High idle only before engine reaches full operating temperature

Tiny
BEN LEE
  • MEMBER
  • 2001 HONDA ACCORD
  • 2.3L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
I've been trying to solve some idle issues on my car for several weeks now. At first I was getting a surging idle that would up to 2500 or so rpm and back down over and over again, and when it wasn't surging it would idle very high around 1500 rpm or so. As soon as the car would reach full operating temp (usually after 15 minutes of driving, but sometimes less), it would drop drop down to a normal idle around 700 rpm and then run perfectly for the rest of the trip.

I performed a lot of diagnostics and some repairs (listed below) and thought I had it fixed after replacing the MAP sensor as the last step, but after less than a week of the engine running normal, some issues came back, but not the surging. Currently it is just idling high at about 1200 to 1300 rpm, but it seems to take only 5 minutes or so for the car to start running at normal rpm. It will also have an occational jump or dip in rpm while driving (not at idle), but it is very quick and it does not pulse up and down at all. For instance, I could be going 40mph on a surface street and at 2000 rpm and I'll feel a sudden/small jump and see the rpm needle go up just 100 or 200 rpm, and then if I watch it for a few seconds it will usually jump back down again. It is a very quick jump and it stays in the spot that it jumped to for at least 10 seconds, rather than continually jumping up and down. This symptom is just occasional, not continuous, and stops after 5 or 10 minutes of driving cold. Also, I'm in Southern California, and the coldest weather I drive in is 45 degrees or so, but these symptoms can also occur when it is 70 degrees out when the car is started up cold.

Here's what I've done already:

-checked for vacuum leaks many times, originally found none after several attempts, but after intake removal I found a small one where the intake air duct connects to the throttle body and then tightened the hose clamp and corrected it. I'm not sure if this leak was there all along, but I may have just caused it by not connected the air duct well enough after putting the intake back together

-removed the intake and thoroughly cleaned the carbon inside, including the egr passages, the throttle body bore and plate, and the idle air control valve

-replaced the PCV valve

-tested the EGR valve. Disconnected it, ran the engine, put 12 volts to it to manually activate it and the engine stalled (as it should), so it seems to be fine

-tested the Idle air control valve by checking the vacuum going to it, as well as checking the vacuum after disconnecting the electrical connector while at idle. Seems to be correct, and the voltage and continuity at the IACV pins is correct

-bled air from the cooling system

-checked the air filter and it was fairly clean since it had been replaced not long ago, but I went ahead and knocked some excess dirt out of it

-got a MAP sensor trouble code and tested the MAP sensor and all the voltages/function tested correct. I replaced the MAP sensor anyway since the trouble code was all I had to go on at this point, and after that the car ran very smooth and at the correct idle from a cold start.

At this point I thought I had it fixed, but less than a week later the high idle that I described above started happening. It is still running much better than it was before all these repairs were done, but it is not running like it should and is not running like it did right after I replaced the MAP sensor about a week ago.

Thanks for any input and suggestions that you may have!
Thursday, December 3rd, 2015 AT 9:03 AM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,124 POSTS
A loping idle is usually the result of a bad IAC. Did you check it for resistance?
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Monday, December 7th, 2015 AT 6:54 PM
Tiny
BEN LEE
  • MEMBER
  • 66 POSTS
I did several tests on the idle air control valve and I think one of them was for resistance, but that was a week or two ago, so I don't remember the exact results, but I do know that the testing I did showed that it was within specs.
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Tuesday, December 8th, 2015 AT 2:09 PM
Tiny
BEN LEE
  • MEMBER
  • 66 POSTS
I don't see any words in your last response.
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Wednesday, December 9th, 2015 AT 1:39 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,124 POSTS
Do you have access to a scanner that you can read real time data from? I would like to know what the coolant temp sensor is signaling to the computer.
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Wednesday, December 9th, 2015 AT 4:30 PM
Tiny
BEN LEE
  • MEMBER
  • 66 POSTS
The scanner I have is a low end one, but it does read some live data, and I'm pretty sure the coolant temp is something that it will read. I'll take a look at that and get back to you. Thanks
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Thursday, December 10th, 2015 AT 7:06 AM

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