Phusche

I have replaced spark plugs, new ignition coils, t-belt, and intake gaskets. This CEL issue flashes when decelerating 50-30mph and light acceleration 40-60mph. Engine doesn't seem to have any power loss and engine is smooth at idle. Appreciate any tips. Thank you in advance.

salimshah

Did the problem show up after the work [mentioned in your post] was done?

Salim

Margate330

If this all happened immediately after your repairs I would be interesting to see the fuel trims at idle and on decel.
The fuel trims should go negative(-) usually in decel as the ecm cuts fuel and be near 0 to +10 at idle(after car warms up).

Since you had the manifold off maybe a vacuum leak but I don't know- if the problem was the T-Belt install you would know right away when it threw a code so can maybe rule that out for now hopefully.

Phusche

The vehicle was running perfect and passed smog check (in CA) then a few weeks later this issue occurred

Phusche

New intake gasket was replaced

slothman

how many miles on it ? have you done a compression test ? low compression or valve issues can cause misfires. You have covered the ignition part, so I would focus on the fuel. Check the fuel pressure regulator. Run a good fuel injector cleaner. Check the fuel pressure PSI. Check for vac leaks.

• Clogged or faulty fuel injector (s)
• Intake air leak
• Fuel injectors harness is open or shorted
• Fuel Injectors circuit poor electrical connection
• Insufficient cylinders compression
• Incorrect fuel pressure

Margate330

Good list and more thoughts can I add...
That's another reason I like to see fuel trims because a lot can be seen sometimes like fuel delivery problems and vacuum issues.
And a vacuum gauge(Harbor Freight) Teed in with a 6 foot extra line so I can drive the car and watch the vacuum gauge laying on the dash for the needle to swing way up on decel to make sure the engine is breathing right.

I think the RX300 has a similar acoustic manifold to the RX330 and there is a valve that activates at a certain rpm powered controlled by a vacuum selenoid but this is one of the crazy things I was thinking of with the code popping up at certain accel and decel, don't think it would throw these codes or know why I'm buzzing around vacuum and fuel delivery but really hope it's not compression or valves.

Was also wondering about a failing/dying knock sensor based on engine load conditions/rpms causing issues with timing but the guesses can go on and on...

I like real codes that mean something! lol so hard to do anything with generic misfire codes...


On the RX330 this manifold flaps moves on accel and decel at certain rpms and this pic is for the RX300 and they are similar.
Don't know if the flap will move goosing the throttle at idle or if it needs to be driving the car over a certain speed or if it can cause codes in the right conditions with other stuff.

Add- I don't think this is the cause I just find it facinating on how the car does this and changing ignition timing and cam timing, etc depending on load, rpm, accel, and decel conditions- so much going on and calculations in real time!

slothman

most of the time these codes are spark plugs and coils. however could also be fuel injectors. I agree on a vac gauge, that will rule out air leaks. Fuel pressure gauge is also needed. In this case, I am putting my money on fuel related. Only because he has ruled out ignition.