Unsolvable Engine Code 31
#1
Driver School Candidate
Thread Starter
Join Date: Mar 2022
Location: FL
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Unsolvable Engine Code 31
Hi, I have a 1993 LS400 which has recently had a lot of work done to it. In December, my dad and I replaced all the engine seals and gaskets as well as the starter and a bunch of other things. It ran fine but then started giving me engine code 31 which we traced to the MAF sensor. So we replaced it (from another 93 LS) and tested it, and it appears fine. I drove it back from their house to where I live, which is about 2.5 hours on the highway. It drove great - no more codes or issues. When I got it back, it still worked great, The next day I was going somewhere and all of a sudden I get a CEL. Checked later that day and its code 31, again. This time we assumed maybe the ECU. Last week we took it out and turns out it was replaced by the previous owner in 2018, which has a lifetime warranty. Just heard from the ECU manufacturer this morning that they see no issues with the ECU. Now I'm at a loss because I genuinely have no clue as to what would cause this anymore. Any help would be greatly appreciated.
A little more about the issues it's giving me - it only gives me the code when I'm not on the accelerator. When slowing down or foot off the gas, I get it but as soon as I start speeding up it goes away. It sometimes dies at idle, it often has an erratic idle, it sometimes has a high idle, and after driving about 30-45 minutes on normal streets it will do this weird thing where it jerks and bucks when at idle or when I am below 20 mph. It feels like something is about to explode. Since the CEL only comes on when I'm not accelerating, maybe it has something to do with air flow? Maybe AFM? Oxygen Sensors? I don't know anymore. I really love this car but it keeps giving problem after problem and I am out of ideas of what to fix next.
A little more about the issues it's giving me - it only gives me the code when I'm not on the accelerator. When slowing down or foot off the gas, I get it but as soon as I start speeding up it goes away. It sometimes dies at idle, it often has an erratic idle, it sometimes has a high idle, and after driving about 30-45 minutes on normal streets it will do this weird thing where it jerks and bucks when at idle or when I am below 20 mph. It feels like something is about to explode. Since the CEL only comes on when I'm not accelerating, maybe it has something to do with air flow? Maybe AFM? Oxygen Sensors? I don't know anymore. I really love this car but it keeps giving problem after problem and I am out of ideas of what to fix next.
#2
I believe your car has a Karman-Vortex type MAF. Do not spray any kind of cleaner into these type of sensors. Because you replaced the existing with a used unit, you can't know if the replacement unit is faulty as well.
You can try this to narrow down if it's the MAF or the electrical circuit for the MAF that's the issue: https://easyautodiagnostics.com/misc...-sensor-test-1
Yamae might chime in soon with some good advice.
You can try this to narrow down if it's the MAF or the electrical circuit for the MAF that's the issue: https://easyautodiagnostics.com/misc...-sensor-test-1
Yamae might chime in soon with some good advice.
#3
Moderator
It needs to use an oscilloscope to precisely diagnose the Karman Vortex air flow meter. Without it, it would not be easy to judge since you need to observe the oscillating waveform and measure the change of time interval of pulses. Is it possible for you to observe the waveform?
A simple checking method is to replace to a good working one. But it seems to me that you already have done it. Was the one you used a genuine one and confirmed good when it was used at another 93? It is the often case that many aftermarket ones are not fully compatible and many owners are not happy with those.
A simple checking method is to replace to a good working one. But it seems to me that you already have done it. Was the one you used a genuine one and confirmed good when it was used at another 93? It is the often case that many aftermarket ones are not fully compatible and many owners are not happy with those.
#4
Pole Position
Hi, I have a 1993 LS400 which has recently had a lot of work done to it. In December, my dad and I replaced all the engine seals and gaskets as well as the starter and a bunch of other things. It ran fine but then started giving me engine code 31 which we traced to the MAF sensor. So we replaced it (from another 93 LS) and tested it, and it appears fine. I drove it back from their house to where I live, which is about 2.5 hours on the highway. It drove great - no more codes or issues. When I got it back, it still worked great, The next day I was going somewhere and all of a sudden I get a CEL. Checked later that day and its code 31, again. This time we assumed maybe the ECU. Last week we took it out and turns out it was replaced by the previous owner in 2018, which has a lifetime warranty. Just heard from the ECU manufacturer this morning that they see no issues with the ECU. Now I'm at a loss because I genuinely have no clue as to what would cause this anymore. Any help would be greatly appreciated.
A little more about the issues it's giving me - it only gives me the code when I'm not on the accelerator. When slowing down or foot off the gas, I get it but as soon as I start speeding up it goes away. It sometimes dies at idle, it often has an erratic idle, it sometimes has a high idle, and after driving about 30-45 minutes on normal streets it will do this weird thing where it jerks and bucks when at idle or when I am below 20 mph. It feels like something is about to explode. Since the CEL only comes on when I'm not accelerating, maybe it has something to do with air flow? Maybe AFM? Oxygen Sensors? I don't know anymore. I really love this car but it keeps giving problem after problem and I am out of ideas of what to fix next.
A little more about the issues it's giving me - it only gives me the code when I'm not on the accelerator. When slowing down or foot off the gas, I get it but as soon as I start speeding up it goes away. It sometimes dies at idle, it often has an erratic idle, it sometimes has a high idle, and after driving about 30-45 minutes on normal streets it will do this weird thing where it jerks and bucks when at idle or when I am below 20 mph. It feels like something is about to explode. Since the CEL only comes on when I'm not accelerating, maybe it has something to do with air flow? Maybe AFM? Oxygen Sensors? I don't know anymore. I really love this car but it keeps giving problem after problem and I am out of ideas of what to fix next.
Thread
Thread Starter
Forum
Replies
Last Post
bdazzler
LS - 1st and 2nd Gen (1990-2000)
15
11-30-15 10:39 AM