Engine revs up and down and then stalls!

[snake11eyes]

I have a '94 NSX with 100K miles and recently started experiencing this strage problem. When I start my engine, the tach shows the engine rev-ing sporactically up and down (approximately between 800-1200 RPMs, which seems like a large range). About 3 times over the last week, the car stalled during this sporactic rev-ing within 2-3 mins of me starting the car.

I have only experienced this so far in the morning when the engine is completely cool so I'm not sure if this is coincidental or has something to do with the fact that the engine is completely cool in the morning. Otherwise, i have not experience this problem when leaving from work in the afternoon...presumably maybe because the engine is somewhat warm from being out in the sun? Also, I have noticed that this seems to be made worse when I turn the A/C on...this makes the sporactic rev-ing more pronounced (rev's between an even wider range...maybe 800-1500 RPMs). Again, I'm not sure if this is coincidental either but I'm just trying to give all the facts.

I just had all of my major service (timing belt, water pump, belts, hoses, fluids, spark plugs, valve adjs, etc.) done a couple of months ago (and by Ramon and Niguel Motors no less) so I'm really perplexed as to why this is happening.

At this point, it is only an irritation because I have been able to just restart the car (maybe once or 2 or 3 more times before it will not sporadically rev and stall) and I'm on my way driving. However, I don't want it to get to the point where I won't be able to start my car at all or worst yet where it will be a safety hazard and stall when I'm driving in traffic.

I'm really ANXIOUS about this as its my daily driver...someone PLEASE HELP!!!

As always, thanks in advance.

 

[shawn110975]

Main Fuel relay. or ignition switch. if its stalls then starts right back up.

both of these parts are fairly cheap. 160 for both from the dealership.

had a similar problem, but when it would start it would idle then die, if I started it up
and floored the gas it would red line for a second or so then die again, my alarm shorted it out, ( Alpine )

 

[Jin1976]

I have same problem. My solution is everytime the engine do that I just floor the gas a lit bit and the rev stabilize. Maybe clogged throttle body. I'll try to clean it later.

 

[AdvansCPAP]

Fluctuating RPM usually is due to a intake hose vacuum or exhaust leak near the 02 sensor. It's an air/fuel mixture problem and will almost always be worse with the AC on.

If you never had this problem before the major service, my bet is something wasn't put back on correctly. Also, since it is an intermittent issue and happens when the car is cold, I would say it's coming from a part that is made of metal and is either cracked/loose or shorting out.

Two majors areas you would want to focus on is the intake and all the vacuum lines. Another area would be the area next the 02 sensors, wires and its connections.

While the engine is on, wiggle every single rubber hose and electrical wire/connector coming off the motor to see if the movement of the part will re create the issue. If nothing, then go under the car and wiggle the 02 sensor wiring and see if its properly tied away from the header. If you have after market headers, air can be entering from a crack in a weld or joint thus throwing your 02 sensor off.

One other issue is carbon build up in your throttle body and lines. It can easily be cleaned using throttle body cleaner.

 

[snake11eyes]

Thanks for the tips guys. I'll try some of these suggested trouble-shooting tasks when I can free up some time. In the meantime, based on how I describe the problem, is it a safety issue? I.e., Do I need to worry the car stalling while driving in traffic or can I assume that once it's started up and in motion, I should be okay?

PS I did a search on Prime and couldn't find much information on cleaning the throttle body. Most posts just say "clean the throttle body." But for a novice like me, I don't know what that means. Can anyone point me to a go DYI or give me detailed, step-by-step instructions?

Thanks!

 

[nsxtasy]

This was happening to my car at NSXPO 2006, where fortunately Nabil Armily of First Class Automotive - the best NSX mechanic in Florida - was around to check it out. First he tried cleaning out the throttle body, which did not fix the problem. Then he replaced the idle control valve. THAT fixed the problem.

 

[ryan1926]

This was happening to my car at NSXPO 2006, where fortunately Nabil Armily of First Class Automotive - the best NSX mechanic in Florida - was around to check it out. First he tried cleaning out the throttle body, which did not fix the problem. Then he replaced the idle control valve. THAT fixed the problem.

Would you happen to know the part # for the idle control valve for a 1995 NSX?

 

[dlynes]

my car does the same thing...

I have had two majors done in the past 6 yrs

 

[Speedmaster]

Glad I found this thread...just got my NA1 back from a TB/WP, Valve adjustment...

Fluctuating RPM usually is due to a intake hose vacuum or exhaust leak near the 02 sensor. It's an air/fuel mixture problem and will almost always be worse with the AC on.

If you never had this problem before the major service, my bet is something wasn't put back on correctly. Also, since it is an intermittent issue and happens when the car is cold, I would say it's coming from a part that is made of metal and is either cracked/loose or shorting out.

Two majors areas you would want to focus on is the intake and all the vacuum lines. Another area would be the area next the 02 sensors, wires and its connections.

While the engine is on, wiggle every single rubber hose and electrical wire/connector coming off the motor to see if the movement of the part will re create the issue. If nothing, then go under the car and wiggle the 02 sensor wiring and see if its properly tied away from the header. If you have after market headers, air can be entering from a crack in a weld or joint thus throwing your 02 sensor off.

One other issue is carbon build up in your throttle body and lines. It can easily be cleaned using throttle body cleaner.

Service and my idle is now jumping all over the place. Never did this before. I am talking 750-1100.

I am happy to go look under the hatch, but this is nuts.

 

[AdvansCPAP]

Air bubbles that have not been bleed out completely from the cooling system after service can get trapped in the Idle valves in the throttle body. This will cause your idle to bounce as well.

 

[shawn110975]

+1 on that

 

[Speedmaster]

Air bubbles that have not been bleed out completely from the cooling system after service can get trapped in the Idle valves in the throttle body. This will cause your idle to bounce as well.

Now THAT is interesting...since the hop is an our's driv away, is there a low-tech way to bleed them out? Or, is this a self-correcting situation?

- - - Updated - - -

Air bubbles that have not been bleed out completely from the cooling system after service can get trapped in the Idle valves in the throttle body. This will cause your idle to bounce as well.

BTW-thank you for posting the response!

 

[shawn110975]

The trick to bleed the system is raise the rear of the car as far as you can I mean as far as your stands will allow, you wanna get a good angle maybe on a downward driveway and then raise the rear up,

open the front upper rad bleed screw

then the bleed screw next to the coolant reserve and the one under the throttlebody.

start filling it when you see perfect flow in the front screw it tight,

keep filling till the one next to the reserve on the firewall is bubbling up wait till its a perfect stream tighten down ( 12mm )

next is the one under the throttle body it will bubble then stream tighten

total fill is 3 jugs if empty if your gonna bleed the system with it almost full you may need a half jug

then lower car drive around take some corners zig/zag anything you want, make people think your Drunk LOL then go back home raise car again but this time only open then a little you will hear a hiss and then a stream do this to all 3 and your done.

 

[Speedmaster]

The trick to bleed the system is raise the rear of the car as far as you can I mean as far as your stands will allow, you wanna get a good angle maybe on a downward driveway and then raise the rear up,

open the front upper rad bleed screw

then the bleed screw next to the coolant reserve and the one under the throttlebody.

start filling it when you see perfect flow in the front screw it tight,

keep filling till the one next to the reserve on the firewall is bubbling up wait till its a perfect stream tighten down ( 12mm )

next is the one under the throttle body it will bubble then stream tighten

total fill is 3 jugs if empty if your gonna bleed the system with it almost full you may need a half jug

then lower car drive around take some corners zig/zag anything you want, make people think your Drunk LOL then go back home raise car again but this time only open then a little you will hear a hiss and then a stream do this to all 3 and your done.

Thanks for this Shawn.

I am inclined to call the service department and have them come pick this up and fix it. Burns me up that I just dropped big coin and they didn't get this part right.

 

[shawn110975]

have them pick it up on a flatbed don't want some young kids getting a dream drive alone all the way back to the dealership Nope.. and if there are bubbles causing it to rev like that what if it stalls on the way there at the right moment as he is turning and get T boned, or worse.

 

[Briank]

Most common cause of a high hunting idle is a vacuum leak.

 

[shawn110975]

or base idle is outta whack

 

[Honcho]

Most common cause of a high hunting idle is a vacuum leak.

+1

In most cases it is a bad Fast Idle Thermo Valve (FITV), which is used only on 91-94 NSX models. This is a wax-filled plunger valve that opens and closes depending on coolant temp. In most cases, the plunger becomes loose and causes an intermittent vacuum leak. In other cases it becomes dirty and can't make a good seal. Most Hondas of this vintage suffer from this problem. Most people just replace it when it goes bad- about a hundred bucks from Rock Auto.

However, there are a lot of vacuum connections on the C30A and one of them was disturbed from the TB job, that could explain it too, but usually in that case, you'd have a high, stable idle, since the vacuum line would be open all the time.

Therefore, my bet is on the FITV.

Edit: Below is a link that shows the valve.

http://www.nsxprime.com/forum/showthread.php/178307-Intake-Manifold-Overhaul?p=1751583&viewfull=1#post1751583

 

[nick.ma3kie]

I have a similar issue

My 1996 Honda Civic over revs the stalls but does not turn back on. It was stolen and taken for a joyride not too long ago and came back in this condition, what could it be?