Need a Toyota guru 1MZFE Hesitation

[BMC1970]

2003 Lexus ES300 witht he 3.0 1MZFE motor.
Has noticable hesitation upon mid throttle acceleration. NO CODES
I noticed that the air intake boots after the MAF were dry rotted and torn. I replaced those this weekend thinking that was the problem.
Also cleaned out the throttle body as I had everything off. Put it all back together and test drove.
It was a slight improvement, but not enough. The hesitation is still there. When I want to put the throttle about midway down for an extra boost going uphill or on the highway, it will "lurch". power band goes down, then up, down then up. As if its being choked of air every half second.
When flooring it, the car will downshift and take off like a scared ape. Babying the throttle in town will not make the problem happen either.
Its always at the mid throttle point, when you need just a little extra oomph.

I ran my Driver scan app and there are no codes, and no check engine light.
The MAF g/s readings are in their respective normal range at idle and at revving to 2500-3000 RPM's. Those were the only parameters I could check.

So as of right now I'm totally stumped. Without a code being thrown I'm unsure where to look next. I just have a feeling its something basic thats not showing itself.
Looking for any and all suggestions.

 

[dumkid]

Something to do with variable valve timing being slow? Maybe a bad accelerator pedal ?

 

[snarl]

How are the plugs

 

[eljefino]

Watch your fuel pressure, could be a failing pump.

 

[Leo99]

I'd throw some fuel injector cleaner in and see if it improves. Techron has a good reputation.

 

[DemoFly]

This era of Toyotas will simply not throw a code for an ignition misfire. Check the plugs. Just because the plugs are new or newish doesn't mean there isn't a defective ground strap or cracked insulator.

 

[BMC1970]

Something to do with variable valve timing being slow? Maybe a bad accelerator pedal ?

I had thought of this too. But the lack of these items not throwing a code has me stumped

 

[BMC1970]

I'd throw some fuel injector cleaner in and see if it improves. Techron has a good reputation.

Did that. Waiting to see if it helps.

 

[BMC1970]

This era of Toyotas will simply not throw a code for an ignition misfire. Check the plugs. Just because the plugs are new or newish doesn't mean there isn't a defective ground strap or cracked insulator.

I used to also have a 2003 Accord that behaved the exact same way. Threw the parts bin at it, and nothing helped. Did plugs and coil packs on that too. Along with a host of other stuff. Never figured out what it was, sold the car. If it would've just thrown a code that would've given me a clue to start with. Similar to this Lexus.

 

[malibuguy79]

If I am not mistaken you should have a dual runner/volume intake with a flapper.

My initial gut reaction was intake boots. But you already solved that.

Next I would check that flapper and the diaphragm and associated vacuum line that runs it.

 

[ripcord]

A car that old is likely to have some deteriorated vacuum lines. I'd give those a good going over.

 

[joegreen]

Take a good look at the maf and clean it anyway. I had a 2000 es300 with the same engine that would periodically dirty the maf and cause hesitation issues.

 

[BMC1970]

If I am not mistaken you should have a dual runner/volume intake with a flapper.

My initial gut reaction was intake boots. But you already solved that.

Next I would check that flapper and the diaphragm and associated vacuum line that runs it.

I don't see a dual runner in this one. Just a single throttle body with one intake boot going to it. If I recall, earlier pre 2002 models had dual runners.

 

[BMC1970]

Take a good look at the maf and clean it anyway. I had a 2000 es300 with the same engine that would periodically dirty the maf and cause hesitation issues.

Forgot to mention that I replaced the MAF with a new one. Still no difference.

 

[BMC1970]

A car that old is likely to have some deteriorated vacuum lines. I'd give those a good going over.

Good idea. The ones I saw during the intake boot replacement process were all good. I also changed the air filter too.
But a good going over of the ones under the engine cover are needed.
No specific code being thrown is sending me in all kinds of directions.

 

[BAJA_05]

Plugs possibly like mentioned earlier. Run back to back tanks with Techron Complete Fuel System Cleaner.

 

[DemoFly]

I used to also have a 2003 Accord that behaved the exact same way. Threw the parts bin at it, and nothing helped. Did plugs and coil packs on that too. Along with a host of other stuff. Never figured out what it was, sold the car. If it would've just thrown a code that would've given me a clue to start with. Similar to this Lexus.

Or you could just check the plugs.

 

[Kurtatron]

So many part throwing suggestions. OP, you should get a realtime data anaylzer so you can read things like fuel trims, spark timing, and throttle position, things like that. If your throttle position sensor is bugging out, it could be causing other issues. But throwing parts is not a good idea. You can get decent data analyzers on Amazon for like $30. They plug into the obd2 port and connect to a laptop. On the laptop, you can read real time performance data. I would recommend that before throwing parts at it.

 

[Graham Piccinini]

MAF sensor. It's the MAF. A very common problem on many engine families of that era.
Remove the MAF, and clean it with a MAF Sensor cleaner or electrical parts cleaner. DO NOT use brake or carb cleaner.
My 2003 GS300 was doing it up until I cleaned the MAF correctly, and now it's all good. Same thing in one way or another happened on multiple Toyota/Lexus vehicles I owned in the past. Always the MAF. Never a CEL code. (until I actually unplug the MAF)
Cleaning helps most of the time, but on rare occasion a replacement is needed. Only buy OEM, if that's the case. (I see you already bought one. IS IT OEM???) But I'm sure a spray cleaner will bring it back around. DO NOT touch the MAF sensor with fingers. Any oil, including body oils will greatly accelerate its death.

 

[The_Eric]

Ancillary to this discussion, many people mention checking or changing spark plugs, but so few ever change or inspect the coil boots. I cannot tell you how many people will change the plugs(even 2 or three times) and not do the boots. With plugs going 100k miles all the time anymore, the boots start to lose their snug fit and fail to retain the spark energy, resulting in a misfire. I've fixed several "bad transmissions" with coil boots. Also fixed several "bad coils" too.

To the op, I don't know if you've got misfires or not, but if you think that you do, check/replace the boots.