The following problem has been bagging for almost couple years but I have had enough. To cut the story short...the power seems to decline by the day where it takes farther to push the pedal to get the car moving and the shifts change and become little bit rougher. HOWEVER, if I reset the ECU, most of the power gets restored (yes, WTF?). I have to reset the ECU almost every week in order to get the power back. The motor is definitely not close to its output and its apparent!

The car is close to 120K miles and just performed the following:

Replaced the spark plugs (I replace them with V-powers every couple years).
Cleaned the entire intake.
Made and installed a proper (baffled) Oil Catch Can.
Ran the annual BG44K treatment

Also in the past year or so,

Replaced the KS and Fuel Filter over the summer.
Replaced MAF with a stronger 5th gen couple years back.
Replaced the Cat with a HF Cat since the OEM was clogged with metal hair.
Replaced all ATF with Amsoil in the transmission last year (irrelevant?)
Replaced all coolant with Toyota Red with the ATF (irrelevant?)

I've done so much research but have come to zero conclusions. Some theories that make sense are clogged precats but wouldn't the decline be permanent? Maybe the O2 sensor(s)?

It defiently sounds like a electrical fault somewhere but my knowledge only extends to mechanical.

Any help is appreciated!

 

No idea what the issue is, but why do you change plugs every year? You should just be on your 2nd set...

 

Sorry I meant I change them every 2 years. It's the V-power's from NGK (cheap and readily available) so I don't expect them to last over couple years, IMO.

Iridiums are a whole another story.

 

You said the problem started about 2 years ago, and you also changed your MAF 2 years ago... could that be related?

 

Gizm0,

I changed the MAF because of the problem so I don't think they could be related. It was a brand new 2000 MAF and I transfered the little therm. onto the new MAF.

 

Have you ever messed with your throttle body while trying to clean it?

Does the loss of power happen only when the engine is warmed up? Or as soon as you start it?

 

What about the pre-cats?

 

I have cleaned the TB but I never pushed the butterfly. I just blasted the cleaner through the small crack between the TB and the butterfly.

I like to warm up the car atleast a minute for the transmission's sake so I don't know much about the cold/warm effectiveness to the problem.

Scott,

I don't understand how precats would play a role. It has crossed my mind that them being clogged causes power decline but this problem is active rather than passive.

 

As they continue to clog, they would make the performance worse. I know when I changed mine out they both had deteriorated noticeably. The only real indication (besides an occasional P0420 code) was that my car didn't feel as strong as it should for 255 hp.

 

I still can't figure out how that would cause some of the power to come back after reseting the ECU.

 

Do you have any CEL?

 

Nope. Surprisingly, in the 4 years of my ownership, I've never had CEL.

 

Does your CEL light work? Does it come on when you turn on the ignition but before starting the car?

 

Yeah it works. IT comes on and I triggered it by accident while working on the OCC.

 

this is what i would recommend you to do.

since you have to reset the ecu and you get your power back try not reseting it and see if you are getting the same mpg.... to see if it is cutting off how much fuel it takes in after.....
it is very hard to try and solve your probelm..... did you clean your maf???

 

What grade of gas do you use? Any knocking sound?

 

Damn that is weird when I had a power issue it was the precat clogged that was killing the performance for me but good luck hope you figure it out!!

 

I'll try to keep a tab. Thanks!

I've always used 93 but someone did put 89 once.

Yeah thanks dude but precats are the last thing I want to replace.