Hello,

I got a 2001 4Runner w/ 5VZFE at around 197k miles from my father. Since then I've replaced:

-Valve Cover Gasket - 200k
-Spark Plug Wires (NGK) - 200k
-Spark Plug (NGK) - 200k
-PS/Alt/AC Belts - 205k

At 212k, it's been running well but the radiator hasn't been replaced by PO so I decided to replace it (Denso and Zerex Asian 50/50). I opened the timing cover and realized that there are some cracks so I decided to replace those too (Aisin kit w/ tensioner)

This is my second Timing Belt change on a car (first was a 94 Miata). I made sure the Belt marking for cams line up withe the cam and cam marks at TDC, and at the brank, another belt marking with the "dot punch" in the crank gear. I rotated it two full turns and Cams and Crank are still lining up so I pulled the tensioner pin and put everything back together. I made sure that crank bolt torque is 217 ft-lb with a torque wrench that goes up to 250. I plugged the cam sensor attached to timing cover back

Upon startup, I noticed that the engine is running really rough. I scanned it the first time and it has a pending P0300. Then as it warmed up, the engine smooth out and back to normal. So i decided to brake in the brakes (I also did Tundra brake swap) and was fine the whole time.

Got back home, turned it off. Then couple hours later, I turned the 4Runner back on and it's rough again, this time the P0300 showed up w/ CEL. No other codes. Then as it warmed up again, the rough idle went away and it drove like normal.

Any culprits? I tried searching but a lot say it's wires and plug, but those are only 18k and there were no issues with the 4runner at all before i did timing and radiator.

tldr:

-12k ngk pug and wires
-replaced radiator (denso) and timing belt (aisin)
-rough w/ p0300 only when cold

Thank you!

-Randy

Where did you purchase the NGK wires and plugs? (tons of fakes out there)

-Charlie

Yeah, it's gotten so bad I only use plugs from the dealer now. I would verify no vacuum leaks. Check all hoses and ensure the intake plenum is torqued to spec.

Vacuum leak?

Weird not getting any email notification

I got the spark plugs from eeuroparts at eBay (99% w/ 8k positive) and the wires from Amazon (direct from Amazon). I've been burned before so I always make sure the ratings are not just high, but also plentiful. It eliminates some doubts for me from the seller.

Update:
Hooked up the smoke machine, found the known cracked hose (big hose right before intake throttle) and replaced it just in case. No other leaks that I see. I turned on the 4runner and exact same problem still...any other possibilities?

The intake plenum is good too. I replaced the actual throttle body about 4 years ago as it was throwing CEL and made sure it was torqued to spec. Never had problems.

The weird thing is this P0300 really just came after I did the radiator replacement and timing belt change

They may not even know they are reselling fakes to some people. Those two sites are spewing more and more counterfeit parts these days. I'd use Rock Auto or another dedicated parts vendor. May not be your issue but don't rule out the possibility. Denso has a whole tutorial online about spotting fake plugs from shady vendors.

Thank you i'll keep this in mind. I just bought NGK spark plugs too for my wife's Crosstrek from them couple weeks ago but haven't installed it yet

At this point, its not hard to pull the plugs and check condition.

I still put money that at least one of those sources sold you some counterfeit stuff...

-Charlie

Update, resetted ECU today and now P0300, P0303, P0304. The two middle cylinders

Plug wire routing? Again, I have little faith in eBay plugs. Maybe swap those two plugs into a different pair of cylinders.

There was a recent thread about melted spark plugs.. So be careful where you buy it. One of the denso I bought from sixcityauto on ebay (a legit dealer selling denso products and have purchased about 30 plugs from them) failed.