HELP! all i did was change valve cover gasket

[gorbilax]

You're going to pay through the nose for a new VAF. It's worth the effort to at least try to salvage what you have first. This may seem like a ridiculous suggestion, but I learned to solder when I was a kid by building kits like these from Velleman. You can practice and build confidence without risking destroying a hard to replace VAF... Looks like they still make them, and there's a whole series: https://www.amazon.com/Velleman-MK129-Crawling-Microbug/dp/B000TA58HQ

As far as the codes go, what are they? Have you followed the flow charts in the factory service manual (FSM) to see which one Mr. T says you should start troubleshooting first? Throwing parts at a problem often doesn't get to the root of the issue and just empties your wallet in the process.

 

[1994LC]

My codes are:

21- main oxygen sensor- problem in main oxygen sensor circuit- ecm or circuit

24- intake air temp- open or short in the intake air sensor temperature sensor or circuit- intake air temp circuit or ecm

31-airflow sensor- open or short in airflow circuit- airflow sensor or circuit or ecm

 

[tech_dog]

Based on those codes, ChatGPT says you should check the list below. I'm not a good enough mechanic to know if it's correct, but I've found the AI hints to be helpful. It's trained on the ih8mud forum and more.

Based on codes AND the fact that you just changed your HCG:

1. Inspect All Electrical Connections (Priority #1)​

Since they had to remove or move several sensors, a loose or disconnected connector is the most likely cause.

• Check the MAF/IAT sensor plug: Ensure it’s fully seated and no pins are bent or corroded.
• Check the MAP sensor connection: They might have bumped or stretched the wiring.
• Inspect oxygen sensor wiring: If any wires were tugged or pinched during reassembly, they could be damaged.

2. Look for Vacuum Leaks (Priority #2)​

• A disconnected or cracked vacuum hose, especially to the MAP sensor, could trigger the Code 31 (MAP sensor issue).
• Since they removed the valve cover, ensure all vacuum hoses are properly reconnected and routed.

3. Inspect the Air Intake System (Priority #3)​

• If the MAF/IAT sensor wasn’t plugged in or was damaged, it would trigger Code 24 (IAT sensor fault).
• Ensure the intake tubing is fully connected and clamped down—any leaks before the throttle body can cause bad sensor readings.

Based on codes only:

1. Check for Vacuum Leaks​

• Since the MAP sensor (Code 31) is crucial for air-fuel calculations, a vacuum leak can cause issues with its readings.
• Inspect all vacuum hoses around the intake manifold, throttle body, and MAP sensor.

2. Check the Intake Air Temperature (IAT) Sensor (Code 24)​

• The IAT sensor is part of the Mass Air Flow (MAF) sensor on some models, but on the FZJ80, it's usually integrated into the air intake system.
• Unplug the IAT sensor and check for corrosion on the connector.
• Test the resistance of the sensor using a multimeter—it should change with temperature.

3. Inspect the MAP Sensor (Code 31)​

• Make sure the vacuum hose to the MAP sensor is intact and properly connected.
• If possible, test the MAP sensor output voltage with a multimeter to see if it's responding correctly to vacuum changes.

4. Check the Oxygen Sensor (Code 21)​

• A bad O2 sensor can cause poor fuel mixture and rough running.
• If the engine is running rich or lean, the O2 sensor may not be giving correct feedback.
• Inspect the O2 sensor wiring and connectors for damage.
• If needed, test the O2 sensor voltage output with a multimeter or replace it if it’s old.

5. Check for Shared Wiring Issues​

• The IAT and MAP sensors may share wiring, so look for broken, frayed, or disconnected wires.
• If there was recent engine work, make sure all connectors are plugged in properly.

Are you disconnecting the battery between tests? You probably want to reset your ECU and clear codes.

 

[CharlieS]

Don't waste your time on GenAI. It doesn't know the difference between a MAF and a VFM, and that a 94 doesn't have a MAP sensor. Its day may come, but it isn't today.

 

[tech_dog]

Don't waste your time on GenAI. It doesn't know the difference between a MAF and a VFM, and that a 94 doesn't have a MAP sensor. Its day may come, but it isn't today.

AI consolidates what it reads and generally reflects the consensus. It will mimic what it reads, including incorrect terminology. When I have ChatGPT show sources, it often links to iH8mud posts, so it will embed "knowledge" that's both correct and incorrect.

Never blindly trust, but ChatGPT can give you the "jist" of a great deal of reading, and I've found it often helpful. Think of it as an avid reading teen who's kinda gullible.

( I developed AI for a while before I retired. This was a response to a deleted comment)

 

[BILT4ME]

AI consolidates what it reads and generally reflects the consensus. It will mimic what it reads, including incorrect terminology. When I have ChatGPT show sources, it often links to iH8mud posts, so it will embed "knowledge" that's both correct and incorrect.

Never blindly trust, but ChatGPT can give you the "jist" of a great deal of reading, and I've found it often helpful. Think of it as an avid reading teen who's kinda gullible.

( I developed AI for a while before I retired.)

Great, but don't muddy the waters with AI crap.

The FSM has a troubleshooting sequence and system that needs to be followed.

Don't follow AI horse hockey.

Do it correctly or pay for it ten times over.

 

[tech_dog]

This is a good use case for AI, correlating potential issues with codes and work just done. That's why I offered up the suggestions.

 

[Njck22]

Based on those codes, ChatGPT says you should check the list below. I'm not a good enough mechanic to know if it's correct, but I've found the AI hints to be helpful. It's trained on the ih8mud forum and more.

Based on codes AND the fact that you just changed your HCG:

1. Inspect All Electrical Connections (Priority #1)​

Since they had to remove or move several sensors, a loose or disconnected connector is the most likely cause.

• Check the MAF/IAT sensor plug: Ensure it’s fully seated and no pins are bent or corroded.
• Check the MAP sensor connection: They might have bumped or stretched the wiring.

No MAP Sensor on 1FZ

• Inspect oxygen sensor wiring: If any wires were tugged or pinched during reassembly, they could be damaged.

Oxygen sensor wiring would not have been disconnected during valve cover gasket job.

2. Look for Vacuum Leaks (Priority #2)​

• A disconnected or cracked vacuum hose, especially to the MAP sensor, could trigger the Code 31 (MAP sensor issue).

Again, no MAP sensor,

• Since they removed the valve cover, ensure all vacuum hoses are properly reconnected and routed.

3. Inspect the Air Intake System (Priority #3)​

• If the MAF/IAT sensor wasn’t plugged in or was damaged, it would trigger Code 24 (IAT sensor fault).
• Ensure the intake tubing is fully connected and clamped down—any leaks before the throttle body can cause bad sensor readings.

Based on codes only:

1. Check for Vacuum Leaks​

• Since the MAP sensor (Code 31) is crucial for air-fuel calculations, a vacuum leak can cause issues with its readings.
• Inspect all vacuum hoses around the intake manifold, throttle body, and MAP sensor.

2. Check the Intake Air Temperature (IAT) Sensor (Code 24)​

• The IAT sensor is part of the Mass Air Flow (MAF) sensor on some models, but on the FZJ80, it's usually integrated into the air intake system.
• Unplug the IAT sensor and check for corrosion on the connector.
• Test the resistance of the sensor using a multimeter—it should change with temperature.

3. Inspect the MAP Sensor (Code 31)​

• Make sure the vacuum hose to the MAP sensor is intact and properly connected.
• If possible, test the MAP sensor output voltage with a multimeter to see if it's responding correctly to vacuum changes.

4. Check the Oxygen Sensor (Code 21)​

• A bad O2 sensor can cause poor fuel mixture and rough running.
• If the engine is running rich or lean, the O2 sensor may not be giving correct feedback.
• Inspect the O2 sensor wiring and connectors for damage.
• If needed, test the O2 sensor voltage output with a multimeter or replace it if it’s old.

5. Check for Shared Wiring Issues​

• The IAT and MAP sensors may share wiring, so look for broken, frayed, or disconnected wires.
• If there was recent engine work, make sure all connectors are plugged in properly.

Are you disconnecting the battery between tests? You probably want to reset your ECU and clear codes.

I 100% see the value of AI LLMs. But forums are a place their responses do not belong. Generic, broad, responses from a non-specific LLM trained to make responses that "sound" good is not helpful in a forum setting. The point of a forum is to have quality content that is not aggregate and is specific and relevant. If MUD was full of AI responses, how would valuable information be distinguished? Then we will train future models on that same inaccurate information? Same reason people add "reddit" to the end of general queries when googling. They want information that has been curated by a human to be relevant. This is a problem across the internet currently. Be a part of the solution, At least review what information they spit out.

 

[BILT4ME]

This is a good use case for AI, correlating potential issues with codes and work just done. That's why I offered up the suggestions.

And you have just generated more poor source code for actual real information within the Mud forum.

Garbage in, garbage out.