1999 Honda Civic Random idle surge on 2nd start only.

Tiny
MOTIVATESOMETHING
  • MEMBER
  • 1999 HONDA CIVIC
1999 Honda Civic 4 cyl Two Wheel Drive Automatic

I have a 1999 honda civic ex 2 door coupe. I changed the idle control valve, spark plugs, fuel pump, some vacuum lines, the pcv valve and hose, checked all lines for leaks, replaced the 02 sensor twice, readjusted the throttle position sensor (its in proper range with no glitches) new spark plug wires, cap and rotor, new injectors as well! And I STILL get a warm start, RANDOM, idle fluctuation, like the car cant determine the air fuel ratio for a minute, so the idle surges up/down until it finally settles. Also when this happens the car has a slight power loss when driving and the muffler gets louder. I put on a new header, catalytic converter, and stock exhaust on the car and STILL the problem exists. I have also cleaned the throttle body, the engine with seafoam a few times, I have adjusted the idle as my manual says and replaced the throttle body gasket with an oem honda one twice. I have bled the coolant system several times, in case air is causing the idle surge to no avail. The engine compression checks out fine as well. I have done all oil changes and transmission changes.

Im now thinking coolant temperature senor?(Although it seems to detect the temp just fine) or the pcm itself? Or my map sensor. Could the map sensor cause this intermittent idle surge? ('Ive cleaned it twice) sometimes it doesnt happen at all and the car will run and idle flawless. Never does this on a cold start though. I've dumped alot of money in so far. Any hope?
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Tuesday, October 12th, 2010 AT 5:20 PM

9 Replies

Tiny
F4I_GUY
  • EXPERT
I've seen a MAP sensor cause this. Unfortunately you need a scanner to read the MAP data PID.

Another possibility is that you dropped the IACV gasket when you re-installed it. Also, I'd run another shot of throttle body cleaner through the IACV port on the throttle body just to make sure it's clean.

If you do have access to a scanner please post your long term and short term fuel trims when the vehicle is acting up. Thank-you.
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Tuesday, October 12th, 2010 AT 6:38 PM
Tiny
MOTIVATESOMETHING
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Ok the fuel trims only go near -8 and + 8 never higher or lower even when its fluctuating. When the car is running fine. The fuel trims are the same. The map sensor is 8hg at idle and moves up as it should upon acceleration. I tested the tps and it reads the right voltage and goes up and down in voltage as it should. This is really annoying and complicated at this point.

My timing on the car is correct. Has new timing belt too as of 8 month ago.

Can an air leak only cause a fluctuating idle on a already warm car? That just doesnt seem right. Unless somethings getting hot and expanding? But it doesnt do it EVERY hot start so could it be random undetected misfires? But look at the first post, I have all new everything except coolant and map and throttle sensors. And I know these are crucial to idle as well. But would rather stop dumping money at this point unless its for sure.
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Friday, October 15th, 2010 AT 4:50 AM
Tiny
KHLOW2008
  • EXPERT
If you have not checked the valve clearances, get them checked/adjusted and retry.

Ensure coolant hoses to and from IAC are not clogged.
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Saturday, October 16th, 2010 AT 9:54 AM
Tiny
MOTIVATESOMETHING
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Ok I had my mechanic adjust the valves, the car is running quieter engine wise (it wasnt noisy to begin with really though) and the idle problem still persists. Now I hooked up my scanner DURING the event of the surging. Today the surging was worse than ever, it stayed in the 1500-1700 range going back and forth between the two. Took it 4 straight minutes of that, to return to a normal idle. With my scanner the long and short term fuel trims are still in their good range, both in the positive 2.0 range. Nowhere near out of their limits. All the sensors are increasing when the throttle is applied and they release smoothly as well. This is seeming like a ECU problem to me at this point ? I vacuum tested the car for leaks AGAIN and its rock solid. I have new vacuum lines so why wouldnt it be. How can I finally confirm its the ECU? Any tests I can do with the ECU?>?
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Thursday, October 28th, 2010 AT 6:49 PM
Tiny
KHLOW2008
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Did you check the coolant hoses to and from the IAC?
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Friday, October 29th, 2010 AT 9:13 AM
Tiny
MOTIVATESOMETHING
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Replaced the coolant hoses to iacv. Problem still exists. Brought the car to yet another mechanic. No air leaks. Could an ecu ONLY cause idle problems yet the car run flawless otherwise? Really baffled. Car is fully tuned up and runs great but still this warm start idle fluctuation exists.
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Wednesday, November 10th, 2010 AT 8:06 PM
Tiny
MOTIVATESOMETHING
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Power loss is gone since installation of yet ANOTHER iacv. Meaning the "new" one I had was bad. I replaced it under warranty but the idle problem is still there.
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Wednesday, November 10th, 2010 AT 8:09 PM
Tiny
KHLOW2008
  • EXPERT
When replacing the IAC, did you test the ports where the hoses are attached for clogging?

A bad ECU can cause surging but usually trouble codes would be triggerred. The only way to test the ECU would be to substitute it.
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Thursday, November 11th, 2010 AT 7:53 AM
Tiny
MOTIVATESOMETHING
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Yes there is flow in this ports. No clogging. Iacv is working well. No trouble codes ever. : ( When I hit my gas I hear a slight whistle sound I noticed today. Air leak I imagine. Possibly from throttle body? Even with a new gasket? (Oem) Do I need to seal the throttle body gasket with silicone?
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Thursday, November 11th, 2010 AT 11:26 AM

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