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Discussion Starter #1
Hi all,
Please help me to diagnose the following.

I have Honda Accord 2006 2.4L with 165,000 km on it (100K miles).
The engine RPM drops to 500 when I am stopping. The rotation drop happens at the end of stopping and is very short - a couple of seconds. After that the rotation comes back to normal 650-700 rpm.

A bit of history that might be related to the issue.
Yesterday I performed B124 service which includes valve clearance check/adjustment, spark plugs and air filter replacement. The intake valves were within the specifications and I left them alone. The exhaust valves were a bit tight barely passing 0.01” feeler gauge so I loosen them to 0.012” as per specs. One of the work lights my son and I used was connected to the car battery and we likely depleted it as in the morning I had to jump start the car. I did not run the car the same evening when we completed the work as RVT I used for mating surfaces under valve cover gasket required 24 hours.
During driving the car after the jump start I noticed that engine RPM drops to 500 when I was stopping. The rotation drop happened at the end of stopping and was very short - a couple of seconds. After that the rotation came back to normal 650-700 rpm. The engine coolant was in the normal temperature range. The engine runs smoothly, may be even smoother than it was before I did the service.
While testing the car I noticed similar drop in RPM when I shifted from Neutral to Drive.

What could be the reason for this RPM drop and how can I troubleshoot?

Thank you in advance
 

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Elvira - the car
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3,496 Posts
Welcome to the forum fixAnddrive.

Off the top of my head sounds like a vacuum leak somewhere.

Are you sure all the spark plugs were snugged down?

Is the air intake tube correctly positioned? Was the hose clamp tightened enough? Did it slip?

Also check to make sure the air intake hose didn't crack or split when you removed it.

Try those first then we can get into the expensive stuff.
 

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Discussion Starter #3
Thank you, Mike!
I checked all possible air tubes/hoses, their clamps and connectors. Everything seemed normal. I used a piece of a pipe as a stethoscope to find any obvious hissing sounds. I could not detect anything. I let the engine to warm up and initially was able to reproduce the slight RPM drop. After that I drove around for a few minutes and could not reproduce it any more. Yesterday the issue was reproducible even after 10-15 minutes drive.
Can the possible issue be a weak battery and it is due for replacement?
 

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Elvira - the car
Joined
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3,496 Posts
Thank you, Mike!
I checked all possible air tubes/hoses, their clamps and connectors. Everything seemed normal. I used a piece of a pipe as a stethoscope to find any obvious hissing sounds. I could not detect anything. I let the engine to warm up and initially was able to reproduce the slight RPM drop. After that I drove around for a few minutes and could not reproduce it any more. Yesterday the issue was reproducible even after 10-15 minutes drive.
Can the possible issue be a weak battery and it is due for replacement?
yes. all your sensors may have been relearning and the ECU may have kept the IACV open longer than it should. How old is the battery?

http://www.driveaccord.net/forums/86-9th-generation/316890-new-battery-parasitic-draw-test.html

This is what I found about my battery and why I changed it.

Not saying you have a parasitic draw just that the battery condition IS critical.
 

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Discussion Starter #5
The battery is 5 years old. It is not OEM. OEM one died after 4 years in use.
I can't see the specs of the battery but it should be about 40 Ah capacity, 36 Ah minimum. The fact that we drained the battery after running 50 Watt light for about 4 hours worries me. 50w / 12 V is only 4.16 A. This should account for 16.7 Ah of used charge after 4 hours. Not a good sign.
 
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