About three to four weeks ago, I noticed that my beloved 2004 LS430 daily driver started to have issues accelerating under moderate to heavy throttle. I thought it was just bad gas that I was running so I waited to see how the next tank was - only to have the same result. Added some seafoam - no improvement. The problem just seems to be getting worse.

The symptoms - car has serious trouble accelerating under moderate to heavy pedal, especially uphill. Fuel economy on the highway has gone from 28-29 mpg to 22-23 mpg. At moderate pedal, the engine starts shaking pretty bad. No error lights have come on.

Today, I took the car to my mechanic who ran a full driving diagnostic on the car. No error codes at all and all sensor feedback was nominal. Checked the fuel pressure is normal. FYI, the car idles smooth and will run. While driving, the transmission does shift smoothly. Just for good measure - we cleaned the MAF sensor today with no improvement.

I am at my wits end. Called Lexus directly and they told me to take it to the dealer.

Somebody please help me. At this rate the car will not run at all in a week or two.

 

Joshlee73...Welcome to the Forum. As you have 1 post, there is much for you to learn from this forum. I understand you are under duress, but please be assured the LS430 does not just die! Read away as there are many many threads to help you as well as an experienced independent mechanic.. There is no one on this Forum that can tell you with absolute certainty what your problem is. Many issues will not show up as error codes for our cars. If you had and error code, we might be able to lead you in a specific direction. I don't want to give you any possibility of what it might be as there are so many variables MAF? Oxygen sensor? Drive by wire issue? Of course there will be members to suggest to try this or that. If your mechanic cannot find the issue, it might be worth while to do a diagnostic at Lexus for $99+ and go from there. Good luck and please let us know how you make out.

 

Have you tried replacing the maf sensor? If it's defective, cleaning it won't help. Or have you tried resetting the ECU (unplugging battery for a few minutes)?

 

You waited a full month? Take the advice and have Lexus do a diagnostic.

 

You have any ideas when the spark plugs were done? Also check the air box make sure everything is well connected, check for vacume leaks, a fuel injector might be clogged, have them hook a smoke machine up to the pcv system and see if any smoke comes out of places it's not supposed to, that is just off the top of my head. As others have stated it is hard to diagnose a car without seeing any of the symptoms.

 

lsdude, when they ran the driving diagnostic today, the mechanic said the MAF feedback was right where it should be but we cleaned it anyway. And no, I have not tried resetting the ECU. I will try that in the morning. Anything to worry about when disconnecting the battery?

Spark plugs were done about 10k miles ago - replaced with OEM type plugs.

I have appointment in the morning to drop the car off at the closest Lexus dealer to me.

 

Just disconect the negative battery terminal for 20 mins and It will reset everything just then reconnect it and your good to go.

 

A bad ignition coil would give you an error code

 

How many miles are on the car? Could it be plugged up/overheating cats? Have you gotten down on your belly to observe everything underneath when she's up to full operating temperature? You shouldn't see anything red or glowing while looking up. It would be nice if you had an infra-red laser type thermometer, to check the temperatures of fully hot cats. I have no idea what the 'normal' temp of the exterior/metal guard of the cats should be. I'm sure RKW has a book or illustration though, lol.

Seriously, I'm thinking plugged cats, even suuuuper duper dirty or restricted air filter? Anything crazy like cold air intake? Is the car totally stock? Any mods or tuner or performance chip, etc?

 

Totally stock LS430. Air filter was cleaned about four months ago - K&N.

My mechanic said that a clogged cat would throw a code.

 

Lots of talk about how K&N filter oil will cause problems by finding its way onto the delicate MAF, but you said you cleaned it (hopefully with MAF CLEANER spray, nothing else)

Did the issue start after you did the K&N filter or not really? I know the LS will run terribly (at least mine did), when the air box and air piping and associated resonator, etc, were not installed. Double-check to make sure everything is connected properly, starting at the air box & resonator.

How about the throttle body/butterfly valve/gasket? Did you have anything apart related to that area of the intake?

I didn't see your response to how many miles you have on it. How many miles? If you have 100k+, I'd immediately do the coolant temperature sensor. Good aftermarket is about $20, Lex/Yoda about $60 and it's an easy DIY, and can solve many mysterious issues. I'm betting on some sort of sensor (air or coolant) or plugged cats.

 

Be cautious taking the car to a dealer... Better to go out on Yelp and find a high rated independent in your area that specializes in Lexus or Toyota. Maybe some members that are in SC can recommend a repair shop. Mileage and how well the car has been maintained all play into the factors. The K&N air filter that uses oil is problematic and have not seen many in use on the LS (many have discontinued the use of these...).

All the other advice given above are good options to try.....

 

I'm in SC, Cola. There is an indy in Broad River that specializes in Lexus.

 

Anything with a maf sensor can be damaged by the oil in those filters that I why I purchased a injen intake with a "dry" filter

 

I guess how many miles the LS has will remain a mystery.