Darby42164

I have been reading the forums and everyone is very helpful and knowledgeable I thought I would post my care issues. I have a 92 ES300 that has a weird intermittent misfire. In the morning while cold, it starts and drives fine, no misfires. Even after driving for several minutes and the engine warms up, no misfires that I can detect. If I stop the car for 20 minutes and restart, it misfires at idle and the car shakes when under load at 60 mph going up a hill (more misfiring I am assuming). It may misfire at slower speeds under load but the vibration may be just less detectable I assume. It will continue misfiring till the car is turned off. Next day start it up cold, no idle misfires, no misfires or vibrations under load at 60 on a hill. While misfiring under load at 60 mph on a hill happens at 2-2.5k rpm. If I give it gas and get rpms up to 3K or higher the vibration stops (or I can't detect it).

I have taken this to the mechanic and had the spark plugs replaced, spark plug wires replaced, plenum gasket replace, cap, rotor, fuel filter, air filter replaced (there was oil leaking from the cap and rotor), rr plenum gaskets and rr vc gaskets and tube seals replaced (this is what it says on the bill, note I am not a mechanic so I don't understand all this). No change. The mechanic seems baffled. He wants to put another set of new spark plug wires in the event the new ones were defective. This has not been done yet as I was running out of money for just trying things. There is no check engine light, the mechanic checked for codes and there are none. Misfires continue as before with no change. He used NGK plugs.

While the mechanic is willing to continue searching till I am broke, I was hoping for some guidance on just where the problem might be for a more targeted search. Does this weird misfire pattern ring any bells with you folks who have knowledge or experienced such a thing? Thank you so much in advance for any advice.

tomf

A bad O2 sensor can give random misfires. Have you ever replaced yours? This is something to consider especially if you haven't replaced them before.

I'd be cruising at 70 mph or so and there would be a random misfires. Like you, if I gave it gas the misfire would seem to go away. Eventually the misfires became so bad at all speeds the car was undriveable.

You won't get misfires when the car is not warmed up because the ECU is not using data from the sensor until the sensor reaches a certain temperature.

Also bad knock sensors can cause random misfires.

Darby42164

I have not changed the O2 sensors. Is this something that can reasonably be done DIY? Or best left to a mechanic? This sounds like a potential solution for the problem.

I have fleshed out the symptoms my car is having which are a little weird to me. As I said in the morning while the engine is cold, there are no detectable misfires. What is weird is as long as I keep driving the car on that first drive, there are no misfires, even when the engine has warmed up. I have driven the car for over an hour after starting it cold and no misfires. Turn the car off for ten minutes, restart and it is misfiring in idle and in motion. Do you think an O2 sensor might account for such odd behavior? I was wondering if it was a computer issue (or computer issue with a sensor) on start up. I was wondering if the computer got one signal on start up cold that results in no misfires through out the drive, where starting warm sends a wrong single to the computer that results in misfires for the whole ride. But I am not an expert and am guessing here.

Oh I should have put in the first post that my car has 60K miles on it. FYI.

Thanks so much for the advice!

tomf

One of the reasons I suspect it could be the O2 sensors is that the ECU does not use data from the O2 sensor until it is warmed up, about five minutes or so.

O2 sensor are a DIY project on the 1mz-fe engine. I'm not sure for you because you have a different engine, 3vc-fe. But I think it's similar. Maybe someone with that engine could chime in.

Here's one way to do it from the top of the 1mz-fe engine. https://www.clublexus.com/forums/es3...00-w-pics.html

I usually put my car on stands and access the bank 1 sensor 1 O2 sensor from the bottom. The bank 2 sensor 1 O2 sensor is easily seen by standing in front of the car and looking down. It kinda looks like a spark plug.

O2 sensors usually last over 100,000 miles. You only have 60,000 miles. But your car is 23/23 years old!

My comments are about the 1mz-fe engine. You have the 3vc-fe engine. Keep that in mind.

tomf

FYI: The O2 sensors for your car cost about $41 each on Amazon for the two upstream sensors and about $56 on the one downstream sensor..

ES300NZ

overly sensitive knock sensors 'could' cause something like this too. The oil thins out when the car is warm, tiny amounts of knock / vibration (of no consequence) show up, tripping the sensor, which causes the timing to be massively retarded (in both senses of that word).

Other possibles are;

Bad / failing fuel pump
Blocked fuel filter.
Water in the fuel. (add .5lts of meths to tank).
Bad fuel (low octane).
Bad earth wire/ earth connection failing with movement. (check main lead from engine block to shell/body)
Bad battery,
ruined exhaust muffler blocking flow. (heavily rusted on the inside ?)
failing alternator / half charging.
Air intake box full of debris (leaves / etc).
Vacuum leak, in the intake piping (check for cuts in the ridged section / breaks).
engine valve(s) sticking open.
possible bad engine mount ? or gearbox mount. (with other things?).