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My power curve ain't right ('98 1UZ VVTi)

eicca

Member
This happens under anything less than full throttle. As the revs build, right at 3700rpm WHAM there's a sudden jump in power. It's a noticeable push back in the seat. I assume this is the ACIS switching to short runner intake mode.

The engine seems to be running fine, but I don't think this is the proper behavior. I feel like it should be a smooth power delivery regardless of RPM and throttle.

I've repaired several vacuum leaks, changed the spark plugs, cleaned the throttle body, all the usual preventative maintenance stuff. From my reading, I suspect the oil control valves may be not functioning 100%. Does this sound correct? I've also got a rough idle, not stumbly, but rumbly.

What else should I look at?
 

gloverman

Well-Known Member
It's easy to check the acis system is functioning. It's possible to see the lever on the back of the plenum and it should rotate when the engine is started.

I've had a couple of vvti actuator solenoids fail. To test their operation take them out carefully. Ive had local garages break them by being too rough. Apply 12 volt and earth to watch them move. They will have wear marks to indicate full travel. If they don't move both out and return freely its sometimes possible to clean them if it's from oil sludge. If they spark up and don't move check resistance of the coil windings. They should both be the same.

I've also replaced the cam pulley but that is a bit more checking. Good oil is also important. These engines normally idle very smooth. Lambda sensors are another common failure I see. Scan tool makes checking these easy.
 

eicca

Member
I'm inclined to believe the lambda sensors are ok since I can regularly get 30mpg on the highway. Is that sound reasoning? I'll happily check them anyway. What readings do I look for?
 

gloverman

Well-Known Member
It is sound reasoning but they can also be a indication of other issues. Check they are cycling but not giving excessive trims. If they go past the trim limits they will lock out and default to zero for a little while then repeat.
 

eicca

Member
Will do. Also, another thing that makes me suspect my OCVs aren't functioning 100% is my car has "moods." Some days it jumps off the line quite enthusiastically, others it's more lethargic. Thoughts?
 

eicca

Member
I haven't had time yet with work and all. I need to do that. Thanks for humoring me and playing internet mechanic in the meantime...
 

George_R

Member
Post more info on your setup (manual/auto, stock ecu or not, fuel pressure, a/t oil level, coolant level and all details like that). Do you feel like the problem is constant or intermittent? Do you see it both when the engine is cold and warmed up?
 

eicca

Member
Car is bone stock and all fluids are fresh and at proper levels. The jump at 3700rpm has been constant since I bought it, the "mood swings" happen every few days I would guess. The idle has been rumbly since I bought it. It's not loping or jumping rpm, the tach stays nice and steady, but I can feel it throughout the whole car. I imagine this is more likely the engine mounts than anything else.
 

George_R

Member
I'd recommend to check with scan tool first of all. ELM327 ver.1.5 + ELMSCan Toyota android app to start with. Won't hurt your pocket
What I would do: read DTCs stored in memory, check long term fuel trims (both banks) at idle and 3000rpm, perform active tests for vvti and intake flap
 

eicca

Member
Can I read the same parameters with Techstream? It's high on my shopping list and if it'll do the same I'll just get that.
 

George_R

Member
Of course you can if you can afford it along with proper adapter. Original OpenPortII would be best choice for its price though it's surely an overkill for you
 

eicca

Member
Update: since installing my modded intake tube (which is just the stock tube with the resonator removed) I noticed that the induction noise gets louder when the ACIS switches to short runner around 3700rpm.

Maybe that's normal because the long runners will muffle the sound?

Or could that be a sign of restriction in the long runners? I could easily imagine PCV oil building up in there since they start at the bottom of the manifold.
 

gloverman

Well-Known Member
I run them on the dyno to see if thw lever is moving. You could set up a camera. If it's moving when the engine is started then generally the system is working.
 

George_R

Member
You can as well activate it from your scan tool of choice or just by powering the valve directly from battery
 

George_R

Member
Undo driver's side head cover and see what's there
Yellow is ok
Lots of gunk => congratulations

Intake oil buildup usually isn't a problem by itself
 

eicca

Member
So I plugged in the Techstream today and got short term fuel trims around 2% and long terms around 19%. Those should be closer to zero right?
 
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