Car Hesitation

[scotty2hottyoki]

I have a 93 ls400 and i just recently replaced my faulty ecu and mass airflow sensor with good used parts. After I got my car out of the shop, i was driving right down the street and as i accelerated a little fast, the car started to hesitate and stutter. So i brought it straight back to the garage and had a mechanic check it out. So he test drove it and realized that if you accelerated slowly it wont hesistate, but if you step on it a little bit...as soon as it reaches around 2000 rpms it automatically starts to hesitate. So he suggested that i buy a throttle position sensor, so i bought one and had it replaced...but it the car is STILL acting up. Anybody out there have ANY suggestions of what it could be? Thanks

[dee2000]

I have a 93 ls400 and i just recently replaced my faulty ecu and mass airflow sensor with good used parts. After I got my car out of the shop, i was driving right down the street and as i accelerated a little fast, the car started to hesitate and stutter. So i brought it straight back to the garage and had a mechanic check it out. So he test drove it and realized that if you accelerated slowly it wont hesistate, but if you step on it a little bit...as soon as it reaches around 2000 rpms it automatically starts to hesitate. So he suggested that i buy a throttle position sensor, so i bought one and had it replaced...but it the car is STILL acting up. Anybody out there have ANY suggestions of what it could be? Thanks

Hi, I have 94, and it has the same problem. Just replaced the TPS but it does not help. Did you find out what happen to your situation? Thanks,

[scotty2hottyoki]

I have a 93 ls400 and i just recently replaced my faulty ecu and mass airflow sensor with good used parts. After I got my car out of the shop, i was driving right down the street and as i accelerated a little fast, the car started to hesitate and stutter. So i brought it straight back to the garage and had a mechanic check it out. So he test drove it and realized that if you accelerated slowly it wont hesistate, but if you step on it a little bit...as soon as it reaches around 2000 rpms it automatically starts to hesitate. So he suggested that i buy a throttle position sensor, so i bought one and had it replaced...but it the car is STILL acting up. Anybody out there have ANY suggestions of what it could be? Thanks

Hi, I have 94, and it has the same problem. Just replaced the TPS but it does not help. Did you find out what happen to your situation? Thanks,

The mechanic that I brought my car to recommended me to take my car to a lexus dealership and have them look at it...so i made an appointment and will find out on tuesday what the problem is.

[nc211]

you're not getting enough of one of the following three things:

1. fuel

2. air

3. spark

I assume your check engine light is not on? I ask, becuase if it were, your mechanic would of pulled the code. Actually, ask him if he checked the codes anyway, and post up what he said. My guess...in all honesty... you're fuel filter sounds like it is in need of replacement. It sounds like if you accelerate normally, the pump is capable of supplying enough fuel at the right pace. But when you ask for more fuel at a faster pace, it's getting locked up at the filter. This is pretty common, and if you check out www.lexls.com, you'll see the tutorial on the process. Not hard, a bit messy though. Highly recommend doing it on an empty tank if possible. OR, you can try a concentrated can of Seafoam on a 1/2 tank, and run the car pretty hard. If you haven't done that yet in general, I suggest a can of it just to clear out any possible water in the tank, and possibly clean up a fouled injector.

If not the fuel filter, then maybe it's in your air supply, and since you have a new tps, I think it might be time for the throttle body to be cleaned. But, you would also have a rough idle if that were the case. Question: Do you have a raw gas smell? I ask because if it is the air supply, and your intake is good, your cats maybe clogged. This will usually produce a strong raw gas smell, and after you run the car a bit, if you look under it, they will be glowing hot. Blake918 took his out one day and ran the religion out of it, which dislodged whatever was blocking the cat. I WOULD ASK HIM FIRST if you decide to try that. Don't do it without asking him first!

Next is the spark: you could have a fouled plug or bad wire. However, I would of thought the mechanic would of caught that right from the start. However, I don't know your mechanic, and unfortunetly there are those horror stories out there of buying more than you really needed. Not making accusations, just a thought.

Either way, you're engine isn't getting enough of one of those three things. I'm putting my money on the fuel supply.

[TexasLexus94]

I'm betting a bad wire or plug. Just before I brought my LS to a reputable repair shop for a smog test recently (you remember the story, NC211), I developed a really bad miss when accelerating. I was very frustrated, since I had the smog problem as well, and didn't need another problem. So I took all the plastic covers off the front of the engine, and lo and behold, found the longest new plug wire on one side had been restricted on reinstallation of the covers by some dope (TexLex). I replaced the new wire with an old wire I had saved, and the problem was solved. RLT. Runs like a top.

Hope your problem is as simple as mine, Scotty, since I fear that most repair shops will take you to the cleaners. Best of luck.

[LScott400]

Are your coils original?

[scotty2hottyoki]

you're not getting enough of one of the following three things:

1. fuel

2. air

3. spark

I assume your check engine light is not on? I ask, becuase if it were, your mechanic would of pulled the code. Actually, ask him if he checked the codes anyway, and post up what he said. My guess...in all honesty... you're fuel filter sounds like it is in need of replacement. It sounds like if you accelerate normally, the pump is capable of supplying enough fuel at the right pace. But when you ask for more fuel at a faster pace, it's getting locked up at the filter. This is pretty common, and if you check out www.lexls.com, you'll see the tutorial on the process. Not hard, a bit messy though. Highly recommend doing it on an empty tank if possible. OR, you can try a concentrated can of Seafoam on a 1/2 tank, and run the car pretty hard. If you haven't done that yet in general, I suggest a can of it just to clear out any possible water in the tank, and possibly clean up a fouled injector.

If not the fuel filter, then maybe it's in your air supply, and since you have a new tps, I think it might be time for the throttle body to be cleaned. But, you would also have a rough idle if that were the case. Question: Do you have a raw gas smell? I ask because if it is the air supply, and your intake is good, your cats maybe clogged. This will usually produce a strong raw gas smell, and after you run the car a bit, if you look under it, they will be glowing hot. Blake918 took his out one day and ran the religion out of it, which dislodged whatever was blocking the cat. I WOULD ASK HIM FIRST if you decide to try that. Don't do it without asking him first!

Next is the spark: you could have a fouled plug or bad wire. However, I would of thought the mechanic would of caught that right from the start. However, I don't know your mechanic, and unfortunetly there are those horror stories out there of buying more than you really needed. Not making accusations, just a thought.

Either way, you're engine isn't getting enough of one of those three things. I'm putting my money on the fuel supply.

My check light is not on. when my car was at the shop: the fuel filter, air filter, spark plugs, crank sensor, and mass airflow sensor were replaced...or so they say...i havent checked my car to confirm it yet...but i'm pretty sure they changed them out. my car is not idling rough and the shop check the cat for blockage, which there wasnt. i havent replaced the spark plugs wire, distributor caps or rotors.

Are your coils original?

im pretty sure the ignition coils are original. how can i determine if they are bad?

[93ls400walt]

I have a 93ls with the same issue. The rpm drops 5-8 hundred rpm. It feels as if the car slips into neutral, no forward acceleration. Sometimes the rpm will go up and down a few hundred rpm in a jerking fashion if I hold the pedal steady where it was when this starts. If I let off the accelerater then re-apply the gas slower there is no problem. It is worse if there is a load on the car, such as, the A/C is on or I have a couple of passengers.

I have a code 41 for which I have replaced the TPS and adjusted it many times. The code does not go away. Cleaned the throttle body several times, also the ERG valve, ran many cans of Seafoam and BG44K, Replaced the in-tank fuel screen, the underbody fuel filter, the plugs,wires,caps,rotorsand coils. This all did help with better acceleration, but did not fix the problem.

I have been leaning toward the ECM as it will throw a code 41 also as well as the wire harness to the TPS will code 41. I also read that the fuel pump is a two stage unit. It has a normal pressure and a higher one for more aggressive acceleration. Anyone else heard of this? It was in a British car mag for LS400 diagnostics.

I am interested to hear what was going on with your ls that prompted you to replace the ECM and the Mass air flow unit. And did your car do this before the change? If not I would put the old ECM back in and see if it still does it.

If you go with the dealer please post their findings. There has not been any post except yours that matches my specific problem.

Good luck, Walt

[LScott400]

im pretty sure the ignition coils are original. how can i determine if they are bad?

See pages 6 & 7.

onvehicleinspection.pdf

Here is a Link that explains coils and makes the point that a basic resistance test may test good while the coil may start to fail under load. I mention this because that was the case with our '94.

[scotty2hottyoki]

I have a 93ls with the same issue. The rpm drops 5-8 hundred rpm. It feels as if the car slips into neutral, no forward acceleration. Sometimes the rpm will go up and down a few hundred rpm in a jerking fashion if I hold the pedal steady where it was when this starts. If I let off the accelerater then re-apply the gas slower there is no problem. It is worse if there is a load on the car, such as, the A/C is on or I have a couple of passengers.

I have a code 41 for which I have replaced the TPS and adjusted it many times. The code does not go away. Cleaned the throttle body several times, also the ERG valve, ran many cans of Seafoam and BG44K, Replaced the in-tank fuel screen, the underbody fuel filter, the plugs,wires,caps,rotorsand coils. This all did help with better acceleration, but did not fix the problem.

I have been leaning toward the ECM as it will throw a code 41 also as well as the wire harness to the TPS will code 41. I also read that the fuel pump is a two stage unit. It has a normal pressure and a higher one for more aggressive acceleration. Anyone else heard of this? It was in a British car mag for LS400 diagnostics.

I am interested to hear what was going on with your ls that prompted you to replace the ECM and the Mass air flow unit. And did your car do this before the change? If not I would put the old ECM back in and see if it still does it.

If you go with the dealer please post their findings. There has not been any post except yours that matches my specific problem.

Good luck, Walt

See I cant replace the old ecm because the shop i sent it to kept it...they said the components were too badly "burnt" and were unfixable...so they replaced it with another used fixed ecm. The mass airflow sensor/unit was changed because the old computer was putting a code down saying there was a malfunction with it. The car hesitation didnt do all of this before everything was changed...only until i replaced the old ecm, mass airflow sensor, crank sensor, fuel filter, spark plugs, did the hesitation start. I'm bringing the car to the lexus dealership tomorrow and hopefully they can fix it...i will keep you posted walt.

im pretty sure the ignition coils are original. how can i determine if they are bad?

See pages 6 & 7.

onvehicleinspection.pdf

Here is a Link that explains coils and makes the point that a basic resistance test may test good while the coil may start to fail under load. I mention this because that was the case with our '94.

thanks LScott400!!

[scotty2hottyoki]

I have another question. Since my stock ecu I sent to Houston, Tx had traction control and they said it was unfixable...if they by chance sent another repaired ecu that DIDNT have traction control...and i installed it in my car..would that possibly make my car hesitate? Thanks

[LScott400]

I have another question. Since my stock ecu I sent to Houston, Tx had traction control and they said it was unfixable...if they by chance sent another repaired ecu that DIDNT have traction control...and i installed it in my car..would that possibly make my car hesitate? Thanks

I've never seen anything to suggest that there are different ECM's based on traction control.

You mention that plugs were changed, but not wires, caps, rotors or coils. It is possible that in pulling the wires to install the plugs that a deteriorated wire(s) did not hold up well under the stress. You could ohm out the wires with a digital voltmeter to check them.

I had a '94 with the exact same symptoms you describe in your initial post. The ECM had leaking capacitors and had eaten through the protective film on the circuit board. The replacement ECM totally cured the problem, but I knew I had good (recent) plugs, wires, caps & rotors. A few months later it developed an immediate problem of no acceleration under any conditions. A new driver's side coil fixed that. What I don't know is if the coil was part of the initial problem, but the ECM was enough to compensate causing the coil to finish dying.

If you don't have personal knowledge or receipts from relatively recent wires, caps & rotors replacement, then I would start there. If they are known good, then I would replace those 14 year old coils. If the problem is still not resolved, then I would contact the ECM supplier about how to go about getting a replacement. Fun ain't it? ;)

[GeeLs400]

Any results on this issue I’m having same problem with my 94 Ls400 I changed both ignition coils plugs and wires and had my ecm rebuilt still have same problem

[vissine]

On 11/30/2019 at 1:29 PM, GeeLs400 said:

Any results on this issue I’m having same problem with my 94 Ls400 I changed both ignition coils plugs and wires and had my ecm rebuilt still have same problem

I would try the steps that nc211 listed above first.