Very irregular idle 850 - 2800 rpm

[mdb]

Not sure what to make of this. The water temp sensor in my car has alwasy been a little flakey, which seems to get it confused on occasion so it would kick into warm-up idle randomly, but very rarely. The past two days the behavior has been this. Start it cold, the rpms are 1400 or so. It warms up and drops to 850, very stable (run the AC, headlights, whatever). As I drive the car a bit, the rpm will drop when I clutch in to around 1000, then shoot back up even higher. After 15 min or so, its hitting nearly 3000 rpm and holding it. Go a bit longer and it starts bouncing back and forth between its current high and 1200 rpm very rapidly. Shut the car off for 5 min and the process starts all over again (minus the initial warm-up rpm).

I've adjusted the idle, reset the ECU several times, and checked all the connections. Thoughts? Can I safely run the car with the EACV unplugged until I can get this looked at? The car is hard to drive around town in this condition.

Thanks,

Martin

 

[NA1 #2853]

Another thing you might want to look into is the Fast Idle Valve.

It is very common the on Hondas for this to go bad. Most places will have you replace the unit, but every one i have seen go bad i have been able to repair.

What happens is the plastic stopper inside the unit has backed its way out of its threaded reciever. You must pull the Fast Idle Valve off the engine, and unscrew the cover place, and thread the stopper back into the reciever.

I'm in Tacoma, maybe after i get back from SEMA we can meet up..... I'm leaving early tomorrow and wont be back until late thursday.

-Ray

 

[Larry Bastanza]

Ray,

Sounds like a high probability, your suggestion of the FIV. Good to know and thanks for the tip on fixing it.

mdb,

You ask: "Can I safely run the car with the EACV unplugged until I can get this looked at?"

Are you implying that the problem goes away with the EVAC unplugged? Certainly an important clue.

Thanks,
LarryB

 

[mdb]

Thanks for the info. Played around with it some more and here's what I've got. If I cork the air line for the fast idle valve, it doesn't seem to make a difference, so I think its OK. If I unplug the EACV, it idles at 650 and the problem goes away, but it will also die if I turn on the AC or the radiator fans come on. That also gets a check engine light. If I unplug just the water temp sensor, I get a check engine light, and even with the engine cold, it immediately shoots to 2100 rpm and gets worse from there. I was hoping it would default to a "warm" value with the sensor unplugged but I guess not.

 

[Briank]

I think you answered your own question, if the temp. sensor is lying to the ECU the idle speed will be all over the place. Take care of the sensor problem and your idle control problems will be gone. Your car has 3 coolant temp. sensors one for the gauge, one for the fan and one for the ecu. The connector for the ECU temp sensor is a 2 pin grey one located is infront of the EGR valve and very close to the green connector on the spool valve.

Something else that comes to mind is you may have a thermostat that is sticking open sometimes because of what you said about the gauge acting screwy some times. If your stat sticks open the coolant temp will fall and the ECU will raise the idle speed.

 

[Larry Bastanza]

mmm...

Sounds to me like the EVAC is the issue. If you disconnect it and you idle at 650rpm with no issues accept the stall with the A/C on it sure sounds like the temp sensors are working OK to me.

JMO,
LarryB

 

[Briank]

http://www.nsxprime.com/FAQ/Reference/1991_svcman/1991servman.pdf

Starting on Page 242 of the PDF file is the idle control system section.

From what I read unless you are getting a check engine light code 14 your EACV is ok. On page 245 of the pdf file it lists what to check.

After re-reading you original post and the part about the idle speed getting erratic after pushing in the clutch I would look into the clutch switch /signal. The switch just may need to be adjusted. Have you had any recent clutch master cylinder work done?

 

[mdb]

Thanks for all the info. I was originally thinking it wasn't the temp issue given how high the idle was going. I thought 1400 was about tops for warmup high-idle. The car warms up quick enough even in the sub-freezing weather we're having right now, so I think that means the thermostat is allright. Clutch in or out doesn't seem to make a difference either

Whatever it is, it starts doing it immediately now. I've also started getting a somewhat large cloud of smoke every seventh or eighth time I start it (smells like Castrol). Not sure why that would start now I was going to drop it off at Torque Freaks to get my AEM tuned and a leak fixed, so I think I'll park her for now then just run it down to Portland this weekend and have them check everything out. I'll wrench on my motorcycles and Fiats, but the NSX is a bit complicated for me

 

[Larry Bastanza]

mdb,

Opps, hold the phone!!!!

"I was going to drop it off at Torque Freaks to get my AEM tuned "

I cannot believe I never asked the most basic question. I thought the car was stock

I will retract all diagnosis at this point. It may just need to be tuned.

Good Luck,
LarryB

 

[mdb]

No, she's stock. AEM is still sitting in a box at the moment, so carry on with the useful tips!

 

[mdb]

Might have it! Did some more poking around, and found putting pressure on the throttle position sensor (angle sensor?) made the erratic behavior almost stop. Unplugging it gets a solid 2000 rpm idle, and with the connectors cleaned up a bit it idles solid around 850. It will jump up as soon as I touch the gas to around 2k or so, then slowly drop back down to 850. I believe it shares a ground and pin at the ecu with the water temp sensor as well. Hmmm.... Got some more manual reading to do