legacycentral bbs

If you'll recall my jerky throttle thread here, I said my car would jerk under the most gradual throttle application.

I thought about it some more and remembered that my throttle-body stopscrew (the one set from the factory that you're never supposed to touch) is still waaaay off on my TB when I was a dumb kid and decided to play with it. I tightened it so much that I broke the head off of the screw, and the remainder is still sitting in there, way too tight.

I theorize then, that there is a possible overlap or delay between the IAC valve closing and the engine receiving the air from the TB, since the ECU has now altered the IAC valve's duty cycle to compensate for it.

My question then: Is there a way I could remove the throttle body, do a thorough cleaning of it while it's off, then take it to a machine shop, perhaps, and have them bench test it for the factory flow rate at idle, then put a new screw in there tightened to the proper setting, and then swear Scout's honor that I won't touch it again?

You really can't replace that sealent that's in the TB.

You're just better off getting a used one. I've got a few laying around I think......There's a guy on the USMB that could probably get you one really cheap too.

Would it fix your bucking problem.....ehh....I'm not so sure.

Josh, do you mean sealant between the TB and manifold? Isn't that just a gasket?

He means the black goo stuff that goes around the throttle plate. There is a thread about it.

MK

mTk wrote:He means the black goo stuff that goes around the throttle plate. There is a thread about it.

MK

yup...what mk said.

Alright, so cleaning the TB is only going to make matters worse. Can I still remove it and take it somewhere to be set back to factory specs, or do you think it's better to just swap in a used one...

I think your theory sounds plausible. The adaptive idle control system was meant to work around changes in the engine's volumetric efficiency and stuff like that, not to work around miscalibrated throttle bodies or IAC valves. Subaru's official position is that if you modify the calibration you have to replace the part.

A problem with trying to have your throttle body set back to factory specifications is that nobody really knows what the factory specs are.

Also, the amount you'd pay just to have access to a flow bench for the necessary period of time would probably be about the same amount you'd pay for a used throttle body that has never been tampered with.

So, I agree with Josh -- the best way to go would probably be to get a used good throttle body. Get one with the TPS still installed intact so you don't have to go through the process of calibrating the idle switch, too.

A new throttle body gasket is part number 16175AA150 and should only cost a couple of bucks.

This has not been brought up yet, so I assume it's false reasoning. But is a throttle body set from the factory independently of the engine, or is it set depending on that particular engine's specs? In other words, could a throttle body be misadjusted when installed on a different engine?

I guess I'll just hafta find a good throttle body with factory-set TPS and stopscrew...

Hmmm, as the saying goes, when you replace, upgrade. Does an EJ22T TB have any distinct advantages over an N/A?

Thanks for the help guys!

I believe the throttle body is calibrated independently of the engine; otherwise, how could Subaru sell you a replacement throttle body after you've tampered with your factory one?

The turbo and non-turbo throttle bodies are the same.

so you should get boostjunkies tb

Okay, got a TB off eBay, nothing is touched on it, although I'm just assuming the TPS is functioning properly. What kind of sealant should I use on the gasket to the manifold, or should I use sealant at all?

Just use a new gasket; that should be fine.

If you want to apply some of that aerosol copper spray, you can, but no sealant is necessary.

Just use the gasket.

You may want to check the tps.....for its idle switch and make sure it's working properly.

I might dig out the multimeter and act like I'm testing it. When I see some number pop up, I'll pretend like I know it's in spec and put it in

Haha, I'll probably just bolt it on, and if there are problems, I'll know what it is.

Thanks for the help guys

vrg3 wrote:I think your theory sounds plausible. The adaptive idle control system was meant to work around changes in the engine's volumetric efficiency and stuff like that, not to work around miscalibrated throttle bodies or IAC valves.

This is exactly what was happening...

I found time to swap throttle bodies (delay at the dealer on ordering the gasket ), and did an ECU reset right after installing it. Car idles absolutely fantastically at 750rpm. Doesn't shake, dip too low, spike too high, nothing. No CEL, so the TPS must be good. And the jerkiness is gone, so my theory was indeed correct.

And the whole thing cost me $20