This is more of an FYI rather than a question. But i thought it might be helpful to some. (I actually dont have a 300ZX, but its still a VG30DE, in F/R layout) The first signs actually seemed more like a sticky throttle cable than a TPS problem. After accelerating with full throttle it to join onto a freeway, sometimes the throttle would stay open after i let off the accelerator. It would always correct itself when i blipped the accelerator pedal though, so no biggie. I tried lubricating the throttle cable, but the problem kept coming back Then the other night i took off quickly from a traffic light, only to have the same thing happen. But this time, blipping the accelerator did nothing. It just kept going! On the freeway its not so scary, but when you have 20 other cars around you doing 50km/h its dangerous as hell. Managed to hold the acceleration with the brakes, but when i tried to turn off the main road, of course the rear wheels lit up - resulting in an unintentional powerslide until i could kill the engine and come to a stop. Checking with ECUTalk on my PDA the problem was obvious. TPS read 2 volts at closed throttle, but moved smoothly from there up when i touched the accelerator. Stomping on the accelerator brought the reading down to 1.9, then 1.8, and so on, until it finally went down to the normal 0.46. But when i tapped the accelerator, it went back up to 1.5 and stayed there. So I have ordered a new TPS from Ebay, and hopefully i can confirm the fix... But for those who sometimes experience a sticky throttle, I would check your TPS now!
Did you consider the throttle body might be sticking? If it's sticking open, the TPS will record "weird" numbers like that, when in fact it's working fine as the TB is stuck open.
I've never seen this problem with a tps, nor can I see how it would be even possible. Ive adjusted a tps by ear once, and turning it fully one way or the other did not result in the car zooming off like you describe. The worst thing that happend when misadjusted was that it idled high and being an automatic in this case it also crept forward by itself but not so fast that you couldn't stop it. I'd suspect a sticking tb aswell...
Here's the tech article. very easy to do and probably your culprit. If your TPS was faulty, the TB's would still be closed when you take off the accelerator (as they are mechanical), so there wouldn't be enough air going in to get the car to put on power and take off like that. http://www.pexcom.com.au/z32cms/e107_plugins/content/content.php?content.230
All a TPS is does is indicate to the ECU where on the fuel table it should be taking it's values from. It in no way controls your throttle position. Throttle Position Sensor , not controller (thats your foot). Look elsewhere and follow the above suggestions re: cleaning your throttle bodies out. A buggered TPS will give high idle, lean running or rich running (depending on how it's buggered) it won't open your butterfly's for you.
Yeah totally agree If the tps is faulty all it should do is richen the mixture and flood the car. Sticking full throttle like that would probrably be mechanical. Could still be throttle cable, ie. if they fray it can be getting stuck inside the casing of the cable and no amount of lubricating will fix the problem, or as has already been said could be gummed up tb's. Just my 2c worth
Ah... thanks for the replies guys... Lemme explain the current behaviour: I dont think its the throttle butterflies, but i could be wrong. On the actual engine i can see the throttle is completely closed. Thats why i discounted the cable theory. Nothing is holding it open unless the butterflies themselves are twisted compared to the outer linkage After the WOT incident, i pumped the accelerator several times with the engine off. WHen i restarted the engine, it was surging... revving to 3000rpm, then back to 1500, back up to 3000 etc about once a second or so. I figured it must be my TPS - telling the ECU the throttle is depressed, and to pump more fuel into the engine With the TPS off the car, and a multimeter connected to the pins, i can see that turning all the way to one side has a resistance of about 200ohms. Turn it a bit the other way so the resistance increases, and then back to the starting position, and the resistance is now about 250ohms. i.e. the resistance is higher than it was before Anyway, if this doesnt fix the problem then i guess i'll have a TPS for sale soon...
Fair enough...TPS may be causing your surging on idle...but the fact remains that there is no way that the TPS can cause your car to accelerate to a point where your smoking the rears up. Hell...some people can't even get that going with their foot to the floor.
Hahaha god i feel like a doofus. I thought "let me prove my theory for once and for all. I'll connect the 'faulty' TPS and turn the sensor manually to show the effect it has." connected it up and started the engine. No problems... Then i turned the TPS expecting the engine to start revving, but nothing... In fact the idle dropped at one point. Then i thought "huh?" and revved the engine a bit. Suddenly it was idling at 3000rpm... Check the throttle butterfly and sure enough it was stuck open. Funny thing was, it was REALLY stuck. I tried pushing it closed but no go. Opened it further and let go, and it stopped in the same spot. Turned off the engine and tried again and suddenly it closed all the way as if nothing was there... I'm guessing thats the effect of random bits of gunk in the throttle chamber. Unfortunately while mine is a VG30DE, the throttlebodies are side-on, and the only way to get to them is to remove a bunch of tubing and other stuff.. Shall be a fun task... D'oh! Anyone want to buy a brand new TPS? Should be here tomorrow or the next day. Will sell for $40 + postage (i paid $46 inc postage from Ebay)
Open the bonnet and manipulate the throttle linkages by hand through the centre cover on the engine. Then you will see if the throttles stick open. Might help to determine if the problem lies in the cable or somewhere in the linkages to the T/bodies or the throttle plates themseves. Also, get a second person to open the throttle with the gas pedal while you watch.
Omg.... Ok... this has got to be one of the stranger things i have seen So i started taking it apart. This is what i was faced with. Notice the throttlebody on the right is blocked by those hoses. Nevermind, one at a time... After removing a few of the hoses and loosening some bolts, i was able to wiggle the closer throttle body hose off. But whats this i see in there? Yes, thats right, a bloody rag! Fresh with markings showing how it was getting stuck in the throttle butterfly: Ok. so there ends the saga of "why my throttle sticks open sometimes." Probably explains the lackluster performance too... Will go for a drive to check now.
I'm actually surprised it ran...the beauty of twin TB eh? Remember to always take your rags out...ladies you too, it just dosn't work the way it's supposed to otherwise.
That's insane. Guess it was TB sticking after all lol. Maybe you need to replace your air filter, doesn't seem to be filtering to a fine enough level
This engine was put in by my mechanic 2 yrs ago. I suspect the rag was left over from when the engine was sitting on the garage floor. I will be having words to him this weekend, thats for sure! Explains why it only happened at full throttle too.. cos thats when it would be getting sucked into the throttlebody Strangely, removing it doesnt seem to have improved performance at all. Damnit, i guess it is just a slow barge. :bash: I did get a chance to get right in there and tidy up though (and confirm that there wasnt another one on the other side). The surging is still unexplained, but it hasnt come back so i am going to pretend it didnt happen.
Wow. That's scary... Glad you took the time to find it. Another thing, if anyone else finds their their throttle sticking open when they take off, the first thing you do is wack it into neutral and then brake, rather than brake against the force and try and turn it off. It's easier to do, plus in a TT, getting the key out won't do jack if you have a turbo timer.
