Idle air control valve or something else?

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For some time on my 02 Accord, I've noticed this intermittent issue when fully warmed up. When idling at a stop light, the RPM's drop below the tick mark below 1000, which I believe is 500. The engine then makes a slight chugging noise and idles not so smooth. It's more pronounced when the car is in park. Turning on an accessory like the headlights or A/C quickly brings RPMs back up to 750-ish again and all's normal. Car never stalls, accelerates fine when under load and otherwise runs great. No CEL is present and no overheating. Cold starts are normal at 1250-1500 RPMs. The idle doesn't bounce around like Honda's typically do when the IACV is messed up so I'm not sure if that's the issue. Things done so far: -Cleaned throttle body -Fresh oil change -ATF drain & fill -New OEM front engine mount (old one was cracked) -No apparent vacuum leaks -New air filter -New NGK spark plug wires -New OEM cap & rotor -NGK Platinum spark plugs ~2 yrs old. Properly gapped and tightened. -Bottle of Techron fuel system cleaner My coolant is about 7 yrs old. The level's good and there are no leaks but I'm wondering if there's air in the system after all these years. Eric the Car Guy says coolant's the first place to check for Honda idle issues. I'm going to bleed the system out and see what happens. What do you guys think?
 
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Quit part swapping and bring it to someone with a lab scope.
 
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M
Originally Posted By: KingCake
Quit part swapping and bring it to someone with a lab scope.
not sure I'd call an oil change and a tune up parts swapping. Clean iac valve, make sure batt terminals are clean and tight. I'm going to lean on the iac being dirty or failing/faulty. You could take a voltmeter to check the tps sweep.
 
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Originally Posted By: david_ES2
Sounds like a misfire, probably have a bad plug
If they still put distributors on these things in 02 I'd look at that too.
 
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Originally Posted By: Nick1994
Is there an adjustable screw on the throttle body for the idle to raise it up?
Tweaking the hard stop screw is not the answer and masking the issue. The PCM should govern engine speed not an adjustment screw. I would look for an IAC assembly hanging up or a vacuum leak.
 
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Get a proper scan tool on the job and someone who know how to interpret the readings to diagnose it. At this point your chasing your tail.
 
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Idle below 500 is low for a 4 cyl. I think they usually sit around 750 in that car. IAC cleaning might help but I'm not convinced. De-carboning might help, if it needs it. I'd be curious what the compression is across all 4 cylinders. m
 
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Originally Posted By: Lubener
Originally Posted By: Nick1994
Is there an adjustable screw on the throttle body for the idle to raise it up?
Tweaking the hard stop screw is not the answer and masking the issue. The PCM should govern engine speed not an adjustment screw. I would look for an IAC assembly hanging up or a vacuum leak.
Idle air screw-- not the hard stop screw, which should never be adjusted. The idle air screw, if it has one, probably doesn't need adjusting here either. Check the TPS with a scan tool or voltmeter first. Do it when the problem is occurring.
 
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i'm pretty sure its a bad idea to mess with the screw on the iac. its calibrated from the factory and adjusting will make things worse. and do not try to adjust the throttle body. i think etcg was refering to the coolant temp sensor, if it reads off it can cause a rich or lean condition. does it have a check engine light?
 
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Clean the iac.Take off the throttle body. It might be underneath. Pull the mass airflow sensor and clean that. You could also try seafood to clean out the carbon.
 

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Thanks for the replies, guys. I bled the cooling system but that didn't help. There is indeed an adjustment screw on the TB but like others said, it's set from the factory and shouldn't be tampered with. Older Hondas had an adjustable fast idle thermal valve but mine doesn't. Read around on Honda forums and people with low & stumbling idles said cleaning the IACV fixed their issues. I wish the car would just throw a P0505 CEL so I'd know the IACV is the culprit. That bugger is a real [censored] to get to as seen in this pic from a forum write up:
 
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Just bite the bullet. Yank that iac off and clean it up. On those older fords I would clean it every time me I replaced the air filter.
 
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good info from eric the car guy on honda idle problems-> etcg youtube not sure if your motor still has the high idle valve or not. be very careful if you do clean the iac, its easy to ruin them when spraying cleaners in there. but either way be prepared to buy a new one. rock auto usually has the best deal on parts like that.
 
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