20v reving between gears

[Jeonsah]

Hey guys,

I have a blacktop 20v 4age with a haltech elite 1500. I got tired of dealing with my iscv so I decided to remove it from the engine.

Now when I shift gears, the engine will rev 500 rpm or so in between the gear shift. It is making smooth driving somewhat difficult. Also when the car starts up (hot or cold) it will rev to 3500 or even 4000 rpm sometimes. I am not sure what this issue could be. The huge vacuum port for the iscv has been blocked off with a vacuum cap.

Any ideas what could be causing this? I am thinking there is something letting extra air into the engine somehow.

Thanks!

[jondee86]

When you start the engine and the revs go high... what happens next ? Do the revs
stay high, or do they quickly/slowly back down to some lower rpm and hold there ?



Do you still have the vacuum servo "throttle opener" thing hooked up ? If that is not
adjusted correctly it can prevent the throttles from closing fully.

Cheers... jondee86

[Jeonsah]

When the engine initially starts, the revs go to 3500rpm or so and they drop back down (normal speed) to 1000 rpm and stay there. I had adjusted the idle stop (the one stop that controls all 4 throttle openings) to move the idle to where I wanted it (1000 rpm).

Is the vacuum servo the metal diaphram thing in the picture? I believe I have that hooked up correctly. I will confirm that tonight when I am home.

Thanks!

[jondee86]

I've never had a working servo (the round metal diaphragm thing) so I'm not
totally sure how it should work. But my understanding is that when the engine
is not running, there is no vacuum to operate the servo, so the rod extends
fully and pushes the throttles slightly open.

As soon as the engine starts the servo gets some vacuum from the manifold,
and the rod retracts far enough to let the throttle actuator arm sit on the throttle
stop. There is some adjustment on the rod, and the FSM specifies what rpm the
engine should be running at when the vacuum tube is disconnected (servo push
rod stays out while engine is running).

If the servo is working correctly, try adjusting the length of the rod to make it
slightly shorter. Do a couple of trials and see what difference it makes.

Cheers... jondee86

[Jeonsah]

Here are the pictures just incase:





On the rod there is a stop that controls the opening of the itbs throttle valves. That is what I adjusted for the idle.

[jondee86]

On the rod there is a stop that controls the opening of the itbs throttle valves.
That is what I adjusted for the idle.

I think that this is where the problem comes from. If you check the throttle actuator
arm between the middle two ITB's, you will find (hidden down underneath) an adjustable
throttle stop screw. This is for the arm that the throttle actuator linkage attaches to on
top. And that is the throttle stop that you need to adjust to crack th throttles open.

So what you need to do is back the adjustment off the throttle opener rod and set your
idle with the adjustable throttle stop. Then take the vacuum line off the throttle opener
and use the throttle opener rod adjustment to set the engine speed to 2500rpm or less.
Hook the vacuum line back up and go for a drive.

That *should* work

Cheers... jondee86

[Jeonsah]

Jondee,

This is the screw I had originally adjusted to lower the idle:



The throttle opener rod is not adjustable. So there is no way I could have messed with the throttle opener. I am thinking the the check valves for the throttle opener or the throttle opener itself is starting to go bad.... What do you think?

[jondee86]

I made you a pic looking from underneath...



Helps if you have X-ray vision

Cheers... jondee86

[Jeonsah]

Jondee, what would happen if I just removed the throttle opener diaphram all together?

[jondee86]

What would happen if I just removed the throttle opener diaphram all together?

You might have trouble starting the engine. All engines like a bit of extra air when starting
(especially when cold) and usually this is provided by the ISCV. If you have an operating ISCV
there is no problem with removing the throttle opener. However, since you have removed your
ISCV, the throttle opener is currently providing a bit of extra air for starting.

So you can either adjust it as I suggested, or take it off and maybe need to use a bit of throttle
to get it started. Same deal as the guys who block off the AAV on the 16V single throttle. Some
say no problem starting and don't mind the idle going higher as the engine warms up

Cheers... jondee86