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Good day gentlemen, I have been having problems with misfires since I bought the vehicle. It also was troubled by excessive oil consumption, which some of you may or may not be aware of. Toyota finally admitted their mistake a couple years ago and sent out a special warranty notice regardless of mileage for any vehicle that burns more than 1qt of oil in ~1200 miles, who is then eligible for an engine rebuild. Anyway, this may or may not be related to my misfire issue; I know little about the vehicle before I took possession, other than to assume that the previous owner did not religiously check the oil. It likely was allowed to burn much oil and run low.


The pertinent details and timeline is as follows:


Misfires occurring for years, throwing P0300 and P030X codes on random cylinders, P0016 popped up twice afaik
Misfires occur when idling; sitting with vehicle at idle will cause MIL to activate much faster than driving at hwy speed
(<30 min idling vs days to a week or more when driving with minimal periods of idle).
Idle speed is erratic but never stalls.
No real noticeable loss of power at any normal driving range rpm
Regular burning smell which I assume is from unburnt fuel/oil reaching catalyst


A year ago the vehicle went in to dealer for the special warranty coverage for excessive oil consumption for 2AZ-FE engine. After consumption test they replaced effected parts at no cost.

9/2016 Work performed for this issue included all new: (according to dealer)
Pistons
Short block
Chain tensioner
Oil pump
VVT gear
Balancing shaft
Balancing shaft bearings

I provided rebuilt cylinder head, which was installed during engine work


After engine work was done, immediately P0300, random P030Xs, and P0420 pop up, same as before
Returned to dealer for diagnosis; technician said the misfire could be due to possibly: coil packs, spark plug, fuel injectors, sticking valve in head, or bad VVT gear (VVT gear was supposedly replaced by the same guy a month earlier)
Front catalytic converter replaced, eliminated P0420 (rear cat is not clogged fyi)

Attempts to rectify P030Xs:
Front & rear O2 sensors R&R
Spark plugs R&R
PCV valve R&R
MAF sensor cleaned
Ignition coils switched out with new ones, no change
Inspected OCV, tested solenoid, appeared to function properly
(solenoid responded to voltage, did not seem dirty, disconnecting with engine running results in instant P0010 and no change to idle)


Recently P0016 re-appeared for the second time:

Inspected CMP sensor, appeared to function properly
(responded to metal proximity when hooked up to multimeter)
Could not locate OCV screen filter
Could not access CKP sensor (behind power steering pulley?)


Questions/Thoughts:
- If problem is due to VVT gear being damaged or “positive or negative” as tech suggested, why wouldn’t he notice that when he put the engine back together? (espc if he replaced the VVT gear as they claimed)
- What are the odds that the problem is in the new head, and was also in the old head, i.e. sticking valves?
- If problem is due to fuel injectors being clogged, why does it only effect idling?
- Others have suggested vacuum leaks may be the cause, is this possible?
- Could a clogged OCV filter cause all of this?
- Possibly CKP sensor? It always starts fine, sometimes a with a rumble.

I have no idea where to go from here, any help greatly appreciated!
 
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