UPDATE::::

ALL FIXED THANKS to mk378. I tested the Engine Coolant Temperature Sensor with a multimeter and it was way off. Replaced the sensor and RPM went from 1500 to now normal 700!!!!

After researching, turns out the bad ect sensor was actually aftermarket and was not genuine Honda part!! No wonder it was under 10 bucks! Fake Honda sticker on the package too. Be careful! Real ones cost 50







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My vehicle is having a high idle issue.
Stays at about 1500rpm steady when the engine warms up.


This is what has been done to diagnose with no luck:

Idle Air Control Valve:
Tried an aftermarket one, tried a used oem one, and even bought a brand new oem IACV $220

Vacuum Leaks:
Sprayed all the hoses with brake cleaner, rpms didn't increase or decrease. Tried this method over 3 times already. Also tried the pinching method.

Coolant:
Properly bled the coolant, heat is blowing hot from the vents.
New coolant sensor

Throttle Body:
TPS sensor was tested .45v when closed 4.95v when fully open.
Tried a used throttle body from a 94 civic vx and put new gasket
Changed map sensors
blocked the hole inside, and rpms dropped to below 500rpm. if blocked longer than 3 seconds car dies.
adjusted the idle screw properly

EGR Valve:
Cleaned the valve, also tried a used EGR valve from a 94 civic vx.

Distributor:
Timing adjusted, new spark plugs

Other:
New PCV Valve
New Oxygen Sensor, also tried disconnecting it to see if it could be the problem.
Tried a different ECU from a 92 civic vx
Block test, there is no head gasket leak
Fuel pressure test, pressure was in spec I believe it was 45psi non running and 32psi when running
New Air filter
tried stock fuel injectors and same problem



I am running out of ideas on how to fix this high idle
Can carbon buildup somewhere cause high idle?
EGR port in the intake is partially clogged up with carbon buildup

 

> blocked the hole inside, and rpms dropped to below 500rpm
You're very close to finding the problem there.
It can't run fast (or at all) without air. Something related to that hole is letting too much air into the intake.
I don't know about the VX but the other ones actually have three holes, one at the bottom for the FITV, one in the center for the IACV and one nearer the top for the idle air adjusting screw. On those only the screw one should be drawing air when the engine is warmed up (FITV closed) and the IACV is commanded closed by the ECU or unplugged.

 

oh yes sorry it actually died the longer i hold the hole closed. i did it couple times and i didn't want it to die so it was like holding it closed for few seconds to test if rpms dropped at first. it definitely dies within 4-5 seconds of holding it closed.

 

Sounds like you need to clean the FITV

 

Which hole are you covering with your finger ? The finger sized holes are found at the 8 o'clock and 10 o'clock position as you face the throttle body from the right side of the car.

 

When u say adjust the idle screw properly, walk us through what u did. Also, did you relearn the idle after resetting the ecu?

 

Permission to post

Can someone help me on how to reduce the idle RPM? My car is 97 civic AT and the screw is almost close but still getting >1000 rpm at no load. When you switch the aircon, RPM will go down to 800 for the initial 15 to 30 mins of running. After that the RPM will be at 1000 slightly higher, when aircon stop it goes less 1000rpm. When I park and turn off the aircon, the rpm is at 1200

 

I'm always shocked how many people get this wrong, (either miss a step or assume that a few of them are unimportant)
Then again I was doing it wrong for many years also...

 

I did what was said in the book.

1. get normal operating temp, fan turned on
2. disconnected IACV plug
3. for the vx, i adjusted the screw to as close as I could to 420rpm. thats what the book said without the IACV connected. I don't have a tach reader so I estimated as close as I could to around 400.
4. turn off the car, and re-connected the IACV
5. started it up again and still high idle

this is the first time i did that out of many tries

second time:
i did everything above but i reset the ECU after adjusting idle screw to around 400, after resetting ECU, i restarted the car.
no luck

third time:
I started messing around a lot more with the screw like putting it all way way screwed in to see the lowest idle i could get and it was around 1300rpm.

i have a strong believe that the culprit is not the idle screw



please let me know the right way to do it and how to "re-learn" for the ecu

 

the vx does not have the fast idle valve

there is only one hole and it's the 10' clock position, when covered completely the car will die

 

You did the base idle adjustment correct. Since it is idling around 400 without the iacv plugged in, i’m inclined to say that the prob is within the iacv/ecu/wiring

relearn procedure with engine full operating temp, pull backup fuse for 10+ Seconds, replace. Start car, let idle for one minute with everything off(radio headlights defroster ac, any accessory). Next turn on headlights and rear defroster, let idle one minute then turn off accessories. Third turn blower fan to highest setting with AC ON, let idle one minute. You have now relearned idle. First two should be roughly 750 and third (ac) should be roughly 850. These idles speeds are approximate and can vary by 50rpms.

side note: my fluctuating idle was caused by a failing o2 sensor.

 

If the ECT sensor thinks the engine is cold, the ECU will command the engine to idle fast. Test ECT sensor with an ohmmeter. It can be out of spec but not far enough to cause a code. OBD1 codes generally mean something is really wrong. There are no codes set on your car, right? If there are you need to resolve them.

The regular OBDI ECUs don't have any memory process to "relearn" but again the VX could be different.

 

I've never seen the ect make the engine idle that high, like 1.5k rpm high, but its worth a look.

 

The VX uses a 2 heater wide band O2 sensor and EGR system. The O2 sensor I believe can affect idle unlike other trims as was mentioned by another VX owner. I'm not sure if the EGR system can affect idle but that might be another possible avenue needing investigation.

 

THANK YOU SO MUCH!!@!@!
I bought the ECT sensor last year brand new! today I tested the sensor with the multimeter and behold, it was wayyyy off!!! it was reading .356 with a m symbol and it should have been over 2.000+ with a k symbol.
Luckily I had a spare ECT sensor and tested it, it read 2.340k in room temp. So I installed the new ECT sensor, attached the no-spill funnel to the radiator, filled up coolant, started up the car, bled the coolant properly. My RPM is now about 700!!!!!!!!!!
This also fixed the rough cold start!! it starts smooth now.
THANK YOU!!!!


It was worth the look, my rpm's went from 1500 to now around 700!!! just by changing my ECT sensor that was only just over a year old!!