Setting up aftermarket DBW throttle body...

[jaffaz32]

few years back i purchased a Blox 72mm DBW throttle body for my car.

When i installed it, it worked a treat.

About 6 months later it started to develop a idle issue, the revs would drop too low and stall and they would no sit stable, the revs would bounce at idle.

So i took it off...

At the weekend, i thought it's just sitting there lets get it on and see what's up with it.

there isn't any vacuum leaks from what i can see.

The factory throttle appears to have 3 adjustment pins. 2 based around the motor which alter the closed butterfly position, not sure about the other. And there is one on top which is a idle control valve.

The Blox only has the two around the motor and not the Idle control valve.

So...

After some experimenting and looking at the factory unit vs the Blox I noticed that the butterfly on the factory unit has a good few mm of play before there is any resistance from the motor. With the motor bolted on the Blox does not have this play. There is resistance from the word go. So I assume the bouncy Idle must be down to the lack of freeplay, what i am guessing is that the motor for what ever reason must twitch hence the freeplay on the factory and the bouncy idle on the Blox.

Based on that theory i adjusted the freeplay on the Blox so it had as close as i could get freeplay to the factory unit. It appeared to resolve the bouncy revs! However! this same adjustment affects the position of the butterfly in it's closed position, you can probably see where this is going, once adjusted the car wouldn't idle at all without any throttle and just stall. Perhaps it's a case of getting the sweet spot between freeplay and idle but i'm doubtful that is the case.

I previously changed the TPS on the blox and set it up with a voltmeter based on info from service manual, that didn't work either.


I can't think what else i could try, any suggestions?

It's just really frustrating i have this sitting around doing nothing, it's a well made billet throttle body and 72mm vs the factory goose neck.

 

[L_RAO]

The Blox TBs are notorious for quality-control issues on the clearance-side of things.

My 74-mm Blox had issues too.

The throttle plate would stick or get caught inside due to variations in the expansion of the throttle body when warmed up.

My solution was to take a metal sponge (or some sandpaper), and simply sand down the edges of the walls of the throttle body cylinder (the tube that the throttle plate rests/operates in).

No issues since.

 

[Old Guy]

Since you are installing a DBW throttle body, I am assuming that you have a later model DBW ODBII car and make all my comments on that basis. The stock DBW throttle body does not have an idle air control valve. All idle speed control associated with warm up, air conditioning, ... is done through the ECU controlling the servo motor on the throttle body. The screw on top of the throttle body (its oriented 90 deg to the bore of the throttle body) is the idle adjustment screw and I will make an educated guess that it is merely an air by-pass that allows for a controlled (adjustable) amount of air flow around the throttle plate when the throttle is closed. The idle adjustment screw is used to set a base idle speed for the engine.

I have never seen a Blox throttle body; but, if it does not have an idle air by-pass circuit (the idle adjustment screw), it needs some other mechanism for allowing air past the throttle plate when the throttle is closed to set the base idle speed. Otherwise the engine will not idle. Perhaps the Blox has to be set up with the throttle plate slightly open in which case you are going to have to adjust the TPS to reflect the new fully open and closed positions. I suggest that you refer to the installation manual for the Blox throttle. Since the Blox throttle does not have an idle speed adjustment screw, the set-up procedure in the NSX factory service manual will not be applicable.

 

[jaffaz32]

The Blox TBs are notorious for quality-control issues on the clearance-side of things.

My 74-mm Blox had issues too.

The throttle plate would stick or get caught inside due to variations in the expansion of the throttle body when warmed up.

My solution was to take a metal sponge (or some sandpaper), and simply sand down the edges of the walls of the throttle body cylinder (the tube that the throttle plate rests/operates in).

No issues since.

It's a little sticky going from fully closed to slightly open.

In my case it has issues when the engine is hot or cold. I don't think the sticking is causing my issue.

That is a good idea though, will give it a try.

- - - Updated - - -

Since you are installing a DBW throttle body, I am assuming that you have a later model DBW ODBII car and make all my comments on that basis. The stock DBW throttle body does not have an idle air control valve. All idle speed control associated with warm up, air conditioning, ... is done through the ECU controlling the servo motor on the throttle body. The screw on top of the throttle body (its oriented 90 deg to the bore of the throttle body) is the idle adjustment screw and I will make an educated guess that it is merely an air by-pass that allows for a controlled (adjustable) amount of air flow around the throttle plate when the throttle is closed. The idle adjustment screw is used to set a base idle speed for the engine.

I have never seen a Blox throttle body; but, if it does not have an idle air by-pass circuit (the idle adjustment screw), it needs some other mechanism for allowing air past the throttle plate when the throttle is closed to set the base idle speed. Otherwise the engine will not idle. Perhaps the Blox has to be set up with the throttle plate slightly open in which case you are going to have to adjust the TPS to reflect the new fully open and closed positions. I suggest that you refer to the installation manual for the Blox throttle. Since the Blox throttle does not have an idle speed adjustment screw, the set-up procedure in the NSX factory service manual will not be applicable.

My car is obd1 but with dbw.

It does have a hole inside the throttle body at the top just like the factory unit. On the factory unit from memory this hole sits on top of the butterfly when closed, on the blow unit it's in front of the butterfly. Perhaps this is the air that passes through?

On the back of the factory unit there is a hole which looks like a bypass, the blox unit doesn't have this either. I'll get a pressurised air duster and blast the hole and see where it comes out. Perhaps it's blocked and as you say is causing it to stall.

That's a good point, now I've adjusted for free play I might need to adjust the tps accordingly.

The blox never came with any instructions, it's a one off, well technically one of two made I believe.

 

[Old Guy]

If there is an idle air bypass, the inlet will be located upstream of the throttle plate and the outlet will be located downstream of the throttle plate. Normally there would be some kind of tapered screw type adjustment to allow you to set the air flow through the bypass and the resultant idle speed. Otherwise, your idle speed could be uncontrollable (really high with no way to reduce it if the bypass admitted too much air). Since your TB is a two-off, I am thinking that it is more likely that whoever made it never bothered with the bypass circuit and figured it would be just as easy to set the idle speed by adjusting the servo motor so that the there is a gap around the throttle plate to admit air when the throttle is closed (not sure how you would do that). I think that would work provided you adjusted the TPS to read closed in its new 'closed' position. Not sure whether this might screw up the idle control functions associated with warm-up and air condition which are controlled by the servo motor / ECU (at least they are in the OBDII DBW, not sure about your OBDI DBW).

That is my best guess anyway!

Update:

I am thinking that setting the base idle speed by adjusting the throttle plate to provide a gap may result in very bouncy idle speed if the ECU is trying to set a fast idle during warm-up. At small throttle opening, small changes in throttle plate opening probably make for big changes in airflow (control system speak - high forward gain) which is going to make it a nightmare if the ECU is attempting to keep a steady engine speed during warm up. If the ECU just opens the throttle a little more to speed up the engine and doesn't attempt to regulate the speed, then everything should be more or less OK. Well, maybe less OK; but, still workable.