G50: Lino's 91' Q can't set TPS, Idles at 1100 RPMs/AAC 76%

[Infinitiguy19]

Lino told me about a problem that he is having with his car (1991 Infiniti Q45). Basically he has replaced the Throttle Position Sensor (TPS) because the old one was defective. After replacing it he has not been able to set it to .44 Volts (Dennis-Q45Tech says thats what it should be) (.40-.50 Volts is normal according to the FSM).

I told him to make sure the car is warmed up to at least 176*F (80*C) or more when setting the TPS. Because even though the coolant temperature sensor (As read with a Nissan Consult/Emulator or a multimeter) may say 176*F (80*C) the Fast Idle Cam (FIC) may hold the throttle open a little bit still. And thats enough to throw off the TPS. I also told him to make sure to have the car off and the throttle closed completely (Cable not holding it open) or a midget in the car holding it open to ruin his day.

So with the above covered he should have been able to set the TPS, right? WRONG! He did the above and his car still idled at 1100 RPMs with the Auxiliary Air Control valve/Idle Air Control Valve (AAC/IACV) bypass screw all the way turned in. For some reason the AAC/IACV was working at a 76% Duty Cycle instead of the normal 10% or less. When the AAC/IACV is unplugged the vehicle returns to a normal idle of ~650 RPMs with the TPS set to .44 volts.

His intake was cleaned fairly recently and to be sure I had him disconnect the AAC/IACV electrical connector and turn the AAC/IACV bypass screw all the way in and have him read me the engine idle RPMs. He said it idled at 450 RPMs and that is pretty spot on as the holes under the throttle plate when completely closed only allow enough air in for the engine to idle at roughly 450 RPMs. The AAC/IACV bypass screw only adds 100 RPMs when set at 2.5 turns. The AAC/IACV duty cycle at idle when clean when at 10% add another 100 RPMs to the equation which equals 650 RPMs.

No codes are reported when the TPS is set to .10 or turned all the way in one direction I forget which one he said. I also for the hell of it told him to clear the Self Lean (Mixture ratio) in the hopes that would help.

I know my Q45 Control Unit logs online comparison topic was a failure as was the new software I want to make for the Q45 topic a failure as well. But please don't let this one be a failure because its not really going to help me as much as its going to help Lino.

So any ideas as to what the problem could be?

Oh yeah I think I saw Bow Wow use a Nissan Consult 2 on the Ford Mustang when they were still building it to race (Near the end of the movie) in The Fast and the Furious 3: Tokyo Drift.

[Q451990]

I would try disconnecting the battery for a few minutes and then try it again. I have chased an intermittent problem with both of my '90 Q45s that is similar, but it only crops up about once a year. The car idles high unless you unplug the IAC valve. Usually it will clear up by turning the car off and restarting it. The last time it happened was almost two years ago - and I was actually able to get it plugged in to my laptop consult for the first time. If I recall correctly the "Throttle Closed Switch" wasn't reading closed at idle - but I don't really remember for sure. I wrote down a bunch of stuff on a napkin that was in the door pocket but didn't make a clear note about that.

Heath

[Infinitiguy19]

So your saying the new OEM Throttle Position Sensor (TPS) might be defective? Thats not unheard of but it is unfortunate.

Lino so I don't forget set the TPS to .44 with the car off and with a coolant temperature of 80*C (176*F) or higher. And tell me or post back on NICO if OBD Scan Tech Nissan reports the Closed Throttle Position Switch (Idle Switch) to be on at idle and off when the throttle is opened.

[lino]

I have swapped out 3 used TPS switches and now have a brand new one on the car. All of them behave the same.

[Q451990]

So your saying the new OEM Throttle Position Sensor (TPS) might be defective?

No, I'm saying there's a glitch in the ECU not recognizing it - or a wiring or connector problem. This is just a theory though... what I'm really saying is to check to see if that switch shows "closed" at idle with the laptop consult.

Heath

[3Q Jay]

Lino- are you reading TPSvoltage from thelaptop? try reading it at the TCU with a DVM. As Paul said, try with key ON engine OFF warm engine first.

Also, make sure you get a linear progression from 0.44v to >3.6v at WOT.

[NewKleer]

yes ive heard of a similar issue - ECU not registering throttle closed, so its idling higher because it doesnt think it should be idling since throttle isnt closed.

get latest ecutalk and get log of TPS and all the throttle switches whatever they are (maybe just the single 'clsd throttle' one and see if it changes when throttle open/closed.

if u cant get 0.4v or whatever then something is wrong, either mechanical with the TPS or adjustment, or electrical, e.g. power/grounding to the TPS.

[Infinitiguy19]

Heath,

Makes sence.

Jay,

Lino is using a ECU Talk Consult cable and is using ECU Talk to read the Throttle Position Sensor (TPS).

NewKleer,

Lino set the TPS to ,44 volts well as close as he could at least because it would go to .46 volts every couple of seconds or so with the throttle closed. When set at .44 volts the closes throttle potions switch did not activate, ie: the ECU didn't know the throttle was closed. After setting the TPS to .44 volts (Coolant temp at least 176*F, 80*C, Key on) is there any other procedure needed to get the TPS to know thats what the voltage is at normally when the throttle is closed?

When he set the TPS back to .24, turned all the way back the closed throttle switch would register as on ie: the ECU knew the throttle was closed. But only when the throttle was opened to .30 volts and above did the closed throttle position switch register as off.

[NewKleer]

not sure on the mechanics of the specific TPS but id try adjust it then to .24v (where switch was working) and see if that helps (if idle is high AND AAC is high then ecu still isnt wanting to idle). if its auto check park/neutral switches working.

[Lokim]

Unplug the ECU and ohm the TPS via the ECU connector. Run a slow sweep w/ a DVOM and see what the readings are. If OK, bad ECU or AAC. If not, wiring problem.

[Infinitiguy19]

NewKleer,

The Park/Neutral AKA Inhibitor switch is confirmed working otherwise the vehicle wouldn't allow the key to be removed from the ignition or allow the vehicle to go into any other gear.

Lokim,

Dennis AKA Q45Tech says that the Engine Control Unit (ECU) doesn't see resistance (OHM's) it just sees the voltage.

The Auxiliary Air Control valve (AAC) could not be bad as its only doing what its told from the ECU. And it has been cleaned and confirmed working correctly as well.

The ECU and TCU Connector were recently properly secured on Lino's vehicle so hopefully if he give it another try at setting the Throttle Position Sensor (TPS) it will work.

Good luck Lino and thank you all for posting in this topic!

[3Q Jay]

Heath,

Makes sence.

Jay,

Lino is using a ECU Talk Consult cable and is using ECU Talk to read the Throttle Position Sensor (TPS).

NewKleer,

Lino set the TPS to ,44 volts well as close as he could at least because it would go to .46 volts every couple of seconds or so with the throttle closed. When set at .44 volts the closes throttle potions switch did not activate, ie: the ECU didn't know the throttle was closed. After setting the TPS to .44 volts (Coolant temp at least 176*F, 80*C, Key on) is there any other procedure needed to get the TPS to know thats what the voltage is at normally when the throttle is closed?

When he set the TPS back to .24, turned all the way back the closed throttle switch would register as on ie: the ECU knew the throttle was closed. But only when the throttle was opened to .30 volts and above did the closed throttle position switch register as off.

for kicks and grins, when the ecut alk sees 0.44 to 0.46 (yeh, 0.46v is close enuf to perfection), read the pins at the TCU (35 to36? can't remember)and confirm they are the same.
Set the correct TPS voltage first, then worry about getting closed throttle position sensor adjusted.

[Lokim]

NewKleer,

The Park/Neutral AKA Inhibitor switch is confirmed working otherwise the vehicle wouldn't allow the key to be removed from the ignition or allow the vehicle to go into any other gear.

Lokim,

Dennis AKA Q45Tech says that the Engine Control Unit (ECU) doesn't see resistance (OHM's) it just sees the voltage.

The Auxiliary Air Control valve (AAC) could not be bad as its only doing what its told from the ECU. And it has been cleaned and confirmed working correctly as well.

The ECU and TCU Connector were recently properly secured on Lino's vehicle so hopefully if he give it another try at setting the Throttle Position Sensor (TPS) it will work.

Good luck Lino and thank you all for posting in this topic!

Infinitiguy19 - I know the ECU sees voltage. What I am trying to establish is whether the wiring between the TPS and ECU is distorting the reading. For instance, if the TPS sweeps clean at the sensor, but the readings are different at the ECU, the wiring may be cross-shorted or shorted to ground within the harness somewhere between the TPS and ECU. There could also be a break in one of the wires, causing additional resistance in the circuit. If that occurs, the voltage that the ECU "sees" will not be accurate. Also, verify the 5V reference voltage at both the sensor and ECU, and check for continuity and resistance between the wires for reference voltage, signal, and ground with both connectors unplugged. Wiggle the harness while checking to expose any intermittent problems. This should tell you whether the reference line is shorted to signal, signal to ground, reference to ground, etc.