Throttle occasionally stops responding

Hi Matt,

This is just a guess but I think your losing the throttle position sensor signal which tells the ECU that your adding in throttle. This is part of the load parameters it needs to calculate how much fuel to add based on load.

Now the reason you can only rev to 1500rpm's is because the ECU doesn't know what the position of the throttle is which is why it's limited to 1500rpm which is the high idle cut off point where it stops adding in fuel. This is part of the programing in the ECU to keep the engine from over revving in case of a vacuum leak in the intake manifold (like as if air would enter in from a bad vacuum hose that's cracked and now air is allowed to enter the engine which is essentially bypassing the throttle plate... the engine reads a slightly lean condition from the O2 sensor and tries to correct it with a slight bit of addition fuel to keep the air mix ratio... but then as a safety measure is only designed to work up to 1500rpm's before that safety system cuts out so you don't uncontrollably over rev the motor).

So basically the engines ECU isn't seeing all the information it needs to calculate the additional fuel... and when it loses that signal from the throttle position sensor (TPS) it thinks you have the throttle closed because it is receiving less then 0.50 volts which would be the signal from the TPS which ranges from 0.40-4.5Volts from full closed to full open positioning. This is why when your driving it feels like the motor isn't running cause it's not providing any fuel to the motor over 1500 rpms... but of course below that it idles fine.

There is a way to test this but it kinda sucks since your car only does this intermittently which means you have to test it when it's failing..... There are 3 wires to the TPS sensor. One is a 5 Volt source from the ECU, The next one should be a ground and the last one should be the signal voltage which ranges again from 0.40 volts to 4.5 volts.. If I were you I'd use a volt meter to test the voltage (preferably an old needle sweep type) which when you have the car in the ON position so the ECU feeds the 5 Volts to the TPS then you can measure the voltage from the sensor signal wire and the ground. When opening the throttle smoothly and slowly opening and closing it the voltage needle should read between that range and be perfectly smooth in motion just like you are moving the throttle. If it has a rough time when opening and closing the throttle, then the signal is dropping out and the needle will move very abruptly which means the signal is dropping out. If it is a bad TPS then you have to get another GTI-R TPS as it is the only Nissan that uses that TPS and is not interchangeable with anything else Nissan has ever made.

The bad news is it sounds like it only happens when the car is hot... this happens cause the metal inside the sensor is worn down and the heat from the engine basically expands the metal inside and you then lose the contacts inside which is why your losing the signal... then you let it sit for a few minutes and the engine cools the metal shrinks and all is well again until it heats up again... Not too uncommon for TPS sensors to do. This is very hard to detect as it's only those seconds when it's failing can you test for it. You can add in a little old volt meter directly inside the Cab from the wires that go to the ECU and monitor or have it on the entire time (basically not a volt meter but a throttle voltage meter) so you can see what signal is going to the ECU at all times... then you can have visual proof that it's failing.

Other things can also cause this same sort of problem which would be bad contact points for the wires to the TPS sensor or to the ECU which is basically a bad connection between the sensor and ECU (brain doesn't know what the leg is doing sort of thing).

I've had a bad connection between the TPS and ECU before in my GTI-R which is why I know about the availability of the sensor and how rare it is. Mine was easily fixed though by making sure the connections were good as the signal was just being lost before it made it to the the ECU... sometimes .... which is why it's so hard to find cause it doesn't happen all the time.

Hope this helps you out as you may need to get help from someone with good knowledge of electronics or a very good mechanic (who sometimes don't necessarily know too much about electronics)

I've had my secondary O2 sensor by the Cat. removed for some time now and I don't think that's the issue at all as your sensor would have to work still and if it did the power loss would be from a melted Cat. and would have power issue from anything above idle all the time as the exhaust would be restricted. The connector to the wires on that sensor are under the front seat which you can just unplug for a cleaner look and this guarantees that the cut wires don't touch each other which may give you a short in the circuit which could possible turn on the dash light every once and awhile.

This is my guess as to your problem but it's at least a semi-educated guess as I have had to deal with it before.

Let me know what you think and if you ever solve the problem let all of us know, as that could help out someone else in the future.

Thanks for the lengthy reply. I'll start looking around for a TPS. I'll definitely report back once I have this all figured out. 

have u tried pulling codes, or running datascan on this?  you can log all ur data instead of guessing whats wrong

No I haven't, thanks for the suggestion. Next time it dies on me I'll try pulling a code.

http://www.canadagtir.com/forums/technical/engine-performance/what-ecutalkconsult-datalog-looks  look through this

cables can be found here http://www.ecutalk.com/interface.aspx  and many other places for probably way less.. i have this one and i like it

I was checking out a few other forums and found a few posts that seem to imply that USDM SR20 TPS's are interchangeable with ours provided you switch 2 wires around. Can anyone confirm this? I haven't taken a look at mine yet so I'm not 100% on visualizing it. Anyway I'll probably pick up a g20 TPS tonight or tomorrow and try this out.

unless you've disconnected the battery, the code should still be in the ecu memory

also, just brainstorming, but check the MAFS plug too

The USDM TPS sensors won't work as they are mounted so that the throttle rotates the opposite direction as the one on the GTI-R. Plus switching the two wires from positive to negative won't work as it's still rotating the one way as the spring is set to one side. I've tried looking at the TPS sensors from a USDM NX2000 with SR20 (same as the rest of the north american FWD SR20's - G20, Sentra SE-R etc..), The JDM FWD SR20 from Neo VVL set-ups, and the JDM RWD SR20 which all rotate the one direction opposite of ours. The JDM Neo VVL TPS actually has 5 wires as the TPS also has an idle switch built in so it knows when the throttle is closed as opposed to just reading the voltage signal.

As for the part number it does not supersede to any known Nissan vehicle.

If you do come across another TPS sensor that will work you'll probable have to get the connector for that specific sensor and splice in the wiring as I doubt it will match your current wiring harness connector.

As for codes, I tried reading for failures and there were no codes that I could find after each time I had that problem. I guess if it happens close enough and often enough together you may trip a code but when it starts to work again and for some time it may not trip any hard codes (just soft ones which need to be tripped repeatedly before becoming a hard code) This may not happen as the problem is intermittent which of course is the hardest to identify.

Yes, using an OBD reader which can give you live data would help confirm whether the signal is getting to the ECU or not but of course you'll have to be watching the screen during the failure to see the results. Also using a digital readout with a numerical display usually isn't very helpful in watching for dead spots or voltage drop out reading unless you are data logging and of course you need to then read or plot them to see what is happening rather then just watching for the needle motion opposed to the movement your making with the throttle (live at that time) If your digital readout does have a graphing display then you could see the wave form moving up and down for a smooth voltage sweep of the TPS signal. Snap-on Vantage tool has that option but then again unless you have it readily available it could be difficult to have hooked up when failure occurs.

Data logging of course would confirm everything after checking the data vs the failure time. but then again logging all your data for the next while could be interesting since your last failure.

A simple thing to try as well like I mentioned earlier is to check the connectors for a solid contact and to clean all pins for a good connection. Make sure the TPS connector is on tight and the clip is clipped on properly. Check for any corrosion on the pins when you have it apart and make sure the bolt holding the connector in on the ECU is nice and snug. Also check to see under your hood if any rodents have gotten under there and look for chew marks on the wiring looms as the little buggers can cause havoc on harnesses.

Hope your research goes well and I look forward to you finding the problem and curing it.

I think i have a similar problem. Does your car still build boost, it just doesnt go anywhere?

disconnect your knock sensor,drive the car then check the code on the computer

I'm not sure. It only goes to 1500rpm so there isn't really anything to build boost with anyway. It can still drive but obviously very slowly.

I've checked codes and it gives me 55 so no help there. I'll try to pull the codes again when the problem actually happens.

khrys, thanks for the insights. Ended up working on my brakes today (this car is always one step ahead of me lol) so didn't do any fooling around with the TPS. I'll try to find a legitimate one instead. BTW, I unplugged the secondary O2 sensor properly under the seat. I know it shouldn't have anything to do with this issue I'm having but its been bothering me that the cat light always seems to turn on just before and exclusively when the throttle is about to give out. Just eliminating a variable.

the cat sensor just tells u shit's overheated.
it's not wired into ecu nehwere, its a direct line to the dash

Just an update, since I unplugged the secondary O2 sensor under the seat over a month ago I haven't had any throttle-dying incidents with my car and I have been driving it everyday. I ordered a spare TPS from England and its come in but I haven't installed it since there doesn't seem to be any need.

The GTIRs run OBD1 so there is only 1 o2 sensor on our cars. It's a coincidence that unplugging the EGT sensor from the catalytic converter has cleared your issue. The CPS could also throw your car in limp mode. Let us know what your findings are when the problem happens again.