OBD 1 code 35 and idle at 2k (1 Viewer)

[AubieXX]

Been spending some time trying to track this down and not having luck.

I'm consistently getting code 35, even after disconnecting the battery for multiple days. It immediately shows back up. Engine runs fine other than the high idle. No other codes.

If possible, can you please make recommendations.

I've done what I think would be basic stuff like looking for vacuum leaks, replacing the EGR valve, new throttle position sensor.

1991 Land Cruiser with 240,000 miles.

 

[voodu3]

https://forum.ih8mud.com/resources/1991-land-cruiser-fj80-fsm-rm180u.218/

Download the fsm above thanks to @Malleus and go through the troubleshooting steps for the code and high idle. If you can’t find a solution there it’s possible the ecu is failing.

 

[AubieXX]

Awesome. Thank you.

 

[AubieXX]

https://forum.ih8mud.com/resources/1991-land-cruiser-fj80-fsm-rm180u.218/

Download the fsm above thanks to @Malleus and go through the troubleshooting steps for the code and high idle. If you can’t find a solution there it’s possible the ecu is failing.

Showing an HAC Sensor error with Trouble Area listed as ECU. From searching, I am seeing where 4 runners have an altitude compensation sensor or barometric sensor but not seeing one for a 91LC. Any thoughts on this, or am I looking at needing to replace the ECU.

 

[voodu3]

I saw the altitude sensor as the fault. I’m not too familiar with what sensors are on a 3FE. You might try checking with the 60 series guys
Unrelated to the code but have you checked the timing? It could cause the high idle.

 

[AubieXX]

Have not checked timing. Will try to do that this weekend and report back. I did see where the PO had previously replaced the ECU. Have another one coming from eBay.

 

[jonheld]

Very unlikely that the ECU is at fault here.
Looking through the EWD and FSM, the only reference I see for HAC is that error code.
I see no pins referencing that on the ECU pinout, the ECU schematic, or anywhere else in the FSM or EWD.
Personally, I have never heard of this on any 3FE and I have no idea where to start looking for it. My guess would be the AFM, but it's not mentioned anywhere.

Idle speed should be controlled by the ECU pushing the ISC valve to keep idle at 650rpm.
There should be slack in the throttle cable and the throttle plate should be resting on the endstop at idle.
All mechanical adjustments MUST be correct first as this ECU is 1986 technology.

 

[jonheld]

This is what I've found so far, but I have never actually seen one on a 3FE. Still not sure if this is a real thing or some sort of holdover from earlier models.
I got no hits after searching various VINs on partsouq for both FJ80s and FJ62s on "HAC" or "ALTITUDE" or "89464-35010" which is a part number that came up in a search.

"Diagram and location
Simplified diagram of the 3FE intake system
The HAC sensor is located on the intake manifold, next to the throttle body and other sensors. It is a vacuum-controlled sensor that works with the Engine Control Unit (ECU).
Specifics of the sensor's location
Sensor appearance: The HAC sensor is a small, round, or square metal canister with a single vacuum line attached to it. It also has an electrical connector.
Placement on the intake manifold: It is mounted on the top-rear side of the intake manifold, typically near the firewall.
Associated components: It is in close proximity to the throttle body, Idle Speed Control (ISC) valve, and other vacuum lines and sensors."

 

[AubieXX]

This is what I've found so far, but I have never actually seen one on a 3FE. Still not sure if this is a real thing or some sort of holdover from earlier models.
I got no hits after searching various VINs on partsouq for both FJ80s and FJ62s on "HAC" or "ALTITUDE" or "89464-35010" which is a part number that came up in a search.

"Diagram and location
Simplified diagram of the 3FE intake system
The HAC sensor is located on the intake manifold, next to the throttle body and other sensors. It is a vacuum-controlled sensor that works with the Engine Control Unit (ECU).
Specifics of the sensor's location
Sensor appearance: The HAC sensor is a small, round, or square metal canister with a single vacuum line attached to it. It also has an electrical connector.
Placement on the intake manifold: It is mounted on the top-rear side of the intake manifold, typically near the firewall.
Associated components: It is in close proximity to the throttle body, Idle Speed Control (ISC) valve, and other vacuum lines and sensors."

Thanks. I've been reading similar things. I have not been able to actually see what the stated "HAC sensor" looks like or where it is.

 

[jonheld]

Thanks. I've been reading similar things. I have not been able to actually see what the stated "HAC sensor" looks like or where it is.

I'm assuming your truck is a USDM vehicle.
I'd be willing to bet that it doesn't exist. 99.9% of the time, the FSM is spot on. However, several items/specifications found in various FSMs are holdovers from earlier years/different markets.
The fact that I can't identify an ECU pinout for the device, nor is there any mention of it in any document kind of points to that.

The issue now is to find out what the ECU is complaining about.

Have you checked all mechanical adjustments? Remember, 1st generation EFI from 1986.
To reset the ECU and clear codes, simply remove the 15 amp EFI fuse in the relay box on the left fender. It's less invasive than removing a battery terminal and accomplishes the same thing.