2005 Mazda3 2.0l 5speed.
Had the car since July, it's been painfully slow since I bought it, the rear O2 sensor is missing, no bung on the pipe, sensor wire cut off half way. The check engine light is always on and figured the car was always in limp mode. Anything past half throttle the car got slower, if I pumped the gas pedal twice a second as the RPMs climbed once in a while it would accelerate properly until shifting gears. (Continuously pumping the pedal = 50 times or more, once in a while = 1 in 100 times, so once in 5000 times flooring it, it would accelerate).
Recently the gas millage got worse and I finally pulled the codes. 4 came up, 2 for the rear O2 sensor, 1 for Evap system and DTC P2006 -Variable Shutter Tumble Valve Stuck Closed.
The workshop manual diagrams are vague and I search the VTCS removal threads for info and pictures of the system.
While inspecting the system I notice the shutter valve actuator and lever sat near the top of the throttle body with the engine off. once started the lever was down but never came up even after hours of driving.
From what I read, once the engine is at operating temps it should remain opened.
I had no idea which way the lever needed to be for the shutters to be opened and after removing the throttle body to check the actuator I decided to just pull the intake manifold off and remove the shutters and shaft.
I did not take any pictures because it was raining and my hands where covered in grease and dirt but for all those asking where the manifold bolts are just google images. I didn't bother, I just figured I would keep removing stuff until the manifold came off and it did.
I did however find the perfect image for this but I can't post links or images because of my post count.
The best I can do is post this: ww2.
Connect the ww2. to the rest and paste it in the address bar.
The image shows the assembly inserted from the passenger side but to remove the shaft it comes out next to the throttle body. The image also shows the position of the 8 bolts that hold the manifold to the engine, 6 are highlighted blue and the other two are next to the throttle body flange.
Some things I decided to do (possibly been mentioned in the 68 pages this thread has turned into):
1- I removed the shaft and shutters with as little damage as possible in case I had to put them back but I decided to grind down the 8 half circles that remained in the "cups" (4 black plastic pieces that sit in the manifold and hold the gaskets in place). They are there to transition the air over the shaft when the shutters are opened / to direct the air into the shutter when shut and act as a stopper to limit the shutter travel in both directions. I ground them for 2 reasons, 1 they are a huge airflow impedance even with the shaft and shutters installed and 2 the shutter actuator rod limits the shutter and shaft travel (if I had to reinstall them).
2- I felt that something was missing in the process in all the How-To's I read, I could easily understand every step (even without pictures) what I couldn't understand is what blocks the holes between the runners after the shaft was removed? Maybe I missed that step in the write ups, but it seems to me all I read was members that had done the mod repeating remove the shaft and shutter flaps and put everything back together and on the car the way it came off. Which would mean those that did the modification that way did something wrong, you cant have large holes between the intake manifold runners constantly scavenging air from the other runners to the valves that open, that messes up the whole flow of the manifold, why have runners if the all share the same air.... I used 1+ inch pieces of 1 awg gauge wire, it fit snug between runners 1&2 and 2&3 but it seemed loose between 3&4 and 4&end (this one is a factory vacuum leak), so I wrapped the wire piece in electric tape (not recommended oil passes around there and will turn the tape to goosh and maybe suck it through the engine but this is a 347$ car and I was sick of searching for stuff that fit in the holes...).
I am happy to say removing the shaft and flaps (and blocking the holes) solved the acceleration problem, the car has been running with the shutter flaps permanently shut since I got it and so by deductive reasoning the fault lies with the solenoid valve or wiring to the solenoid valve, from what I can tell when vacuum is applied to the actuator it shuts the shutters, if mine is staying shut all the time then the solenoid valve is not cutting air flow when it's supposed to, I will test the solenoid and wiring and still fix the problem to clear the cell.
Unfortunately I have no before to go by, I have driven other Mazda 3 2.0l 5speeds but all I can remember is they are slow, this car went from golf cat to smart car because the shutters where no longer stuck shut.
Could it improve performance, absolutely without a pile of junk in front of the intake port resisting flow.
Does it matter on a 14* horsepower car, absolutely not. Even squeezing 40 more hp still isn't worth the effort, it would be like showing up with a slightly smaller soft ball at a baseball field, you still don't get to play with the big boys.
I was tempted by habit to take a die grinder to the intake ports and port them out, and looked at the throttle body and thought, that's at least a 12mm shaft the flap sits in, with the average flap being 2mm thick that means each side of the shaft is 5mm thick or 5mm flow restriction, as a basic throttle body mod on some cars I pull the flap out, cut the upper half of the shaft off with a hack saw, reinstall the flap and screws and cut the extra thread off the screws. may seem like a small thing but say the TB hole is 2.5", removing 5mm of obstruction across would be 13% flow increase over factory, on a 2" diameter hole 5mm would be about 21% flow increase over factory.
But to me it wasn't worth the time and clean up. This just isn't a car worth modifying for too many reasons, to name a few, the components are too delicate, link kits, tie rods, shock mounts, control arms... So say the engine was easy to tune and with a reflash, some injectors and a turbo you could run some serious boost (not at this compression ratio and not on these engines) then the clutch and transmission aren't up to it and so on.
Back to the VTCS mod, to do it properly you want to grind off the 8 half circles and plug the holes in the 4 inserts flush with the edge, I did not do this I just blocked the holes in the manifold and reinstalled the inserts. Having flush edges without any recesses where the holes are is best for airflow.