Hi all, I have seen a lot of posts regarding this issue and very few solutions, so here goes my story / fix on my 1993 LC...
Note: This should apply to 1994 and earlier Toyota's with a VAF Meter (not a MAF Sensor).
Short Story:
Issue:
Hesitation / Stumbling whenever (could be cold, hot, city or hwy driving).
Did not kill the engine, just came down to idle for 20-30 seconds (sometimes less) and then started back up again like nothing every happened.
Occurred 1 / week at first, then over time occurred almost every trip.
No Codes, OBD1
Fix - connections inside VAF Meter.
The long - details:
Just over a year ago, I got my stock cruiser - ran great, slight stumble on my way home from purchase, but no biggie, it's 20+ years old - "that's normal, right"... Ran fine for a week or two, then over the next few months became more frequent. A few months later, it was daily, a few months later, it was nearly every trip - finally, I can start troubleshooting...
I checked a bunch of things, nothing worked. Downloaded the FSM (Thanks Mud!) and discovered there were 13+ associated systems contributing to hesitation Toyota wants you to diagnose - lol, what a joke. Internet searches turned up numerous forums/posts regarding the same thing, but no concrete solutions. Most posters were just never heard from again. Those who still had thier rigs said they just live with it (a year later). I figured the dealer would have some old timer around the shop, so I took it to camelback. They had it for a week, started by changing some fuel system related parts - no help. I took it back.
I decided I had to hunker down and dig deep to troubleshoot this, so I started a model based problem solving exercise and created an excel based punch list of every system to check. I covered nearly every sensor, input, and output to/from the ECU and monitored signals while wiggling wires and while driving. Since it was intermittent, I had to wait a day or so between results; so I hooked up 2 multi-meters simultaneously to cut troubleshooting time in half. I learned my truck intimately and replaced a few items that people suggested replacing on these forums when I was at my wits end and willing to try anything. Spent a solid 3-4 months troubleshooting this with my ECU hanging out everywhere I went, but finally found the culprit. Have 1000 miles on the odometer since the fix - yay!
Things dealer replaced:
Fuel pump relay
Fuel pump resistor
Things I checked:
Almost everything Fuel, Air, and Spark and Emissions related.
Things I replaced when I got a strong lead from somewhere:
Fuel Pump
ECT Temp sensor
Both Oxygen Sensors
Real Fix:
Connections internal to VAF Meter were loose coming from the VAF meter bulkhead connector, (between the VAF and the wire harness).
Toyota incorporated a design as follows:
Imagine a prong sticking out, hovering over a PCB. There's a 1/8" gap to close. One might think to just solder the prong to the PCB (printed circuit board) One would be wrong. Instead, devise a thin piece of thin metal in a "z" shape to bridge the gap between the prong and the circuit board. This metal is soldered onto the prong (coming from the VAF meter bulkhead connector, between the engine wiring harness connector) but just "touching" the PCB of the VAF (at least in my particular case). What appears to have occurred is the "touch point" has corroded from 20+ years of micro amounts of voltage arcing.
Once the problem was persistent enough and was able to narrow down this specific location, I was lucky to have someone who was easy on the eyes hold the engine at 2500 rpm. Then moving the harness to the VAF caused the stumbling.
Note: There was no stumbling effect at idle, which is why this same check produced no ill result 4 months prior when done without an assistant (talk about awesome - being right there before).
This solution was just to bend the prongs down a bit to improve this connection. The future backup solution is to solder the prongs to the PCB if it occurs again (so far 1000+ miles and stI'll running great).
keywords: volume air flow meter, mass air flow sensor, maf, afm, oxygen sensor, 02, o2
Note: This should apply to 1994 and earlier Toyota's with a VAF Meter (not a MAF Sensor).
Short Story:
Issue:
Hesitation / Stumbling whenever (could be cold, hot, city or hwy driving).
Did not kill the engine, just came down to idle for 20-30 seconds (sometimes less) and then started back up again like nothing every happened.
Occurred 1 / week at first, then over time occurred almost every trip.
No Codes, OBD1
Fix - connections inside VAF Meter.
The long - details:
Just over a year ago, I got my stock cruiser - ran great, slight stumble on my way home from purchase, but no biggie, it's 20+ years old - "that's normal, right"... Ran fine for a week or two, then over the next few months became more frequent. A few months later, it was daily, a few months later, it was nearly every trip - finally, I can start troubleshooting...
I checked a bunch of things, nothing worked. Downloaded the FSM (Thanks Mud!) and discovered there were 13+ associated systems contributing to hesitation Toyota wants you to diagnose - lol, what a joke. Internet searches turned up numerous forums/posts regarding the same thing, but no concrete solutions. Most posters were just never heard from again. Those who still had thier rigs said they just live with it (a year later). I figured the dealer would have some old timer around the shop, so I took it to camelback. They had it for a week, started by changing some fuel system related parts - no help. I took it back.
I decided I had to hunker down and dig deep to troubleshoot this, so I started a model based problem solving exercise and created an excel based punch list of every system to check. I covered nearly every sensor, input, and output to/from the ECU and monitored signals while wiggling wires and while driving. Since it was intermittent, I had to wait a day or so between results; so I hooked up 2 multi-meters simultaneously to cut troubleshooting time in half. I learned my truck intimately and replaced a few items that people suggested replacing on these forums when I was at my wits end and willing to try anything. Spent a solid 3-4 months troubleshooting this with my ECU hanging out everywhere I went, but finally found the culprit. Have 1000 miles on the odometer since the fix - yay!
Things dealer replaced:
Fuel pump relay
Fuel pump resistor
Things I checked:
Almost everything Fuel, Air, and Spark and Emissions related.
Things I replaced when I got a strong lead from somewhere:
Fuel Pump
ECT Temp sensor
Both Oxygen Sensors
Real Fix:
Connections internal to VAF Meter were loose coming from the VAF meter bulkhead connector, (between the VAF and the wire harness).
Toyota incorporated a design as follows:
Imagine a prong sticking out, hovering over a PCB. There's a 1/8" gap to close. One might think to just solder the prong to the PCB (printed circuit board) One would be wrong. Instead, devise a thin piece of thin metal in a "z" shape to bridge the gap between the prong and the circuit board. This metal is soldered onto the prong (coming from the VAF meter bulkhead connector, between the engine wiring harness connector) but just "touching" the PCB of the VAF (at least in my particular case). What appears to have occurred is the "touch point" has corroded from 20+ years of micro amounts of voltage arcing.
Once the problem was persistent enough and was able to narrow down this specific location, I was lucky to have someone who was easy on the eyes hold the engine at 2500 rpm. Then moving the harness to the VAF caused the stumbling.
Note: There was no stumbling effect at idle, which is why this same check produced no ill result 4 months prior when done without an assistant (talk about awesome - being right there before).
This solution was just to bend the prongs down a bit to improve this connection. The future backup solution is to solder the prongs to the PCB if it occurs again (so far 1000+ miles and stI'll running great).
keywords: volume air flow meter, mass air flow sensor, maf, afm, oxygen sensor, 02, o2
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