Crazy throttle

[Random_hero]

Just thought about getting everyones two cents. My MKIII 86.5 has got an insanely sensitive throttle and I'm not quite sure why any thoughts?

[Supra_Soul]

Try this.

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=101

[Dan_Gyoba]

Right. The TPS being poorly adjusted will cause some issues.

Basically how it works is this: When the TPS says that the throttle is closed (Whether it is or not) and the RPM is above 2000, the TCCS shuts off the fuel. So if you can have the throttle a little bit open and the TPS reads as closed, the car engine brakes, because there's no fuel. Then as you ease the throttle open, it still doesn't make any power, until suddenly the TPS reads off-idle, at which point the fuel suddenly returns. You get a sudden jump from no power to power.

Properly adjusted the TPS should show that you're off idle while the throttle is still very low, which will result in a smoother, less jumpy return to power.

Having replaced a TPS on my NA, and seen one go funny on another '89T, I can say that there's a number of things that can go wrong, here.

The sensor is basically a couple of copper contacts on the rotating part, and carbon traces serve as their contact pads. If the carbon pad for the IDL signal gets smeared, or some water gets into the TPS, the copper contact can make a partial connection to IDL at inopportune times. The result is that the TCCS puts you into fuel cut. Say the IDL carbon pad gets smeared just a bit, then the IDL signal will come on at higher and higher throttle positions, degrading gradually. Note than any non-infinite resistance from IDL to E2 is considered at idle to the TCCS, so even very high resistances will qualify.

A new TPS will cost you $40-$50 at your local Toyota parts counter. (I think mine was $47 tax in. It failed reading some 3k ohms from IDL to E2 at all throttle positions, which meant that with it plugged in, I could not get RPM over 2000.)

Ah. Here's another test that you can do to see if the TPS is at fault: Disconnect it.

The TCCS will not like this much, because it will no longer have load as part of its fuel map (DON'T go for WOT runs like this!) but it'll run more than well enough to see if this is the problem. With the TPS unplugged, the TCCS will assume that the throttle is off idle, but not at WOT. This will have a slightly gibbled fuel map, but the TCCS will then stay in closed loop mode, and not cut off fuel.

[Random_hero]

Right the tps is the throttle position sensor. and every place I found online wants a min of $100

[Dan_Gyoba]

LOL! I'll sell you the 2 year old one off of my NA for the $47 I paid for it. :) Okay. $40. :D Seriously though just give the dealers a call and ask about it. I can't believe that it'd have doubled in price since I bought mine.

[Random_hero]

Yeah I am going to call Ron and see what price.

[Dan_Gyoba]

Well, I'll tell you what, you can have my TPS for 1/2 of new price, though I suspect that it's cheap enough you might as well just go for new. I figure that for the amount that my NA engine will be running, I can live without it.

[Random_hero]

As of now I tested my N/A with the tps connected and it idles at about 1100 then I tried it after disconnecting it and same thing so I guess it is shot.

[Dan_Gyoba]

It's not the idle speed that will tell the tale, it's the response from zero to part throttle, particularly while engine braking.

With a bad, or poorly adjusted TPS, the car will suddenly kick, even if you SLOWLY get back on the throttle. With the TPS disconnected, it'll smoothly regain power. Well, more smoothly, anyway, since it won't be in FCO above 2000 RPM.

Test: Connect TPS. Coast in second gear from about 4000 RPM with the clutch engaged. At about 3000 RPM, start to slowly apply throttle again. Feel the kick as the engine decides that the throttle is far enough open to resume fuel delivery. Disconnect TPS and repeat. The response will be more gradual, but shouldn't be MUCH more so. This is because the TCCS will not cut off fuel at idle, because it doesn't KNOW that the throttle is at idle without the TPS connected.

[Random_hero]

Sry. I know it has nothing to do with the idle speed. I meant the same as in when I accelerate, I move the pedal an 1/8 inch and it revs extremely high. Also thanks for the test I'll give that a shot.

[Random_hero]

I dont know if this would be a related problem but the throttle is extremly sensitive just before the clutch is engaged. Like I said above that you press the gas down an 1/8 on an inch and it revs past 5,000. Is that normal? Also as well there is about an inch of free play on my gas pedal. Thx.