Hey Guys, long time reader, first time poster. I'm hoping you all will have seen something like this before and can give me some information...

Okay... So I borrowed a Snap On Solus scanner and here's everything I found.

In the engine scan function, key on, not running.

TPS Voltage fluctuates from .8 - 2.54, bouncing wildly.
Throttle % 0 and 44, bouncing with TPS Voltage.

As I apply throttle, the TPS Voltage increases but maintains the 'bounce' up to 3.5 - 4.98 Volts and the Throttle % increases in relation to the throttle pedal but also maintaining that 44 jump as well. (10 to 54 up to 54 - 99 and then starts 'looping back as the 'low' part reaches 99%, the 'high' part of the jump hits 43%). The weird (yeah.. k.. weirder) part is I'm not at WOT. It hits 99% at about 3/4 throttle. If I mash further, the Throttle % reads 4 and sticks there. TPS Voltage does it's thing jumping around but Throttle % sticks at 4, now unresponsive to throttle pedal position. The only way to make it return to prior operation (jumping hi/lo of 44%) is to back out of 'live data', clear "codes" even though no codes are shown and then go back to live data, now the Throttle % is back to it's prior display of 0 and 44 (jumping wildly again)

NOW... I scanned transmission information and came up with this..

Transmission scan also shows TPS voltage and Throttle %

TPS Voltage reads exactly the same as the Engine Scan Function BUT
Throttle % bottoms at 44% and rises to 99% smoothly with the pedal BUT the scanner reads 99% before the pedal is at WOT (about the same as what the Engine scan showed). It shows 99% at about 3/4 of Pedal travel.

When cranking, the TPS voltage and Throttle % stabilize and read as what I would think they should read.

I bought a new TPS and put it on today because of the wild TPS voltage readings in the scanner and it made no difference.
I backprobed the TPS wires and it seems to be functioning perfectly.
Gray is 5v reference showing about 5.08V
Dk Blue shows .9V at 'idle' (engine off, key on) and increases in voltage smoothly to about 4.8V as I open the throttle.



I backprobed the TPS signal wire on the ECU and got the same readings.

SO.. Something in the computer is taking this information and showing very jumbled readings to the scanner.


The Bad.
I can't get the car to fire at all today. I drove it up and down the road the other day and aside from the shifting issue, it seemed to run pretty well (aside from the TPS readings I was getting... they were the same while the car was running)... but today, I can't get it to fire a lick.. It's getting fuel but I didn't get a chance to check spark, I was neck deep in messing with the TPS for now...

Does anyone have any thoughts on this?


One other thing I noticed in the engine scan section was
key on, engine not running
Set Idle Speed was at 3091 RPM. What do you guys make of that? Is that going to fluctuate based on other sensor readings or do I just have something completely effed?

Thanks again very much.. I really look forward to hearing with you all say..

I'm REALLY hoping it's just going to be a, "oh, you have a bad blah blah and that will fix all this"

 

What year is this LT1?

Just use a regular voltmeter on the blue wire for the TPS instead of the scanner and take your readings from there. It will be a much "cleaner" signal.

TPS voltage at idle needs to be anywhere from .2 to .9v @ idle, and the PCM will prorate the voltage from there (adding about 4v), so it looks like nothing is wrong with your TPS. I'd start looking elsewhere.

 

What i can't figure out is why the voltage is jumping at almost a 'set' amount in the scanner. it jumps about 10 times per second from .8 to 2.54 volts and rises at that same interval as I apply the throttle.

 

I never really relied on scanner data in terms of voltage when I could get the voltage directly from the sensor. As long as the TPS does what I mentioned in my first post when checking the blue wire, it's fine.

 

Oh, and it's a '94 TA (it's in the thread title)

 

...but, it is what the scanner sees that is the most important. Checking at the TPS with a meter does not mean those readings are getting to the PCM ok. Both must be in agreement.

Any jumping around of the TPS reading is a bad thing. Readings should be steady when the TPS is not in motion and smooth and linear when it is.

 

Cool, thanks for the Clarification on that, Rob.
And you know I don't expect you to spoon feed me info on both forums, I'm just trying to get as much info as possible.

But thanks for following it on both sites.

 

Anyone else seen anything like this?

I keep hoping it's a symptom that someone's run into before.

 

could a bad Idle Air Control be jamming up and causing the computer to try over and over to compensate causing the jumpy scanner readings?

 

Just curious if anyone else has any thoughts on this.
Thanks y'all