Strange throttle not responding issue

[nsxbuilder]

Hey crew,

Situation: 1991 NSX starts and drives happily. Car comes up to temp. At a stop light where the car sits at idle 1-2 minutes, press the accelerator to go and nothing happens. Franticly feather on/off the throttle to see what the heck and it finally decides to work like a gas pedal again. This happened once last year, and I blew it off as voodoo/phase of the moon, but now this season its happened 3 times. The last time it wouldn't come back so I turned off the car, restarted it and it still didn't work, but after 3-4 presses of the pedal it came back.

Also, after turning off the car at my destination, I could smell a hint of coolant when I got out. I recently replaced all the hoses, and am running the Prospeed Big Throttle Body and RDX injectors (for a couple years now), if that matters.

What gives? TPS sensor going out or adjement issue? I'm running fresh premium gas with no ethanol, so I don't think its that, and throttle comes back and always works when cold, so it shouldn't be the throttle cable.

Needless to say having the traffic behind you think you are going to move and you don't is not a good condition.

Anyone seen/heard of this before?

 

[B2FiNiTY]

Have you checked your throttle cable for slack or snagging? Maybe even fraying.

 

[Old Guy]

Ditto on making sure that the throttle cable and operation of the throttle plate is OK.

The TPS is not super critical to engine operation. Most engines like the NSX which are gamma x N (as opposed to alpha x N) will operate OK (with deteriorated response to acceleration and some trailing throttle overrun) with the TPS disconnected. The primary signal for increasing engine output comes from the MAP sensor. If the throttle plate operation is smooth, have a look at the vacuum line to the MAP sensor. Make sure that it is not obstructed, If the MAP sensor does not detect a changing manifold pressure which is a sign of the throttle opening, the engine is going to sit their doing nothing. The MAP sensor could also have a bad electrical connection so the ECU is not getting the signal. On OBDII cars I think this would generate an error code. I am not sure about pre OBDII cars.

 

[nsxbuilder]

Thanks for that - I'll have a look!

 

[nsxbuilder]

It did the same thing to me again today. After being very mindful of sitting at long rush-hour stoplights and occasionally revving the engine at all of them with no issue, 45 minutes into my return to home I stopped at a light and didn't rev during the stop. The light turns, I press the throttle and nothing - no change in my tach revs at all. I feathered it about 10 times before it finally decided to work again, and then the rest of the way home was happy as ever.

Guess I'm pulling the throttle body off and inspecting everything...

 

[GraemeD]

Any fault lights illuminated?
Just a wild ass guess, the traction control system failing? (that is the only thing I can think of that would prevent the throttle plate moving with the throttle cable.)

my thinking is if the throttle plate opens, more air is going in no matter what, and if any of the sensors (map) are bad, it will not correct (increase) the fuel flow, end result is too lean and the engine dies.

 

[nsxbuilder]

No fault light, no TCS light, engine idles away happily until I thump the pedal a few times and then it works fine for hours...got a mystery on my hands here!

 

[nsxbuilder]

UPDATE: After still not finding the source of this occasional lack of throttle from idle, I decided to disconnect the TCS control on the side of the throttle body. Of course my TCS light comes on right away, but I haven't had the issue in the last couple sessions of driving. I'm not saying conclusively, but it makes sense that the only thing that can disengage the throttle control from the pedal is the TCS. I'll leave it off through NSXPO and see if its happy - and if so send my throttle body off for a do-over. Those aren't available as a separate part, and the throttle body is now discontinued from Honda. Nice.

 

[Larry Bastanza]

I am thinking this may be a typical electrical fialure of the capacitors on every module in the car. Make sure you discuss with BrianK at NSXPO...... Assuming it keeps working fine with the TCS off.

 

[Tommycortez]

I am having the exact same problem on my 91 Nsx as described, Did you ever find the problem?

 

[nsxbuilder]

The issue did happen again with the TCS disconnected at the throttle body. After reconnecting it I finally got a TCS error code that pointed to the throttle body itself. I just got a big throttle body from SOS and a new fuel pump/filters while I was at it, and after installing both, so far so good - problem seems to be gone.

Interesting side bar, I was also having a throttle hesitation when taking corners quickly...it would literally feel like TCS was coming on. I started looking around in the engine bay and found the big ground strap that goes from the frame to the tranny was frayed. I went up to NAPA, got all the stuff to make new ones and put a new ground on both sides of the engine and that issue is gone. I guess with out older cars we need to start looking at a lot more than just the standard maintenance items.

 

[Tommycortez]

Thanks for the quick reply, I will be installing my walbro fuel pump next from SOS. I already put one good ground on the transmission to frame, I will look at the engine ground. Maybe your throttle position sensor was going bad , I’m going step by step so maybe this can help someone else.

 

[Tommycortez]

I have turned the TCS off while I drive and the problem has not came back when I’m at a stop light . I then drove the following day with the tcs engage and it stalled or sputtered at the stop light. I don’t have a tcs light on when this happens. It happens from a stop and slowly accelerating. I have to let off the throttle and re engage the throttle to get going. It doesn’t happen all the time , the problem is intermittent, but I now believe it has something to do with the tcs. I will keep driving with the tcs off to see if the problem returns.