Patrick G

iTrader: (14)

This is wierd. Recently my car started doing something strange. When I would push in the clutch after driving for a while, I'd notice my idle was up around 1300 rpm (which is well above my normal idle speed of 850). I logged this and found out my TPS sensor was reading 2.4% even though my throttle was completely closed. That would bump my timing to the main spark table and raise my idle way more than normal.

Here's how it happens. I'll be driving along, let off the gas and the TPS reads 0% as always. Drive a little more then notice the higher idle and see that my TPS is reading 2.4%. I blip the throttle. Nothing. Still 2.4%. Raise the hood, see if there's tension on the cable. Nope. Throttle is completely closed.

I bought a brand new TPS sensor and swapped it in. Still doing it.

I swapped out my Nick Williams 90mm for another one...still doing it. WTF is going on? This is a total mystery to me that 2 different TPS sensor and 2 different throttle bodies would do this. What in the world could be causing my closed-TPS to jump from 0% to 2.4% right in the middle of driving?

RedHardSupra

iTrader: (1)

did you try resetting the TPS sensor? what kind of TPS voltage do you get with your foot off the gas completely?

MNR-0

PG,

Log your idle follower and cracker PIDS to check that they are decayed to zero when it happens. Also log AC airflow adders, fan adders etc.

Could be you have some airflow adder, which is cracking open the IAC (don't know if yours is ETC) or blade, either way adding steps. You won't get idle control unitl all airflow adders are zeroed out.

BTW, I caught up with J-Rod when he was in AUS at the LS1 Nats, a few weeks back. Wish he had more time so we could talk **** and glean more info. about what you guys get up to over there...

Patrick G

iTrader: (14)

Yes, I tried that. The voltage is .4 Volts when the throttle is completely closed.

When I start the car, the TPS reads 0%. It's after driving the car for a few minutes that the TPS sort of resets/re-indexes itself and the new closed-TPS reads 2.4%. Keep in mind, the throttle is completely closed, but the idle is raised (since timing goes from 18 degrees to 36 degrees). When I lower timing to 18 degrees in my main spark tables, the idle comes down. This is not IAC related. It is totally TPS related.

Patrick G

iTrader: (14)

Good point. I checked those too. They are zeroed out when this happens. Something is re-indexing the 0 point of my TPS while I'm driving and this has happen with 2 different TPS sensors and 2 different TBs.

EDS01SS

iTrader: (30)

Somebody else had a similiar problem on here.....try wiggling the wires at the TPS sensor and see if your readings change. The TPS connecter was bad on this other persons car

MNR-0

When did it start doing it? Has it always done it? Did you make a flash change and then it happened?

Check your main spark table, and cross-reference that with the actual spark realised during decel. and via the Histogram. 30+* timing is too much on decel - it will want to *hang* with no load and a converter pulling it up.

Try decreasing timing on your 0.04-0.08 rows in your main spark table to like 20*, and from 1400 down at 0.12 to 24*, blending it in up from there so you dont have huge spark swings causing *surging* on decel.

I am almost convinced it sounds timing related.

SShawn

iTrader: (6)

i agree check the fires for an open or short. if its not visible just do a resistance test from the TPS to the PCM. it wont hurt to check.

98SS2836

iTrader: (6)

check the connector, of just change it. Seems it is the only logical thing that can be wrong.

Patrick G

iTrader: (14)

OK, I swapped out the connector, and it's still doing it. It seems to reset my 0% TPS reference more often when I drive over very bumpy pavement. This problem is not throttle body related. The TPS is completely closed when the sensor gets whacked out and the idle is raised. Again, the high idle is due to the car thinking it's out of the base idle spark tables (18*) and in the main spark table (40*). When I lower the main spark table to 18*, the idle comes down close to 850rpm, even though the TB still reads 2.4-3.1%. Again, this is not a mechanical/linkage issue...it's electrical of some sort.

12secSS

iTrader: (30)

So when the TPS% is at 2.4%, what is the logged TPS Voltage? If it persists, try raising the TPS Idle Enable setting just above 3.2% and see what happens? I had an issue with a car similar to this, it would stay at 5% TPS, it was electrical related since the voltage (when it happened) jumped up from .52V (max value for 0% TPS). This issue is not exclusively timing related, but rather timing table selection related ... IMHO.

PS: Also, try a different computer ... just for ***** and giggles. I had an ECM go 100% TPS with the actual TPS closed. Turned out to be a faulty ECM, when I swapped ECMs the issue went away. Just an idea.

hellbents10

iTrader: (10)

Could be on the way to the ECM or the ECM itself. Seen it before.

Mike44138

iTrader: (3)

+1. Check the routing of the wires on the way to the TPS. They could be picking up induced voltage. Esepecially they're close to the coils.

mattsls1

iTrader: (22)

This has happened on my car before. I think it was because my battery was too low or something. When Ed Wright tuned the car he didn't mention anything about the tps acting up.

Patrick G

iTrader: (14)

Voltage was 0.4V at 0% or at 2.4%.

12secSS

iTrader: (30)

0.4V = 0%
0.4V = 2.4%


That is really f'ed up! I will look through my Helm's manual, I recall a proceedure to diagnose the TPS signal and associated control modules. Does your TA have traction control?

Patrick G

iTrader: (14)

If I had my scanner at higher resolution, I'm sure I'd see that one was something like 0.42V and the other was 0.43V. My TA has traction control, but the fuse has been pulled for over a year. This TPS problem just started happening a few weeks ago. Again, when the TPS reads 2.4%, the throttle is completely closed and the throttle cable has slack in it (so it's not the traction control cracking the blade or anything like that).

I have an EFI Live/Moates Road Runner for a PCM. It's been in the car for about a year and it's never given me a problem.

MCBRIZ28

iTrader: (2)

just a shot in the dark check connectors to ecm have been seeing corrosion under a few lately and could be picking up false signal from it.

Patrick G

iTrader: (14)

I'm checking all connections this weekend. I'm convinced it's some kind of electrical gremlin and most likely a loose or corroded connection somewhere. If I fix it, I'll definitely post back.

DrkPhx

iTrader: (15)

Something to check is the female (PCM side) connector pin. Over time, the metal tabs spread apart which results in less than ideal metal-to-metal contact with the male part. This can cause erroneous readings like you are seeing. This happened to me on the TPS and fuel pressure sensor.