Help with sporadic high idle

[Sla90lx]

This one is driving me nuts! I've been working on getting my VE table in line and making good progress but my idle will sometimes be ridiculously high when I come to a stop. I've just noticed today that when this happens the sensor data in TP shows idle mode to be off idle. My TPS data show 0.53 volts & tps% 1 or sometimes 0.51 & 0 with VSS @0, but IAC counts sometime as high as 100. When it does work properly, I've seen it go to idle mode as soon as VSS is below 4 and the IAC counts drop to 10-15. I have short logs of when it does both if anyone can help, this is a 7747 with $42 mask.

Thanks,Chris.

[EagleMark]

Post a log and your bin. Also what bin did you start with?

The TPS% is just a calculation from voltage in the $42 ADX file. There is no TPS% in data stream so don't get hung up on it.

But the TPS voltage is accurate and if it's changing? Have to fix that. Sticky cable? Worn shaft? Loose TPS? When key is turned on the ECM set's to 0% TPS based on voltage. So if voltage is changing then the ECM thinks TPS is open/off idle!

[Six_Shooter]

The '7747 doesn't auto zero like P4 ECMs, this is why the TPS is adjustable on vehicles that use the C3 style ECM.

[EagleMark]

I heard that somewhere too! Maybe a thirdgen thing? But none of the 7747 vehicles I've seen have adjustable TPS. And I made a hack to include TPS% in data stream to prove they do set to 0% after a throttle blade adjustment and then key on.

[Six_Shooter]

Odd, EVERY single 7747 and similar equipped TBI truck I have worked on had an adjustable TPS.

I've also had issues when the TPS was set just a tad too high as well.

[EagleMark]

Odd, EVERY single 7747 and similar equipped TBI truck I have worked on had an adjustable TPS.

I've also had issues when the TPS was set just a tad too high as well.

Really? I'd say it's a Canada thing but my truck was made in Canada and no adjustable TPS?

Long ago I read a post from Dimented24x7 that said TPS voltage was not an issue until over 1.0 volt... I did some testing with the TPS% hack so it was accurate from data stream and did find issues with anything above .74 so I don't even bother adjusting TPS voltage anymore unless over that.

Next time I work on one I'm going to revisit this though...

[Sla90lx]

Started with stock ASDU from this site. I thought that under a certain Tps, like 1.1.......Holly %@#&! I think I may have found the problem looking to tell you that value. How about "IAC TPS percent for closed throttle" being set at 99.21. Ha, that might have a slight effect huh? But then again why would it go in idle mode half the time?

Thanks anyway, hope that was the problem. Will find out in the morning,Chris

[Sla90lx]

Like I said, my Tps will set on either 0 or 1, so I don't think it zeros out. In fact, after setting my min air I had to move my TPS. I enlarged the holes not enough the first time and went back to make them larger.
In between that I disconnected power every time thinking the ECM just needed to clear out. the first time I did that it came back up with the same value of 3% throttle. The second time around I realized the washers on the bolts were up against the TPS stopping it from moving. Once I cleared a little room for them I was able to get it set to zero.
Chris

[Sla90lx]

Okay, scratch that. I must have some how keyed that in when I pulled it up. I went to close the window and it asked to save change. I said no, reopened and it's set at 1.17. So it looks like I still have a problem(besides being a dumb a$$!)

[EagleMark]

The TPS% is just a calculation from voltage in the $42 ADX file. There is no TPS% in data stream so don't get hung up on it.

Read ^^^ this ^^^ !

"TPS from hack" is not accurate unless you have applied the hack to the bin being used during datalog.

TPS% Calculated from voltage is not accurate, just a calculation from voltage.

[84Elky]

This one is driving me nuts! I've been working on getting my VE table in line and making good progress but my idle will sometimes be ridiculously high when I come to a stop. I've just noticed today that when this happens the sensor data in TP shows idle mode to be off idle. My TPS data show 0.53 volts & tps% 1 or sometimes 0.51 & 0 with VSS @0, but IAC counts sometime as high as 100. When it does work properly, I've seen it go to idle mode as soon as VSS is below 4 and the IAC counts drop to 10-15. I have short logs of when it does both if anyone can help, this is a 7747 with $42 mask.

Thanks,Chris.

It's possible the VSS signal to the ECM is > 0 MPH when the problem occurs. That can occur with loose wiring, poor ground, etc. Bottom line, for most OBD1 ECMs VSS must report absolutely 0 MPH or will not be considered at idle. The fact that is works sometimes and not others indicates a possible inconcistent VSS reporting issue to the ECM. Additoinally, most code has a minimum TPS value that determines when idle is being considered. Might check that value. For example, for '7730, it's 0.78% and below.