4:55 PM
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AUBIERPH
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I just wanted thank you for this information and help. My wife was dropping several neighborhood children at school and the odyssey suddenly lurched forward. Fortunately, my wife successfully stopped the minivan with, what else, the brake, but not after sending a panic through all of the passengers. My wife arrived home in a panic, saying she barely made it home with van lurching and revving. After two hours of web research, I decided to get a new transmission. $3,000.00 to $4,000.00 from Jasper Transmission. Then, a friend said it may be the 'torque converter'. I did another search for 'revving' and stumbled across this information. I went outside, opened the radiator cap, a little bubble escaped like a tiny fart. I restarted the car and voila! the revving disappeared! Thank you so very much! Kenneth Garrison, Huntsville, Al.
Oct 13, 2014 at 8:26 AM
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ERIC6K
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Last night noticed that in park or while idling, rpms were fluctuationg wildly, engine revving up and down.
Is this serious or can i drive it for a while before checking it out?
No warning lights are coming on.
thank you!
Nov 20, 2018 at 10:57 AM (Merged)
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MERLIN2021
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Things you'll want to check are, The idle air control, it's on the side of the throttle body, the EGR for sticking open, And a possible vacuum leak...Get a can of spray gumout, start the car and spray around, pay attention to vacuum lines and manifold, if the idle changes, you found a leak. Poor mileage and these symtoms, I suspect a vacuum leak and or the need for a tune up!
Nov 20, 2018 at 10:57 AM (Merged)
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RICHARD SCHLAMP
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I have noticed in the last couple months that when I start the car it does not idle properly. It will set there and idle up and down like it is surging. I have checked and I do not believe it has an fuel filter so that problem is eliminated. I keep the air filter clean and change it 2 times per year and I do regular maint. Thank you richard
Nov 20, 2018 at 10:57 AM (Merged)
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KHLOW2008
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Hi richard ,

Thank you for the donation.

Actually it does has a fuel filter located in the fuel tank with the fuel pump but it is not the cause of the problem.

What you are experiencing is surging due to incorrect amount or air needed for idling and the PCM is trying to compensate.
Most likely cause is a dirty throttle body, idle adjust screw, Idle Air Control valve or clooged coolant hoses to the IAC and throttle body.

A good cleanup of the throttle body and IAC should solve the problem.
Nov 20, 2018 at 10:57 AM (Merged)
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2CPUID11
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When I started the car few days ago after using it last on August 10th 2011, the idle speed racing up and down when in park and neutral but ok at drive gear.I like to know what are the possible causes.I did not notice any engine light on.
Nov 20, 2018 at 10:57 AM (Merged)
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JACOBANDNICKOLAS
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It sounds like a bad idle air control valve. It is located on the throttle body. Check that. Also, check for vacuum leaks.
Nov 20, 2018 at 10:57 AM (Merged)