Nope, no codes. MIL is off.

 

Boi-
You can connect and trend chart multiple parameters on the same chart, right? So, find the correlation with the load going crazy and a bad sensor and I bet you have it!

 

How would I do that? I'd love to have datalogging capability like Megasquirt has. I have a generirc scan tool, plus a Mongoose tool and laptop with SDD/IDS that I can have connected as I drive. I didn't notice a datalogging function in IDS, but it's a pretty clunky interface.

I was looking at the JDHT CD further last night, and I noticed under TPS: "When faults are present, a default value of the throttle position will be supplied which will be one of two values using estimated manifold pressure. High manifold pressure will cause the default to be a high value of throttle position which will indicate full load, otherwise default will be a mid-range value of throttle position. While fault counting is in progress a backup value of throttle position will be supplied, which is the last valid value."

One cause of a high TPS reading is ground harness open circuit, so I'll start looking at that.

 

IDS will certainly do trend charts and YES, it the interface is worse than clunky. I can't remember where it is, but there is a parameter charting function there some damned place.

I would have thought you would get a TPS code by now if you had a TPS problem, and I would not expect the harness to be the first place to look. I would get a DMM anf test the TPS feedback while rotating the throttle to check for smooth transition between about 0.5 and about 4.5 volts. And I would sure try and figure out how to get connected to do the TPS calibration because you will need it if you replace the TPS.

 

I was surprised not to get any airflow codes when the AFM was disconnected, but I didn't.

I'll see if I can get IDS to connect and do the TPS calibration. Last time I connected it wouldn't pull in the car spec because it couldn't connect to the security module and ground to a halt at that point. Perhaps a momentary open circuit causes the TPS signal to get corrupted and then it makes contact and works again? Loose wire, broken wire, bad connection somewhere? It never does this when cold, only when hot, so perhaps something expands?

 

Potentiometers could display that behavior.

 

An update to the original problem. After driving with my scan tool plugged in, the car would stall as the reported load would go to 97%, when I hadn't moved the throttle from the 18-20% it was at. The ECU would then fuel for full throttle, and the car would die as it was flooded.

After much reading of the technical documentation, the only thing that reports load is the air flow meter. I located another AFM on ebay UK, and just for good measure I changed the ECU as well; since the ECU could have been damaged when the PO tried to jumpstart the car and reversed the polarity on the connections. Just in case the wiring harness was damaged, I also made up a new harness to run directly from the ECU to the AFM.

I've spent 2 days driving the car and so far it has behaved well. Interestingly, the ABS fail and trac fail lights have gone out and have stayed out, so I suspect the ECU was damaged. I'm cautiously optimistic the car is fixed. I'll keep driving it and see what happens.

Motto of the story: don't buy a car where the PO has tried to jump start it the wrong way!

 

Please keep us posted. I have been following this and can't wait for the next episode.

 

Hi just wondered what the outcome was????

 

Sorry to not have posted the conclusion. In the end both the AFM and ECU was bad. I changed both of them and the problem went away.

My clue was driving with the trip computer showing instant mileage. I could be driving through the neighbourhood and it would be showing 35-40mpg at a steady 30 mph, then drop to 2 mpg and then car would then stall. One time it did that and I floored the throttle. The car stuttered for a bit, then picked itself up and accelerated quickly.

It seemed that both AFM and ECU were defective and were operating in a default mode. Most of the time it worked, but occasionally conditions were right and the holes in the Swiss cheese would line up and then it would stall.