[sorry for my English]
Hi,
There is a strange problem with 2ZZ-GE engine on my 02' Corolla.
Symptoms:
- At 2000 RPM fluctuation is like slow wave, once per second. At higher engine speeds - time decreases.
- From 2200 to 2300 RPM engine extremely vibrates
Checked ECU, no faults, cleaned whole air induction system, IACV, throttle body, etc., checked VVTL-i valve and filter, perfectly clean, checked hoses for air leaks, found one tiny leak, fixed, changed to a new MAF (OEM, Denso), changed to a new primary oxygen sensor (OEM, Denso), changed to a new spark plugs (Denso IK22, 1 step colder than OEM), reset ECU. Result - no changes at all.
Diagnostic check output:
50 seconds RPM log
50 seconds MAF log
50 seconds short-term fuel trim log
Long-Term fuel trim -12% at idle and -5% to +5% while driving.
Both old and new oxygen sensors are slow, 6 times per 10 seconds at 2500 RPM.
Why could it be? Maybe thats the reason?
Thanks.
My 2ZZ has a small idle fluctuation like that also, but it idled smoothly with new plugs and a new passenger motor mount. I also have a new upstream sensor around 90K as part of maintenance. Clean the TB, MAF, replace the plugs with fresh Iridium plugs, I found the Denso Iridium Twin Tip plugs to be the best I've used so far.
Already done that 
I have found that fluctuation wave of primary oxygen sensor signal is equal to short-term fuel trim and RPM itself. Both old and new oxygen sensors works at same rate, 6x per 10s @ 2500, while minimal allowed rate should be more than 8x. Thats why ECU creates these fluctuations. What could be the reason for this behavior?
- insufficient heat and/or exhaust gas flow? why and how?
- failed VVT-i valve, creating effect like open EGR valve and lowering exhaust temperature? I tryed to check it, but it doesn't want to come out. Should I try to take it out by force?
- leaking injector? LTFT -12% @ idle, but this shouldn't have effect on exhaust temperatures
I don't know, I think it might be normal. My 2ZZ does exactly the same thing at 2500 RPM, a slow but regular up and down tick in engine speed with steady throttle. It never does it when the engine is under load and driving though, not that I've noticed. It's small, less than 100 RPM and the oscillation increases with engine speed but is not noticeable at idle to me at all.
I don't think it's normal, because these oscillations comes from oxygen sensor signal, which is "faulty" according to 2ZZ-GE repair manual. But it isn't. Thats interesting and should be investigated further. I will try to clean injectors, check fuel pressure, search for exhaust leaks and check VVT-i valve in next few weeks.
I used a Denso O2 sensor that should have been the same as what I took out. I hear/feel the same thing when running 1ZZ Corolla's in the shop. No O2 sensor codes are thrown and my 2ZZ performs perfectly. Maybe under load it switches faster? Maybe there's an ill defined bit of translation, like my old 93 Prizm that per the manual was supposed to get 90 Octane fuel (but they meant 87, RON vs PON). Or maybe it's like when they toss an insufficient switching code for a bad thermostat because there's a mis-definition somewhere. I don't really think it's a real problem unless you're having a problem or setting a code. I'm still going to be interested in what you find it anything.
How badly does your VVT sprocket rattle btw?
My VVT-i sprocket seems ok, no noticeable sounds from it.
Update1 - fuel injectors:
Got lower milage (120 000km) injectors, cleaned in ultrasonic bath and installed them. There were no noticeable changes in RPM fluctuations or vibration of engine. Next thing to try is replacing PCV.
Update2 - PCV valve:
Replaced to a new OEM PCV valve. At first LTFT got much better (from -12% to -4%!) on idle and acceleration was really smooth, but next day everything returned back, so it was coincidence. Next (and last) thing to try is complete VVT-i system check and repair.
