Car stalling when tapping on MAF and TPS
05-19-18, 07:00 PM
#1
Driver School Candidate
Thread Starter
car runs great when cold. Once warm accelerates like a slug.
UPDATE: no more stalling. MAF was replaced which cured that.
But Does anyone know when the TPS actually comes into play? Always? Only open loop?
Little background, just bought this car (1993 ls400) with some issues. Been working on fixing it up. When I first bought it it ran like absolute ****. Turned out to be bad ECU. Replaced ecu and it runs wayyy better but have some different issues now.
After replacing ECU car ran flawless when cold. As soon as it got to operating temp it would stall out randomly. Then would fire right back up run for a few minutes and stall out again. Ended up throwing a MAF code. Tested bad, replaced and it quit stalling. Now we’re here
Car still runs flawless when cold. Full of power. Once the idle drops down to 550-600 (idles perfect) when warmed up has bad throttle response at low rpms. Really slow off the line. Once you hit like 3500 rpms the power will hit again. With MAF unplugged it isles worse but excelerates better.
Another strange thing is once once put into gear idle drops down to 300-400 rpms.
i need ideas.
But Does anyone know when the TPS actually comes into play? Always? Only open loop?
Little background, just bought this car (1993 ls400) with some issues. Been working on fixing it up. When I first bought it it ran like absolute ****. Turned out to be bad ECU. Replaced ecu and it runs wayyy better but have some different issues now.
After replacing ECU car ran flawless when cold. As soon as it got to operating temp it would stall out randomly. Then would fire right back up run for a few minutes and stall out again. Ended up throwing a MAF code. Tested bad, replaced and it quit stalling. Now we’re here
Car still runs flawless when cold. Full of power. Once the idle drops down to 550-600 (idles perfect) when warmed up has bad throttle response at low rpms. Really slow off the line. Once you hit like 3500 rpms the power will hit again. With MAF unplugged it isles worse but excelerates better.
Another strange thing is once once put into gear idle drops down to 300-400 rpms.
i need ideas.
Last edited by shagool22; 05-31-18 at 09:43 PM.
05-22-18, 05:54 AM
#2
Have you cleaned the connectors with electronics cleaner? Could be, over time you've got some dirt build up or looseness in the connections that when you tap it, cause a break in the communication and cause the engine to die.
05-22-18, 07:26 AM
#3
Driver School Candidate
Thread Starter
That did indeed work for the TPS. No more code for that and tapping on it doesn’t make car stall anymore. And I’m 90% sure the MAF is definitely bad. Unplugging it has no change in car performance. Actually might run a little better without it. Got a new one on the way. Hopefully that takes care of the issue! Thanks!
05-22-18, 08:45 AM
#4
Pole Position
If it's bad, which it does sound like it is, it will run better when unplugged. Don't drive too long with it unplugged or other parts will go bad. Usually when AFM is bad it's the Intake Air Temp sensor inside the AFM. That doesn't always throw a code. Seeing how you have a new AFM coming, let us know the results when you put it on. And remember, DO NOT clean the AFM with any cleaner or you will ruin that one also.
05-22-18, 11:39 AM
#5
Driver School Candidate
Thread Starter
The "MAF" is actually "AFM" on your 93.
If it's bad, which it does sound like it is, it will run better when unplugged. Don't drive too long with it unplugged or other parts will go bad. Usually when AFM is bad it's the Intake Air Temp sensor inside the AFM. That doesn't always throw a code. Seeing how you have a new AFM coming, let us know the results when you put it on. And remember, DO NOT clean the AFM with any cleaner or you will ruin that one also.
If it's bad, which it does sound like it is, it will run better when unplugged. Don't drive too long with it unplugged or other parts will go bad. Usually when AFM is bad it's the Intake Air Temp sensor inside the AFM. That doesn't always throw a code. Seeing how you have a new AFM coming, let us know the results when you put it on. And remember, DO NOT clean the AFM with any cleaner or you will ruin that one also.
I’ve heard MAF and AFM.. i always though an air flow meter has a flapper door. And a MAF does not.
But it’s not getting driven at all. It’s actually a donor car for the motor swap. Just wanna get it running like a top before I pull it. And yes I think previous owner killed the maf/AFM. He tried cleaning it when the problem was a bad ecu.. ecu has been replaced with a known good refurbished one.
and yes I will let you know if the new MAF/AFM cures the problem. Should be here by Friday. Thanks for the inputs!
05-23-18, 08:16 PM
#7
I’ve heard MAF and AFM.. i always though an air flow meter has a flapper door. And a MAF does not.
But it’s not getting driven at all. It’s actually a donor car for the motor swap. Just wanna get it running like a top before I pull it. And yes I think previous owner killed the maf/AFM. He tried cleaning it when the problem was a bad ecu.. ecu has been replaced with a known good refurbished one.
and yes I will let you know if the new MAF/AFM cures the problem. Should be here by Friday. Thanks for the inputs!
and yes I will let you know if the new MAF/AFM cures the problem. Should be here by Friday. Thanks for the inputs!
AFM is usually air flow meter (directly measures the volumetric flow rate, or just "flow rate," or just "flow," and needs further corrections to get a mass flow signal)
your engine's fuel injection controller cares about the mass of the air going in, not the volumetric flow rate. The difference between the two will change with air density (altitude and temperature, primarily).
The MAF is typically a hot-wire anemometer that measures mass flow pretty much directly. A hot wire or film has a control circuit around it to maintain it at a constant temperature, and the current needed to do that indicates the mass flow. Yes, the fluid and heat transfer physics mean the signal is proportional to the fluid density times the fluid flow rate (proportional to mass flow), rather than simply volumetric flow rate.
Many AFMs do use a barn door flapper and then a potentiometer to measure the angle, which is calibrated to give the volumetric flow rate, which can then be corrected using a temperature sensor (to account for varying density) to give mass flow.
This Lexus has a less common type of AFM that is based on a Karman vortex counter. It has a vortex inducer in the air flow, then an optical sensor that can detect each time a vortex goes past it. Due to the physics of the flow, the frequency of this Karman vortex street (a sequence of vortices) is proportional to the _velocity_ of the fluid. So in this case, to figure out the mass flow, there is also a temperature sensor in there to estimate the density and multiply by the velocity to get a mass flow estimate for the fuel injection controller.
So the Lexus one _is_ an AFM since it measures velocity directly rather than mass flow directly, but it is not a flapper like most AFMs.
So if you're going to be replacing it anyway, you might take the existing one apart. Might be interesting. If there is a temp sensor bad, that might be an easy fix. Another thing that could be bad is a reflective mirror surface that the optical sensor uses - if that is no longer reflective, that would be a problem. And of course if the optical sensor is covered in gunk, that might clean up easily. It should be more robust than a hot-wire would be.
And BTW, it sounds like you are doing a great job on the debugging so far.
Last edited by oldskewel; 05-24-18 at 04:11 PM.
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shagool22 (05-26-18)
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05-25-18, 09:36 AM
#8
Oldskewel- Great explain on the different between the MAF & AFM. So the 1st gen up to 94 is equipped w/ AFM then MAF for 95 & up?
Legender- Can you elaborate on why can't the AFM be cleaned w/ MAF cleaner? Thanks
Legender- Can you elaborate on why can't the AFM be cleaned w/ MAF cleaner? Thanks
05-26-18, 06:36 PM
#9
Driver School Candidate
Thread Starter
MAF is usually m*** air flow sensor (measures the mass flow rate pretty directly)
AFM is usually air flow meter (directly measures the volumetric flow rate, or just "flow rate," or just "flow," and needs further corrections to get a mass flow signal)
your engine's fuel injection controller cares about the mass of the air going in, not the volumetric flow rate. The difference between the two will change with air density (altitude and temperature, primarily).
The MAF is typically a hot-wire anemometer that measures mass flow pretty much directly. A hot wire or film has a control circuit around it to maintain it at a constant temperature, and the current needed to do that indicates the mass flow. Yes, the fluid and heat transfer physics mean the signal is proportional to the fluid density times the fluid flow rate (proportional to mass flow), rather than simply volumetric flow rate.
Many AFMs do use a barn door flapper and then a potentiometer to measure the angle, which is calibrated to give the volumetric flow rate, which can then be corrected using a temperature sensor (to account for varying density) to give mass flow.
This Lexus has a less common type of AFM that is based on a Karman vortex counter. It has a vortex inducer in the air flow, then an optical sensor that can detect each time a vortex goes past it. Due to the physics of the flow, the frequency of this Karman vortex street (a sequence of vortices) is proportional to the _velocity_ of the fluid. So in this case, to figure out the mass flow, there is also a temperature sensor in there to estimate the density and multiply by the velocity to get a mass flow estimate for the fuel injection controller.
So the Lexus one _is_ an AFM since it measures velocity directly rather than mass flow directly, but it is not a flapper like most AFMs.
So if you're going to be replacing it anyway, you might take the existing one apart. Might be interesting. If there is a temp sensor bad, that might be an easy fix. Another thing that could be bad is a reflective mirror surface that the optical sensor uses - if that is no longer reflective, that would be a problem. And of course if the optical sensor is covered in gunk, that might clean up easily. It should be more robust than a hot-wire would be.
And BTW, it sounds like you are doing a great job on the debugging so far.
AFM is usually air flow meter (directly measures the volumetric flow rate, or just "flow rate," or just "flow," and needs further corrections to get a mass flow signal)
your engine's fuel injection controller cares about the mass of the air going in, not the volumetric flow rate. The difference between the two will change with air density (altitude and temperature, primarily).
The MAF is typically a hot-wire anemometer that measures mass flow pretty much directly. A hot wire or film has a control circuit around it to maintain it at a constant temperature, and the current needed to do that indicates the mass flow. Yes, the fluid and heat transfer physics mean the signal is proportional to the fluid density times the fluid flow rate (proportional to mass flow), rather than simply volumetric flow rate.
Many AFMs do use a barn door flapper and then a potentiometer to measure the angle, which is calibrated to give the volumetric flow rate, which can then be corrected using a temperature sensor (to account for varying density) to give mass flow.
This Lexus has a less common type of AFM that is based on a Karman vortex counter. It has a vortex inducer in the air flow, then an optical sensor that can detect each time a vortex goes past it. Due to the physics of the flow, the frequency of this Karman vortex street (a sequence of vortices) is proportional to the _velocity_ of the fluid. So in this case, to figure out the mass flow, there is also a temperature sensor in there to estimate the density and multiply by the velocity to get a mass flow estimate for the fuel injection controller.
So the Lexus one _is_ an AFM since it measures velocity directly rather than mass flow directly, but it is not a flapper like most AFMs.
So if you're going to be replacing it anyway, you might take the existing one apart. Might be interesting. If there is a temp sensor bad, that might be an easy fix. Another thing that could be bad is a reflective mirror surface that the optical sensor uses - if that is no longer reflective, that would be a problem. And of course if the optical sensor is covered in gunk, that might clean up easily. It should be more robust than a hot-wire would be.
And BTW, it sounds like you are doing a great job on the debugging so far.
05-26-18, 06:43 PM
#10
Driver School Candidate
Thread Starter
Okay quick update. I got the new MAF installed and it fixed the stalling issue. And no more stalling when tapping on it or anything else. No CEL or codes.
On to the next issue; throttle response.
Giving it low steady throttle or wide open throttle it will spit and spudder until about 3k rpms and then will rev great. Before messing with TPS I decided to jump terminals fp and b+ in the diag box and these issues go away. Wide open throttle is flawless as well as low steady throttle.. also without terminals jumped when put into gear rpms will drop to 300ish. With terminals jumped this doesn’t happen. Thoughts?
Edit: this issue was there before new MAF. thought maybe it was because of the bad one
On to the next issue; throttle response.
Giving it low steady throttle or wide open throttle it will spit and spudder until about 3k rpms and then will rev great. Before messing with TPS I decided to jump terminals fp and b+ in the diag box and these issues go away. Wide open throttle is flawless as well as low steady throttle.. also without terminals jumped when put into gear rpms will drop to 300ish. With terminals jumped this doesn’t happen. Thoughts?
Edit: this issue was there before new MAF. thought maybe it was because of the bad one
Last edited by shagool22; 05-26-18 at 06:47 PM.
05-26-18, 11:32 PM
#11
Regarding the jumpering at the diagnosis box, I once took a more careful look at the circuit to see what it was really doing. It might help to understand what's going on. Here's my post on that from a while ago:
https://www.clublexus.com/forums/ls-...ml#post9777959
And glad to hear the new AFM fixed it. Once you're 100% sure (maybe already are) the old one is bad, you might want to take it apart to see what is bad. It might be something visually obvious.
https://www.clublexus.com/forums/ls-...ml#post9777959
And glad to hear the new AFM fixed it. Once you're 100% sure (maybe already are) the old one is bad, you might want to take it apart to see what is bad. It might be something visually obvious.
05-27-18, 09:53 AM
#12
Driver School Candidate
Thread Starter
So I believe when that was a coincidence yesterday. As shortly after I posted it ran out of gas lol. Didn’t realize it was that low. Now with gas jumpering the diag box has no effect.
Back to to my original post, the issue only happens at operating temp. When the car is completely cold it runs 100% power and throttle response. No lag, no hesitation, runs absolutely perfect. Then once it warms up it has bad throttle response at steady low rpm and WOT. Which causes a huge power loss. Until you hit 3k rpm then all power and throttle response comes back. Still no codes. Still idles well, although it seems to drop a little low.
Thanks for for all the input. I did find your comment on that link when I was doing some research.
Back to to my original post, the issue only happens at operating temp. When the car is completely cold it runs 100% power and throttle response. No lag, no hesitation, runs absolutely perfect. Then once it warms up it has bad throttle response at steady low rpm and WOT. Which causes a huge power loss. Until you hit 3k rpm then all power and throttle response comes back. Still no codes. Still idles well, although it seems to drop a little low.
Thanks for for all the input. I did find your comment on that link when I was doing some research.
05-27-18, 11:07 AM
#13
Tough problem to diagnose. I went through all kinds of tests when I had a similar problem a couple of years ago. That circuit I posted, with the analysis and tests mainly served to prevent me from buying unnecessary replacement parts (e.g., the resistor, relays). In the end I just had ruled out just about everything else and replaced the fuel pump, which was the right answer. Symptoms of a soft-failing fuel pump like I had are difficult.
In particular with your symptoms, the heat-related correlation is how a weak old fuel pump might behave. If you've run out of other things to consider, I'd go with a new fuel pump. Fuel filter too would be good. When I looked, a genuine Lexus pump was over $300, china brand ebay for $30, and the one I went with was an Amazon Denso for $100 that was actually made in Japan. I think a genuine fuel filter will be ~$40. Fuel filters can last forever or not - it all depends on the quality of gas you use over the lifetime of the car.
In particular with your symptoms, the heat-related correlation is how a weak old fuel pump might behave. If you've run out of other things to consider, I'd go with a new fuel pump. Fuel filter too would be good. When I looked, a genuine Lexus pump was over $300, china brand ebay for $30, and the one I went with was an Amazon Denso for $100 that was actually made in Japan. I think a genuine fuel filter will be ~$40. Fuel filters can last forever or not - it all depends on the quality of gas you use over the lifetime of the car.
05-27-18, 01:05 PM
#14
Driver School Candidate
Thread Starter
I thought the same about fuel pump. I did the fuel filter last week.
doing some more testing I took it for a drive and it was having it’s issues. Pulled over unplugged MAF, all power restored runs perfect with great power. Plug MAF back in drive it again lose all power and turns into a slug under 3k rpms. I always try to keep in mind that new parts aren’t always good parts. But 2 different MAFS both bad? Or could this be a wiring issue or something else? With MAF unplugged it does idle worse than with it plugged in.
doing some more testing I took it for a drive and it was having it’s issues. Pulled over unplugged MAF, all power restored runs perfect with great power. Plug MAF back in drive it again lose all power and turns into a slug under 3k rpms. I always try to keep in mind that new parts aren’t always good parts. But 2 different MAFS both bad? Or could this be a wiring issue or something else? With MAF unplugged it does idle worse than with it plugged in.
05-28-18, 10:14 PM
#15
Driver School Candidate
Thread Starter
New possible theory.. heat soak. As mentioned in my original post previous owner was only running factory backup electric fans. There was no hydraulic fan or shroud when I got the car. It’s still this way I wasn’t worried about it as I’m not going to be driving it and the car doesn’t over heat.
But could it be getting too hot and causing faulty IAT reading? Maybe a long shot but I’m not sure what to look for next.. Need some input here! Am I way over thinking things? Lol
But could it be getting too hot and causing faulty IAT reading? Maybe a long shot but I’m not sure what to look for next.. Need some input here! Am I way over thinking things? Lol