Qh: Trans Oil Temp On 5sp?

If I had to guess, the most common sensor to wire into an unused lead is a wideband (though usually people use the egr input, but if you have a functional egr they may have used the trans temp). Does your car happen to have one? The rapid switching you're seeing looks kind of like a nice o2 sensor narrow-band output. The software of course is just seeing voltage and converts that to a temperature reading.

As Noobz mentions, you'll want to find the pin / color of the lead coming from the ecu to trans-temp. Then figure out (physically) what's connected to that wire. Look for anything aftermarket, as I mention o2 sensor is a prime suspect.

For your high idle, you're correct, you should be able to get it down to ~650 with IAC disconnected using the throttle adjustment screw. If you can't, you might want to adjust the idle air bleed screw (allen screw under the plug on the throttle body, turn it in to give it less air). If still no luck, check to see someone hasn't drilled holes in the throttle plate. Otherwise, you're probably dealing with a vacuum leak (you mention you've checked, but the brake booster could be leaking, or you could have a pcv plumbing problem if someone['s added breathers, the evap bleed line is also commonly a problem on our cars), which could also explain a poor idle and those high-spots on the graph where the ecu is putting in more fuel because it thinks you've gone lean (assuming that's an o2 sensor output).

lizzard said:

thanks for you answer. when I unplugged the cable which is connected to MAF and ACT, it stopped up to 98% with this switching signal, another 2% are still switching somewhere else. so I have to go further with my examinations.
the other problem is, that I have a crank ok no start issue. maybe because I touched one of this 20 year old wires which are a real PITA.
but jrichker has a checklist I will work through the next days...

however, I wish u happy christmas!

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A very merry Christmas to you too! Just an FYI, if you unplug the MAF & ACT, closed loop is disabled, so you'll no longer see the o2 sensors switching (they'll remain at a steady voltage). I'd still bet you have an o2 sensor plumbed into trans temp.

jrichker's checklist is the best for crank & no-start, good find, and good luck!

I don't have an xdl logfile, sorry, hopefully someone else does (I replaced my QH with a Moates F3 chip until the next time I make hardware changes)..

lizzard said:

thank you guys for helping me
so, let's reveal the mystery of the trans temp oil data on a 5speed:
It ended up in pulling every wire from the ecu. I left only following 4 PINs:
1 keep alive power
20 case ground
37 vpwr
40 ground
no sensors, and even then it showed this strange signal!

so, I still don't know where it comes from, maybe from the PCM, the quarterhorse,ect
maybe the signal is of no further importance...idk

btw: the crank-no-start-problem turned out to be a fried TFI. But I was lucky and had a another TFI handy.
thanks @jrichker for your checklist!

...and I'm still chasing my idle problems, though the engine has no more vacuum leaks, it still dies very quick when I release the clutch...

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If you haven't done a smoke test for a possible vacuum leak you can't rule out that possibility. There are too many hidden areas that only a smoke test will reveal.