Trying to resolve high idle *with pics*

[vandale]

Hello to all,

I have owned my 88,000km 1992 JDM NSX for appox 8 weeks and have done the following bits and pieces:

Engine Oil and filter
Spark Plugs
Coil pack replacement
19 inch wheels
HID headlight kit
Lowered 38mm
New bump stops
After Market rear upper arms
Inner/outer front tie rods
front shocks
Type R gear shifter
General tidy up
Fuel Filter

I am at a stage where I am happy with it mechanically and cosmetically but I have one small issue, the engine idles too high, it has done this from when I received it from Japan.

This is what I have done to try and rectify the issue:
Cleaned and tested the EACV (within spec).
Cleaned and tested the Fast Idle Valve (within spec).
Checked ECU for codes (none).
Replaced air filter, plugs and coils (not for this issue but did not make a difference).
Checked the clutch, aircon and alternator idle sensors (within spec)
Checked the ECU and another ECU (within spec).
Vacume tested all vacume lines, also sprayed ether in engine bay and did not see a rpm rise.
Followed the Honda NSX service guide all the way through the Emissions and Engine Electrical sections without success.

The engine idles around 1500 rpm when cold and within 5 mins (when radiator fan comes on) it drops to 1100rpm.

I have read alot of posts saying clean the throttle body, I sprayed carb cleaner into the throttle body while lifting the revs, this did not make a difference so I removed the intake manifold and body, pics are attached.

My questions are:
Is it supposed to have oil pooling in the bottom of the throttle body as pictured?
Can I removed the butterflies or are they there for a reason other than fuel economy?
What else could be causing the high idle that I have not already tested, I am in New Zealand and cannot afford to be replacing parts to rule out a fault (NSX prices here are grossly inflated ($250 front bumper toe cover, $900 ECAV, $300 Coil pack etc.....)

Hopefully I can get to the bottom of this, I will clean the throttle body and put back together and see where I am then, feedback is appreciated.

Regards

Gene
NZ

Pics:

 

[Larry Bastanza]

You do not mention that you actually adjusted your idle by using the idle adjustment screw. Have you tried to slow the idle by adjusting this on the throttle body?

Normally this is not touched and the screw is actually painted shut. I do not know if someone prior to you may have tampered with it.

HTH,
LarryB

 

[davidf]

I wonder if it's possible over time/miles for carbon/gunk to build up inside the idle control motor airway passage, thus causing the thing to stick. I've replace a many IAC's on Crown Vics in the past from irratic idle. Completely solved the idle problem but wondered if a thorough cleaning would remedy the issue as well.

 

[vandale]

You do not mention that you actually adjusted your idle by using the idle adjustment screw. Have you tried to slow the idle by adjusting this on the throttle body?

Normally this is not touched and the screw is actually painted shut. I do not know if someone prior to you may have tampered with it.

HTH,
LarryB

Yes I have chipped away the wax and adjusted this and it drops the revs about 100 rpm more. I was reluctant to say I had as previous posts state 'NEVER' adjust this screw as it is set at factory etc....

Thanks

 

[Larry Bastanza]

The next thing to do is check that the throttle plate is actually fully closed when you are not engaging the throttle pedal. Maybe you have a throttle cable that is set too tight.

I think you need to check this two ways. If the throttle body is off the car, use a light to make sure it is shut on the inner bore.

Once assembled on the engine you can disconnect the throttle cable and see if it results in the idle going down. If so, you need to adjust the throttle cable.

HTH,
LarryB

 

[vandale]

The next thing to do is check that the throttle plate is actually fully closed when you are not engaging the throttle pedal. Maybe you have a throttle cable that is set too tight.

I think you need to check this two ways. If the throttle body is off the car, use a light to make sure it is shut on the inner bore.

Once assembled on the engine you can disconnect the throttle cable and see if it results in the idle going down. If so, you need to adjust the throttle cable.

HTH,
LarryB

I have cleaned and reassembled the manifold, replaced some old water hoses.

The engine idles still high at 1200rpm, no change after cleaning all that oil and junk form the throttle body.

I have removed the acc cable and no its not to tight, I see there is a throttle stop adjustment but that says not to adjust as set from factory.

I am starting to lose hope as I have done everything the manual says plus more. Could it be an oxygen sensor, or crank/cam sensor causing this without sending codes to the ecu?

Thanks

 

[EdinKali]

Are you sure it is really idling at 1200 rpm? Have you hooked up an external tachometer to make sure your dash tach is correct? Many OEM speedo's and tach's are not very accurate.

 

[vandale]

Are you sure it is really idling at 1200 rpm? Have you hooked up an external tachometer to make sure your dash tach is correct? Many OEM speedo's and tach's are not very accurate.

Yes I am using an external tach.

A few minutes ago I adjusted the factory set throttle stop, when I did this the revs dropped to 900 odd but would fluctuate from 900 to 1500 every few seconds, if I then adjusted the idle bypass screw while the throttle screw was backed off it would settle down and idle around 1000.

But........

The throttle would stick in the housing as it has gone to far past home position, I have put it back and am currently idling around 1100.

My throttle housing and butterfly are in pristine clean condition so it is not sticking due to being dirty.

There is an adjustment screw on the EACV but it is factory set and glued in, also the hex head shape is strange looking, I have the screw driver that fits this so that will be my next step, its a pain though because the EACV has to be removed to adjust this.

I have 2 questions:
What does the EACV adjustment do?
All the vacume pipes running off the manifold go to a black box, could it be a solenoid in here that is causing the issue? How can I check?

Regards

 

[EdinKali]

What happens if you turn the AC on? Does the idle go down? If so the solenoid that controls that may be stuck on. The idle should stay roughly the same when you turn on the AC despite the load. If it is stuck on all the time the idle will be too high when the AC is off.

 

[vandale]

What happens if you turn the AC on? Does the idle go down? If so the solenoid that controls that may be stuck on. The idle should stay roughly the same when you turn on the AC despite the load. If it is stuck on all the time the idle will be too high when the AC is off.

According to the Honda manual, the EACV does that. I just checked now and when you press AC it spikes for a milisecond and then stays the same so it looks like it is working.

 

[96cxt]

if you have checked the throttle cable and the TB itself, then either you have a vacume leak (check you gaskets on the manifold), or your injectors needs to be cleaned and balanced.

 

[FastraxTurbo]

Check your pcv valve and hose. Pinch the hose or plug the end of the pcv valve to see if the idle drops. A slight drop in idle is normal, as the valve permits a controlled amount of vacuum to pass.

 

[vandale]

Check your pcv valve and hose. Pinch the hose or plug the end of the pcv valve to see if the idle drops. A slight drop in idle is normal, as the valve permits a controlled amount of vacuum to pass.

Thanks but I have tried that, I also sprayed ether around all possible places near the inlet that could be leaking vacume, non found.

I followed the service guide to set idle which says to disconnect the EACV, turn the idle screw out 1 turn and set it to 550rpm. Then reset ecu, plug the EACV in and idle should read 850ish. I have already tried that so went about it in a different fashion. If you unplug the EACV the engine check light comes on so I unbolted the EACV from the manifold but left it plugged in. I placed a sheet of rubber over the inlet holes where the EACV was removed (to stop vacume leak) then started car. It idles at 550 as stated in the manual, the second I put the EACV on it idles to high again no matter what I adjust.

Process of elimination says the EACV is faulty so I will replace that soon, they cost $950NZD from Honda Japan.

The EACV has a tamperproof screw in the side that applies pressure to a spring inturn providing pressure on the EACV valve, if I wind this out I can get it to idle within spec but when the engine is shut down and restarted it the fluctuates idle between 800 and 1500 and will not settle. Unsure why.

So it looks like the EACV is at fault unless anyone has experienced this and can offer advise on fixing the EACV valve? If not then time to start saving.

Cheers

 

[drew]

Did you test the water temperature sender?

If it is sending out a signal that it thinks the coolant is cold, the computer will bump up the idle speed.

**

I don't think messing with he idle adjustment has solved any problems for anybody. If it didn't need replacing before, it likely does now.

**

The butterfly valves are for on the fly intake tuning and increasing volumetric efficiency.

 

[vandale]

Did you test the water temperature sender?

If it is sending out a signal that it thinks the coolant is cold, the computer will bump up the idle speed.

**

I don't think messing with he idle adjustment has solved any problems for anybody. If it didn't need replacing before, it likely does now.

**

The butterfly valves are for on the fly intake tuning and increasing volumetric efficiency.

This one?

Thanks

 

[Ciphernet360]

Vandale - I hope you have not given up, but this is the exact same issue that I am having. Question on your second pic, these internal valvles, do you think it could be the actuator that runs these causing an issue.

Since you and I are having the same problems, let me run down what I have done and repalced. Note, all this has been done and I am having the exact same problem with my car wanting to idle at 1500 + rpm, not wanting to settled down and slowly going back up again:

- Just checked Fuel pressure today 4-18-2010: My PSI is at 40 Psi (within spec)
- Fully cleaned throttle body and reset idle at 550 rpm according to manual (within spec with EACV off) (out of spec when EACV plugged back in)
- Replaced both the fast idle valve and EACV valve with factory new parts (did not solve issue)
- Replaced injectors (did not solve issue)
- Replaced with new O2 sensors (did not solve issue)
- Replaced with new spark plugs (did not solve issue)
- Replaced with new main relay (did not solve issue)
- Tested output of altinator (within spec)
- Replace battery with new Optima Battery (did not solve issue)
- Cleaned air filter (did not solve issue)
- No Check Engin Light
- Check hoses, sprayed under engine compartment with starter fluid to check for leaks (noticed no change in RPM)

I now have a Throttle Position sensor on order and will be replacing that shortly

I'm in the same boat man, can' seem to find the problem, reading the manual and diagnosing like you -- it's a phantom problem that nobody seems to have the answer too.

I'm now trying to hunt down a coolant sensor to see if that needs to be replaced. crazy man, crazy and frustrating. I don't even know if a shop could fix this.

Ciphernet 360

hit me up at [email protected] and let's exchange ideas since we are troubleshooting the same issue.

 

[R13]

I had this issue and resolved it between replacing the water temp sensor & EACV. Full disclosure: I did also clean the TB and replace the filter screen on the fast idle valve at the same time.

I'll second the sensor replacement suggestion as it appears several people have covered the other bases, but not done this.

 

[Thunder]

I found this on Internet, hope for how that will help you!:smile:
this topic does not speak about NSX but about disorder of idle for any Honda engine, for the NSX, two points important has to control, to control if the coolant circuit is well purged (not of the bubble air in the circuit), to control if the calorstat (thermostat) coolant circuit does not remain in position " open" , to dismount and control O ring, old O ring blocks the closing of the calorstat! distorted data ECU what gives an idle " yoyo"

http://ef-honda.com/ben/Badidle.php