1991 Lexus LS400 Starts but dies, then won't start

[jp6296873]

Hello everyone. I bought a 1991 Lexus LS400 with 223k miles. I drove it home just fine yesterday, and started it a few times to hear the engine run. Today I drove to the parts store, and it started just fine. As I'm trying to leave, the car starts but then dies. The car will start momentarily, but immediately die, then I try to start it again but the only sound made is by the starter motor. Could someone inform me please as to what could be happening?

[Jeremy M.]

My first guess would be the crankshaft position sensor may be going out. To confirm this, check spark at any cylinder. If no spark is present, check spark coming from ignition coil. If no spark is present, check input to ignition coil (hook up test light to both wires feeding coil). If there is no pulse, confirm there is no security light or sensors unplugged. If all that is good, I'd replace the crankshaft sensor as the most likely culprit.

[jp6296873]

15 minutes ago, Jeremy M. said:

My first guess would be the crankshaft position sensor may be going out. To confirm this, check spark at any cylinder. If no spark is present, check spark coming from ignition coil. If no spark is present, check input to ignition coil (hook up test light to both wires feeding coil). If there is no pulse, confirm there is no security light or sensors unplugged. If all that is good, I'd replace the crankshaft sensor as the most likely culprit.

I will look into that, thank you. I'm hearing that it could be a fuel issue as well. I stepped on the pedal while starting it and I revved it to 3k rpm, but it would still die.

[Jeremy M.]

Ah. Yeah, with it being able to rev, you should still have spark, so CPS is less likely. Checking fuel pressure definitely wouldn't be a bad idea. If it's low, I'd recommend finding out if your car has an external fuel pump, and if so, replacing it and re-checking the pressure.

[RX400h06]

That’s a classic LS400 mystery, Julio—and you’re not alone. A few common culprits could be behind this “starts then dies” behavior:

1. Fuel Pump or Circuit Opening Relay

The fuel pump might be running only during cranking but not after. This often points to a faulty circuit opening relay or fuel pump ECU. Some owners have had success temporarily jumping the B+ and FP terminals in the diagnostic box under the hood to keep the pump running and confirm the issue.

2. MAF Sensor (Mass Air Flow)

A bad or disconnected MAF sensor can cause the engine to start and immediately stall. If the MAF is unplugged or faulty, the ECU may not deliver the correct fuel-air mix.

3. Immobilizer or ECU Issue

If the car had an ECU swap or immobilizer mismatch (especially between California and federal models), it might start briefly using the cold start injector, then shut off due to lack of injector pulse.

4. Igniter or No Injector Pulse

The ECU needs to see ignition signals from the igniter to keep firing the injectors. If the igniter is bad or not sending feedback, the ECU may cut fuel after startup.

5. Vacuum Leaks or Fuel Pressure Regulator

A large vacuum leak or failed fuel pressure regulator could cause the engine to stumble and die right after starting.

If you’re up for a quick test, try spraying a little carb cleaner into the intake while cranking. If it runs longer, you’re likely dealing with a fuel delivery issue.

[jp6296873]

4 hours ago, RX400h06 said:

 

That’s a classic LS400 mystery, Julio—and you’re not alone. A few common culprits could be behind this “starts then dies” behavior:

1. Fuel Pump or Circuit Opening Relay

The fuel pump might be running only during cranking but not after. This often points to a faulty circuit opening relay or fuel pump ECU. Some owners have had success temporarily jumping the B+ and FP terminals in the diagnostic box under the hood to keep the pump running and confirm the issue.

2. MAF Sensor (Mass Air Flow)

A bad or disconnected MAF sensor can cause the engine to start and immediately stall. If the MAF is unplugged or faulty, the ECU may not deliver the correct fuel-air mix.

3. Immobilizer or ECU Issue

If the car had an ECU swap or immobilizer mismatch (especially between California and federal models), it might start briefly using the cold start injector, then shut off due to lack of injector pulse.

4. Igniter or No Injector Pulse

The ECU needs to see ignition signals from the igniter to keep firing the injectors. If the igniter is bad or not sending feedback, the ECU may cut fuel after startup.

5. Vacuum Leaks or Fuel Pressure Regulator

A large vacuum leak or failed fuel pressure regulator could cause the engine to stumble and die right after starting.

If you’re up for a quick test, try spraying a little carb cleaner into the intake while cranking. If it runs longer, you’re likely dealing with a fuel delivery issue.

 

We managed to get it home, only by constantly mashing the gas pedal. We also had to hold the shift lock override button to get it in gear. It runs smooth otherwise until it's left to idle, then it dies. I asked my neighborhood mechanic and tells me it couls be the idle air control valve that needs cleaning or replacing. 

[RX400h06]

Did you call the previous owner to ask if he experienced the issue, previously? If you are not an experienced auto troubleshooter, I would recommend taking the car to shop that specializes in no start or stall issues. My son had a battery drain issue, so he took it to a local shop that is well known for troubleshooting difficult-to-resolve issues. The culprit turned out to be the alarm system - something they have dealt with and resolved in the past.

 

[jp6296873]

On 6/28/2025 at 2:59 PM, RX400h06 said:

 

Did you call the previous owner to ask if he experienced the issue, previously? If you are not an experienced auto troubleshooter, I would recommend taking the car to shop that specializes in no start or stall issues. My son had a battery drain issue, so he took it to a local shop that is well known for troubleshooting difficult-to-resolve issues. The culprit turned out to be the alarm system - something they have dealt with and resolved in the past.

 

 

 

On 6/27/2025 at 3:36 PM, Jeremy M. said:

Ah. Yeah, with it being able to rev, you should still have spark, so CPS is less likely. Checking fuel pressure definitely wouldn't be a bad idea. If it's low, I'd recommend finding out if your car has an external fuel pump, and if so, replacing it and re-checking the pressure.

I contacted the previous owner asking if he's had this issue. He said he's dealt with the same issue sometimes. All he told me was "There's a cable with a spring under a cover near the passenger firewall". I remember before the issue started, I removed the cruise control cover and a spring suddenly came out. I wasn't sure where the spring belonged so I put it away. A little bit after that is when the issue started. Not sure if I somehow messed with some kind of idle/throttle cable spring and that's why the car won't idle. Here's a picture of the spring that came out when I had removed the cover for the cruise control.

 

[Jeremy M.]

That spring certainly isn't from the factory. Does the owner have any information about where the spring was installed? Also, what cover are you referring to as the "cruise control cover"? Would you be able to take a photo of it?

[jp6296873]

21 hours ago, Jeremy M. said:

That spring certainly isn't from the factory. Does the owner have any information about where the spring was installed? Also, what cover are you referring to as the "cruise control cover"? Would you be able to take a photo of it?

It seems that the problem has been solved. I told my neighbor about what the previous owner had told me. It seems theprevious owner had this spring hooked onto the cable that goes from the throttle body to cruise control actuator, which apparently has a part in controlling the car's idle. When the spring fell out, the cable had nothing pulling on it, which is why the car wouldn't idle. Here is a picture of how it's been left.

Now I need to find out why I can't get the shifter to move, unless I press the shift lock override button. Thank you for the help.

 

[Jeremy M.]

As far as your shifter- do your brake lights work? If the car doesn't think the brakes are applied, it won't allow the shifter to leave park. Could be a bad brake switch, broken wire, or a faulty solenoid in your shifter assembly.

[jp6296873]

3 hours ago, Jeremy M. said:

As far as your shifter- do your brake lights work? If the car doesn't think the brakes are applied, it won't allow the shifter to leave park. Could be a bad brake switch, broken wire, or a faulty solenoid in your shifter assembly.

Brake lights are working properly. Now that you mention broken wires, the wiring harness in the trunk hinge seems to have two broken wires that the previous owner didn't fix. I suspect that those two broken wires are related to the shifter not moving without the shift lock override. My reverse lights also don't come on, and the reverse light in the dash comes on when I turn my headlights on, causing the car to downshift. I imagine those trunk hinge wires are the culprit. I'll see about fixing those wires and report back.