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Discussion Starter #61 (Edited)
MAF, timing, temps, etc.
Can you be more specific? Are you referring to the MAF volumetric efficiency and the ignition timing advance? Also, I plan on checking the OCV filter.

Also, I've noticed that the drop in power occurs when I press down the throttle past 50%. Any less than that and it feels fine. Again, this only happens in the 2k-3k rpm range, so it can't be the tps.

Is there anything I can definitely rule out?

On another note about the orange stain on the spark plugs (from NGK's website):

Corona Stain: A removed spark plug sometimes has discolouration around the insulator surface which looks like gases have leaked between the insulator and the shell. This discolouration is generally called "Corona stain" and is caused by the fact that oil particles in the air around the insulator surface are attracted by the corona discharge, are charged, and then adhere to the insulators surface. The corona stain causes no deterioration of the function of the spark plug.

 

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Electromagnetic Wave :-h
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As a potential oil burner, its possible that you are getting a healthy dose of oil in the cylinders at that point, causing stumbling, and then it burns off. Its just a thought.

What kind of fuel are you using? When was the last time you ran some injector cleaner through?

Any of the sensors that impact fuel mapping/timing... like IAT, ECT, MAF, O2, TPS, etc. are the ones to graph.

I'm a little stretched here to be of much more help. Most of the Celica hesitation issues are MAF related. In the case of a GT, the intake manifold gasket is common. As are oil fouled O2 sensors/cats.
 

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Bring on the 12's...
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I still randomly get light hesitation in lift. Tends to be smoother and go away when I rectify a vacuum leak. But then I seem to manage getting more cracks in the piping and I"m back to square one again.

idling at 1500rpm on a noisy engine like mine is not cool.
 

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Discussion Starter #64 (Edited)
As a potential oil burner, its possible that you are getting a healthy dose of oil in the cylinders at that point, causing stumbling, and then it burns off. Its just a thought.

What kind of fuel are you using? When was the last time you ran some injector cleaner through?

Any of the sensors that impact fuel mapping/timing... like IAT, ECT, MAF, O2, TPS, etc. are the ones to graph.

I'm a little stretched here to be of much more help. Most of the Celica hesitation issues are MAF related. In the case of a GT, the intake manifold gasket is common. As are oil fouled O2 sensors/cats.
I'm using regular 87 octane. Should I try 93 or could that hurt the engine? I've ran injector cleaner twice in the last 6 months. No noticeable difference. I'm really starting to think it's my timing again. Thanks for all the help so far.
 

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Electromagnetic Wave :-h
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Brand name or off-brand fuel?

Timing problem would not limit itself to 2-3K RPM. A VVT issue might.
 

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2-3K RPM, from memory, is when VVT starts getting a lot more active, however if commanded and actual position were diverged by enough for long enough to affect engine performance it should set a code.
 

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Discussion Starter #68
2-3K RPM, from memory, is when VVT starts getting a lot more active, however if commanded and actual position were diverged by enough for long enough to affect engine performance it should set a code.
No codes here. I've checked over and over again, and it definitely only happens between 2-3k rpm. And the loss of power occurs with the throttle past ~50%. After 3k, it's smooth sailing. I've NEVER experienced the hesitation on the highway. What could affect VVT-specific performance?
 

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Electromagnetic Wave :-h
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were diverged by enough for long enough to affect engine performance it should set a code.
I think that's either '02+ or '03+. I don't remember which.
 

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Hm? VVT performance and range codes would be present for any year.
 

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I may be mistaken. But, there were codes added in later MY's.... I've forgotten if it was Lift or VVT. Air pump & DBW codes were also added.

Yeah, looks like P1349 has been around since day 1.
 

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Its the P0010, P0011, P0012 that were added...... another one, I don't remember the code, was a circuit supervisory on the VVTL OCV similar to the P0010.
 

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Discussion Starter #76
So, I thought I'd update this thread. I'm still having major hesitation issues.

As 2way suggested, I've replaced the OCV screen/filter with a brand new one. The old one didn't look that bad to begin with. Needless to say, this didn't solve my problem.

I also did a compression test and got 181 psi across all 4 cylinders. The engine seems healthy enough.

I also sprayed down the entire intake manifold to re-check for leaks. Nothing.

Another thing I noticed is that the hesitation is 2x worse with A/C on. The car accelerates like it's running only on 3 cylinders with it on.

I'm running out of ideas here.
 

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2KGTS (old man) installed a honeycomb in his COBB intake and it magically fixed so many problems he was having.
 
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