How does the TPS work?

[marakka]

How does the TPS work? *LOL* I mean.... what does it do? Is it a potentiometer (sp?) and just pushes out voltage as the thing springs open? Or is it just an open closed switch?

I'm wondering this because my car is "bucking" at high RPM's but before the limiter. Something like 4k or above it will buck hard until you shift or let off the gas and go below the RPM range.

[AdamF 88iS]

It is just a swtich. It clicks for idle and wide open. There is nothing in the midrange.

[bimmer8604]

the E30 TPS is a switch, not a sensor. That means that its an on/off signal. At school we got to hook up an oscilloscope to it and see that when its closed it sends a very low voltage, but when you open it it jumps to 4-5 volts. Im sure you can use a mter to check, and just backprobe the sensor. You have to look for the ground wire, the 5+ always on signal, and the signal back to the computer. If you are having problems with your car stalling and running rough at a specific RPM i would check like your CKP, or make sure all your ignition stuff is on correctly. Have you disconnected your battery lately? Sometimes when you drive around for a while your car will learn your driving habits, and will learn the car(aka sensor wear, barometric pressure, always WOT..etc...) and when you unplug your battery you loose that KAM(Keep Alive Memory) and it will take a while to relearn.

Thats a lot of info, but HTH

Kyle

[Madhatter]

Yes you are right, there is such thing as a variable resistance TPS, and yes it is essentially a pot. All it does is change the resistance as the throttle moves which changes the voltage.

But you are wrong in that the E30 doesnt use one, it's a switch as people have already explained. Thats why megasquirt guys cant use them :)

[marakka]

Well shit.... this is drivig me nutty. I can't race my car. I'm in first.... I mash the gas and it goes fine all the way to redline. I hit 2nd and mash it.... and it starts bucking hard on me. Let off the gas and it calms down and I smoothly floor it. Its fine sometimes to redline.... sometimes to 4500 rpm. The same with 3rd 4th and 5th. Yesterday I could drive the car to 160kmph and it would be fine then woudl buck. I'd slowly let off the gas and smoothly and slowly push it past 160hmph and it would do ok. Then it would pick back up at 180kmph. Got to where I'm going and shut it off to go inside. Came back out and viola.... it went to 200kmph and then started buckinig. I've replaced shitloads of stuff trying to figure out what this can be, but its driving me nutty trying to find out. I'm guessing it still could be the TPS considering the rpm ranges its happening at and the speeds also..... Thanks for the input guys.