Getting wierd results testing throttle sensor
 

I have drawn a diagram in MS Paint to help visualize what I'm saying.

[IMG]http://i45.tinypic.com/33b0foo.jpg[/IMG]

I am getting a check engine code for my narrow range throttle sensor and after some testing, I am puzzled by the results. Also I replaced the throttle sensor with a brand new one less than a year ago. All measurements are with the multi-meter on 20K ohms. And it's an S5 NA.

When testing the resistance at the throttle sensor plug the resistance is within specs. However since i have a engine code i decided to test a few other things. If i plug the sensor into the harness and back-probe the harness side connector (the narrow range wires), the resistance is as it should be up through about 1k ohms and then it starts dropping back towards zero.

So that's where I'm lost. And for good measure I checked the voltage for the narrow range sensor at the ecu, and this was out of spec. However i checked the voltage reference wire at the sensor and the voltage there is correct.

I really have no idea where to go from here. Any help would be greatly appreciated.

Was the engine fully up to temperature? Matters

Yes. That it was. And another thing that happens and actually relates to what u said is the until operating temperature is reached, it has a surging idle. I thought that could be because of a vacuum leak and it trying to compensate by adding fuel. But i found no vacuum leaks.

Let's say the engine is fully warmed up. Then you take a sewing needle and prick the insulation on the green/red wire on the harness side of the TPS connector. Is the reading in the range of what the FSM says in the Control Unit pages? Engine idling is preferred.

I tried that with a pin or needle. Not sure if you mean measuring resistance or voltage. Assuming you mean warmed up but not running, as far as resistance yes, in idle position it is within specs. However as you slowly start to sweep the throttle towards WOT it hits about 1k ohms and starts decreasing. As far as the voltage reading on the G/R wire, it was within the specified range at idle and i believe at WOT as well but would need to recheck to confirm that.

I'd check the voltage with a hot engine. The resistance problem sounds more like a meter reading problem. Like a self ranging meter problem. On the wrong scale of the meter? Or the reading changing from K ohms to ohms?

Do it with the TPS connector connected.....hot engine......needle prick of the green/red with engine idling..........volts dc. If it's in the range of the Control Unit page of the FSM and the voltage goes up as you open the throttle and goes up in a straight fwd manner to ??? 4.5 to 5vdc...........it's good and go do something else to occupy your time.

I agree with Hailers that you shouldn't be obsessing about TPS voltages until you've tried the "normal" diagnostics for your problem, which seems to be a surging idle. Perhaps you've already done this, but start by setting the TPS with a check lite. How did you verify no vacuum leaks?

narrow range TPS should read .75-1.00 volts with the engine warmed up (fast idle cam down)

Thanks for the input guys. I'll check the voltage like you said Hailers. And cone crushr thanks, I'll try making a tps checker light. When I set it I just checked the resistance at the sensor to see if it was within range. Maybe not the right way, so I'll try with the checker light.
And I'm not 100% sure there are no vacuum leaks, but it tried two methods. 1: The use of throttle body cleaner around in suspect places. And 2: My friend told me to try this, Get some dry ice, get a bucket with a lid, make a hole in the lid for a vacuum line and run it into the bucket. Throw your dry ice in there and pour in some water, put the lid on tight but not too tight (we don't want a bomb), and run the vacuum hose in the bucket to a vacuum nipple on the car, thereby somewhat pressurizing it with fog. And hopefully it will seep out of any vacuum leaks. A sort of gheto evap smoke machine. Anyone have any input on that idea?

And arghx, thanks for posting that. I'll check that when i can.