MacGyver

I'll have to check the wire colors... I know it was the lower two wires when standing in front of the car. From the description given, it sounds as if it was the ground and output wires (as expected). I use a multimeter for measurements, not a scan tool. A scan tool was used originally simply to pull the CEL code, nothing else.

I'm aware that the ECU reads voltage, not resistance, but the resistance is what creates the voltage drop that is read by the ECU, so measuring that is half of the battle. True, though, that it doesn't give the whole story... I'm willing to bet the sensor is not seeing the entire 5V, as well, based upon the lack of a near-5V value at the output during WOT.

Tracing the wiring back is going to be a butt and a half... I certainly don't relish the job, but I'll do it to save the money.

There's always the possibility a wiring loom was screwed up during my accidental off road trip a few weeks back, shortly before this whole mess started. I don't believe the looms travel too low in the engine bay to get caught on debris (unless it REALLY got up into the engine bay), but I'm not writing the possibility off.

I'll go out in a few minutes and check it all again... let you know in 10-15 minutes.

alexf20c

MacGyver, I would first check your ground side before you rip your wiring harnesses apart. Just check ground to battery voltage and see what you get.

The reason I mentioned resistance is because like you say, it's only half the story. If you're not getting full voltage in the first place (from either a short to ground or high resistance), your resistance values will be off as well.

As for the scan tool (and/or scope), it's not a must, but it's nice to have. You get much more detailed patterns, and you almost need it to diagnose a faulty TPS.

MacGyver

The reference side shows a healthy 5V (+/- a few tens of millivolts, didn't pay that close of attention to it). At WOT the output shows 4.30V, at idle the output shows 0.08V. I don't know the specific range, but the high value sounds reasonable... don't know about the low value (I would expect it to be a bit more, say a typical 0.5V). The current at WOT calculates out to about 0.9mA... plugging that back in at the idle resistance and the voltage should be what I expected, about 0.58V... but I only see 0.08V on the car.

Ground pin to car ground shows 24 ohms resistance (didn't measure for any voltage potential between the two, though). That seems pretty high to me, but I cannot say for sure as it will depend on the circuit topology... if it's a floating ground or differential signal scheme for noise resistance, that value is fine.

alexf20c

I misinterpreted the DTC. The P0122 code for "TPS Low Input" means the signal voltage is out of range, not the reference. Both readings (at idle and WOT) are lower than they should be - that's what's throwing the code. And the low signal voltage at idle is what's causing the choppy idle.

Try to mess with the TPS to get both readings to go up. Normal range for a 5v 3-wire TPS is 0.50-4.80v, or just about 0.50v higher than the readings you have now, for both high and low.

Slows2k

The closed throttle V's needs to be .5V or something really close, say .48-.53V. loosen the screws on the TPS and move the sensor through the adjustment slot's range untill you get something close to that. Then recheck the WOT V's

MacGyver

This sounds like a reasonable plan of attack... shouldn't take more than about 30 minutes to readjust everything. I'll let you know what I find.

MacGyver

OK, readjusted the TPS again. The idle reading is 0.53V and the WOT reading is 4.70V.

Seems to do fine while cold (ECU giving it extra gas), but once warmed up she lugs at 800-900 rpm for idle. The situation has improved slightly, however, as a quick rev of the engine will see the rpms drop really low (400-600 rpm), but it wouldn't stall (once it seemed like it was really close, so I tapped the gas... my battery was getting low, so I let it run for a while to make sure I could still start the car later).

I did not reset the ECU this time around, so I don't yet know if it is still throwing a CEL. My guess would be no as this is what happened when the new TPS was first installed.

Slows2k

Pull the back up fuse again and let the car idle for 10 minutes with no other electrical loads on. This is the "idle learn" should be fine after that.

alexf20c

You need several closed loop driving cycles to fully reteach the ECU, though, and that can take awhile. I would just clear any codes, and see if it throws another code and the CEL. Then go from there.

By waiting for a CEL, you can narrow down the possibilities.

MacGyver

I'll reset it tonight, but I have an appointment at Honda early in the morning, just in case. If it seems to clear up while driving there, maybe I'll reconsider, but we have another hurricane bearing down on us, and I can't afford to be without a smooth running car any longer.