New O2 Sensor Changed Idle Speed

[cda951]

A really simple test would be to unplug the KLR and see if the problem goes away (key on, engine off, of course).

[Latitude48]

A really simple test would be to unplug the KLR and see if the problem goes away (key on, engine off, of course).

I'm not sure which "problem" you are referring to as there are a few issues. I already performed tests with the KLR disconnected.

Today I performed a test with the KLR and Throttle switch disconnected, and with terminals 4 & 6 jumped with a paper clip to simulate the closed throttle condition. Result: Mode = Idle, V = 2.95, which is the correct result.

At this point I do think my Throttle Switch has a faulty microswitch, but the KLR could also have issues.

[Tom]

A really simple test would be to unplug the KLR and see if the problem goes away (key on, engine off, of course).

I'm not sure which "problem" you are referring to as there are a few issues. I already performed tests with the KLR disconnected.

Today I performed a test with the KLR and Throttle switch disconnected, and with terminals 4 & 6 jumped with a paper clip to simulate the closed throttle condition. Result: Mode = Idle, V = 2.95, which is the correct result.

At this point I do think my Throttle Switch has a faulty microswitch, but the KLR could also have issues.

Where are you getting 2.95 volts?? Are you probing the DME circuit board? Or is that what the OBD+ is reporting?


Either way, with everything else hooked up (including KLR), does the idle return to normal (~840) when you pull the TPS connector off and jump pins 4 and 6 in the connector?

[Latitude48]

A really simple test would be to unplug the KLR and see if the problem goes away (key on, engine off, of course).

I'm not sure which "problem" you are referring to as there are a few issues. I already performed tests with the KLR disconnected.

Today I performed a test with the KLR and Throttle switch disconnected, and with terminals 4 & 6 jumped with a paper clip to simulate the closed throttle condition. Result: Mode = Idle, V = 2.95, which is the correct result.

At this point I do think my Throttle Switch has a faulty microswitch, but the KLR could also have issues.

Where are you getting 2.95 volts?? Are you probing the DME circuit board? Or is that what the OBD+ is reporting?


Either way, with everything else hooked up (including KLR), does the idle return to normal (~840) when you pull the TPS connector off and jump pins 4 and 6 in the connector?

Tom, I'm not measuring any voltages myself, the 2.95 volts is displayed by the OBD+ SW. Joe added this output so I could monitor the throttle switch voltage along with the mode displayed for the throttle switch. As I stated, Idle should be ~ 3 V, Off Idle ~ 5 V, and Full Load ~ 3.8 V. I get ~ these numbers with the KLR and throttle switch disconnected and ignition ON.

OK, I reconnected the KLR and left the throttle switch disconnected with the terminals jumped and I ran the engine. When it was cold it ran horribly with the idle fluctuating from barely running to something in the 8xx rpm range. During this time, the throttle switch voltage would swing back and forth between 1.9 and 2.95 V. The mode displayed was Idle. After the engine warmed up the idle speed was more stable, in the 8xx rpm range, the throttle switch voltage was 1.9 V, and did not cycle up and down. Interestingly, the ICV % Open was 115.5, which doesn't seem to make sense, but I don't really know the valid range for the ICV.

Not sure what to make of this test as the results weren't what I had expected. I suspect the engine doesn't like to run without a signal from the throttle switch potentiometer.

I don't think there's much I can or want to do until I get my multimeter on Tuesday and Joe chimes in with his thoughts.

BTW, any tips on the best tool(s) to remove the lower throttle switch screw? Not sure I have anything that will work in that tight area.

[Latitude48]

I think we have a "Eureka moment." Here's Joe's latest input:

"Hi Tom,

There is a possible failure mode where the idle contacts could emulate a "full load" state. Note that "off Idel" [sic] is the largest voltage of the three states. This means to transition from "idle" to "off Idle" the voltage must swing past "full load" at 3.8 volts to reach "off idle" at 5 volts. It is normal to see an occasional glitch of "full throttle" in the FocusOBD software when transitioning from "idle" to "off idle”, especially noticeable when graphing. Both my 944 Turbo and 944 NA do this.

What may be going on in your case is that when the idle contacts are closed the resistance between the contacts is higher than it should be, possibly due to corrosion or oxidation. If the resistance was just enough to put the “idle” voltage closer to "full load" than to "idle," the OBD+ module would interpret this as "full load," most likely the DME program would as well. Unfortunately, I do not know the exact thresholds the DME uses to trigger each of these modes, that is arbitrarily set in the DME program. It would take someone who knows the DME program inside and out to determine the exact values (and schema such as hysteresis) from the hex code. However, in theory, I could likely find this out through experimentation by connecting a variable resistor to the idle switch input and adjusting it until the engine changes behavior when transitioning between the three states. Another thing I could potentially do is calculate the "idle switch" contact resistance and issue a warning before it reaches a failure point. I will note these features in in the OBD+ firmware project backlog for a future update."

Ah, that makes sense! This scenario could also explain why the OBD+ can show the throttle switch in Idle mode the first time the ignition is turned ON with the engine OFF, and then when the ignition is turned OFF and back ON again, the mode displayed is Full Load. Although it doesn't seem logical at first, gaining this insight into how the system works does appear to show the OBD+ displays everything correctly based on the status of the throttle switch voltage. Seems like a finicky system!

[Tom]

I think we have a "Eureka moment." Here's Joe's latest input:

"Hi Tom,

There is a possible failure mode where the idle contacts could emulate a "full load" state. Note that "off Idel" [sic] is the largest voltage of the three states. This means to transition from "idle" to "off Idle" the voltage must swing past "full load" at 3.8 volts to reach "off idle" at 5 volts. It is normal to see an occasional glitch of "full throttle" in the FocusOBD software when transitioning from "idle" to "off idle”, especially noticeable when graphing. Both my 944 Turbo and 944 NA do this.

What may be going on in your case is that when the idle contacts are closed the resistance between the contacts is higher than it should be, possibly due to corrosion or oxidation. If the resistance was just enough to put the “idle” voltage closer to "full load" than to "idle," the OBD+ module would interpret this as "full load," most likely the DME program would as well. Unfortunately, I do not know the exact thresholds the DME uses to trigger each of these modes, that is arbitrarily set in the DME program. It would take someone who knows the DME program inside and out to determine the exact values (and schema such as hysteresis) from the hex code. However, in theory, I could likely find this out through experimentation by connecting a variable resistor to the idle switch input and adjusting it until the engine changes behavior when transitioning between the three states. Another thing I could potentially do is calculate the "idle switch" contact resistance and issue a warning before it reaches a failure point. I will note these features in in the OBD+ firmware project backlog for a future update."

Ah, that makes sense! This scenario could also explain why the OBD+ can show the throttle switch in Idle mode the first time the ignition is turned ON with the engine OFF, and then when the ignition is turned OFF and back ON again, the mode displayed is Full Load. Although it doesn't seem logical at first, gaining this insight into how the system works does appear to show the OBD+ displays everything correctly based on the status of the throttle switch voltage. Seems like a finicky system!

For what it's worth, the factory allowed for up to 10 ohms when testing the idle contact. Joe's theory may explain it, or may not, but illustrates the challenge of trying to replicate the status seen within another system like the DME. This reminds me a bit of when I was trying to code my own knock counter to replicate the knock counts registered by the Curtis counter. You can get close with effort, and super close with a ton of effort, but getting the exact results is an epic challenge. If there were any way to monitor Pins 2 and 3 of the DME (e.g., he produces the board, so he could add a monitoring line....), you could eliminate all guess work.

When parsing voltages to this level of granularity, reference voltages, clean grounds and common supply voltages can all throw off readings too. Ask me how I know.... Also, that fall-through glitch sounds like the job for a Schmitt trigger/RC circuit to me, similar to a hardware debounce. I'm an amateur electronics hack with no formal training, however, so I'm sure Joe is light-years ahead. I'm just spit-balling here as I'm drawn to this stuff like a moth to a campfire.

I admire Joe's work and think it's awesome he's doing it. It just sounds like he has some work to do to get these outputs accurate enough for use as diagnostic aids. Until then, they may be complicating the effort...



On your last paragraph, I think the status changes like that because the KLR itself produces a spurious (your word) voltage (~.85v) if you just turn the key off and back on without the motor running. With the Full Load pin under 1 volt in that scenario, that's probably close enough to ground for the OBD+ system to register it as Full Load.

[Latitude48]

Joe asked me to run another test. He wants me to leave the Throttle Switch disconnected and jumped, and to also disconnect the KLR, and then switch the DME circuit board from Turbo to NA. Doing this will take the KLR completely out of operation and the engine should start and idle normally. He wants me to record the data and send it to him for analysis.

For what it's worth, as I've stated before, with everything hooked up normally and the engine running I ALWAYS get Full Load for the mode at idle, and moving the throttle ALWAYS changes it to Off Idle. I have not run the engine in this mode with the software version that displays the switch voltage, but will to that.

It probably will be Sunday before I can run these tests.

[Tom]

For what it's worth, as I've stated before, with everything hooked up normally and the engine running I ALWAYS get Full Load for the mode at idle, and moving the throttle ALWAYS changes it to Off Idle. I have not run the engine in this mode with the software version that displays the switch voltage, but will to that.

Oh, I must have missed that. Hopefully that's just a glitch with the software, which would be my strong suspicion. Once you get the multimeter, you'll know....

[Latitude48]

For what it's worth, as I've stated before, with everything hooked up normally and the engine running I ALWAYS get Full Load for the mode at idle, and moving the throttle ALWAYS changes it to Off Idle. I have not run the engine in this mode with the software version that displays the switch voltage, but will to that.

Oh, I must have missed that. Hopefully that's just a glitch with the software, which would be my strong suspicion. Once you get the multimeter, you'll know....

Not sure it's a glitch if Joe's theory about the microswitch contacts having sufficient resistance to push the voltage close enough to 3.8 V so that it drives the system into Full Load. Hopefully, I'll find out with more testing and measurements.

[Tom]

For what it's worth, as I've stated before, with everything hooked up normally and the engine running I ALWAYS get Full Load for the mode at idle, and moving the throttle ALWAYS changes it to Off Idle. I have not run the engine in this mode with the software version that displays the switch voltage, but will to that.

Oh, I must have missed that. Hopefully that's just a glitch with the software, which would be my strong suspicion. Once you get the multimeter, you'll know....

Not sure it's a glitch if Joe's theory about the microswitch contacts having sufficient resistance to push the voltage close enough to 3.8 V so that it drives the system into Full Load. Hopefully, I'll find out with more testing and measurements.

Fair enough. Poor choice of words, I just meant if the OBD+ was reporting "full load" when the KLR isn't actually triggering that signal. If that's the issue, then I suspect the DME is better at weeding that out, otherwise the DME would switch to WOT maps when this issue occurs -- i.e., even though the KLR signal isn't triggering. My guess is your multimeter will confirm the KLR is not triggering even though the OBD+ says full load. To rule out the possibility of the DME being likewise tricked into running full load maps despite no full load signal from the KLR, a wideband would do it. When the DME is running off its full throttle maps at idle, the AFR drops out of closed loop and can get so rich the motor will idle terribly (not unlike how you described it when testing with the paper clip.... hmmm....).