Wandering TPS idle hard switch

[madkiwi]

I thought I had resolved my TPS issues last August. When I figured out last year the TPS was intermittently opening without touching the throttle I though the switch was bad, so got a new one (genuine Nissan). I had set the adjustment, and it seemed to be good for a few months (I'm in Montana, car is stored from Nov. 1st until the end of February).

Had some problems earlier this year, and wondered if the problem is not the TPS at all, but that I have a bad connection between the TPS and the ECU. Looked at the hard idle switch connector, it was really corroded. Purchased a new pigtail, installed it about 3 weeks ago. Still having minor issues, then Friday when I was heading home the engine was idling at 1500 rpm. I had the laptop in the car with me, and the ECU data connector was in the glove-compartment so I hooked it up.

Not touching the accelerator at all the idle switch was off. Tapped the throttle a few times, but the idle closed switch stayed dark, in other words- open. Too hot to do anything with it, decided to deal with it Saturday.

Thinking, what's left? The wiring harness itself. Figured somewhere between the connector and the ECU, I have a broken sensor wire.

I pulled the connector, and jumpered the idle closed switch so the ECU would see it. Started twisting, pulling, flexing and wriggling the harness. Nothing. Idle closed circuit stayed lit. Squeezed the harness all the way down the wires to the main loom. Not a problem, hard idle light in the software didn't even blink (Using OBD Scan Tech). So that theory is disproved, my wiring is good.

Reconnected the harness. Voltage at idle was 0.42 volts, idle closed switch showing same. Loosened the TPS screws, started moving it around. Pretty soon I had some weird s*** happening. After rotating it the full amount of the adjustment a couple times the idle switch only lit up at 0.16 volts, way out of spec. I did the adjustment as detailed on the Z32 Wiki- rotated the TPS until voltage was good (0.44 volts) then unplugged the oval position sensor connector for about 4 seconds until the hard idle switch turned on. Then re-connected the position connector.

Drove the car Saturday, idling was great. No fast idle at all. With the AC on she idled around 1000, without about 800.

But for how long? I had thought this was dealt with before, and the problem came back. Why does the TPS hard idle switch wander out of spec? Adjustment bolts are cinched tight. WHAT AM I MISSING?

Frustrated in Montana...

[rgregoryb]

Leave the multimeter hooked up and while idling lightly tap the tsp with a rubber mallet or something similar. Mine was doing what yours was and by tapping on it I saw the voltage bouncing all over the place. Just because it is newer doesn't mean it can't be bad.

[RubyRed300ZX]

Agree with the madkiwi. Few years ago, I went through 3 brand new TPS sensors. Two out of the box were bad. Dead spots throughout the range. Three different "manufactures", yet, all three looked identical. Nissan certainly never made their own TPS. What I did find identical on all three TPS sensors was a gold colored small label affixed to one side of each of these TPS sensors that read "Made in Italy." Same identical label, three different "manufacturers." Reasonable guess here is that Nissan sources there's through the same manufacturer... one with very poor Quality Control.