I have a major problem - the TPS signal on my Ms2 install on my Mx5 has gone mad , fluctuating all over the place , even with the TPS disconnected and the engine switched off . It is totally undrivable , problem is I am trying to get home from the MOT (which it passed)
I have no idea where to look - its running screened cable already , and there are no loose or damaged connections .

Is the MS screwed ? Or is it something simple ?

Check the grounds and the 5v feed. My money is on a bad ground

Earths were the second thing I checked - and all good . Thing is - with the TPS disconnected , the coil unplugged , and the engine switched off , it is still showing a varying signal , and when tested running , it jumps to anything from minus 200% to plus 1000%................
It ran fine all the way to the MOT , ran fine during the emissions check , then started playing up on the drive home .

Are the other senders that get 5V still stable? Sounds like it's the signal wire touching 12V intermittently. Is it doing it even when nothing is moving? Is there a short maybe where the wires are soldered to the 37 way connector?

The other sensors read OK - I'm beginning to think the Megasquirt is the problem
This one was built by Chris for his KLMX5 project - which ended up being scrapped partly because it just wouldnt run right - could there be an internal fault which didnt show up on a stim ?

[Edited on 21/10/12 by clairetoo]

Unlikely but not impossible. Have you tried shorting the signal line to ground and seeing if that stabilises the dodgy readings. If it does it's less likely to be the squirt.

I have had this happen once before but it happened on a couple of sensor lines and was very visible in logs, a re-flash of the firmware cured it but I was fortunate to be sat in my drive at the time.