DriftingB26RX7

iTrader: (4)

good i was high, but what i ment to say is that...your revs go down because you have p/s and you are using it....if you dont have p/s this will not happen!!! and the only time this happens is when your car is just sitting or moving under 5mph

J-Rat

iTrader: (2)

You arent any smarter when you arent high, then when you are...

WAYNE88N/A

Lol...

How come nobody's mentioned the ABPV? Isn't it supposed to energize when the steering switch kicks in?

apeckz

Many n/a 2nd gens have ECU problems that effectively reduce the voltage that is sent to the BAC. There are one or two writeups about this along with instructions regarding the replacement of a transistor that often fails in the ECU. Unfortunately, the instructions deal only with the s4 ECus . I replaced the transistor in my s5 ECU that has the same circuit identification number as the s4 but got no improvement - I continue to suffer reduced idle when any load is put on the engine (lights,rear defrost, heater fan, etc.)

Find the writeup - I think it was by P. Stoaks - it includes a test that will indicate whether your problem is in the ECU.

If you find someone who can trace the BAC circuit in the ECU you will probably find one or more circuit components have partially or completely failed. PLEASE post if you do find someone who can fix these ECUs or post instructions for us to follow.

J-Rat

iTrader: (2)

Yes, but IIRC, thats only on the TII. Its on the backside of the TB assembly, and is activated by the PS computer. Provides less then a 100 rpm drop when the car is steered lock to lock WITHOUT MOVING.

I think the N/A relies on the BAC? Or maybe the AWS valve? Or maybe I need to look in the FSM?

Either way, when your car is steered while parked you will experience a SLIGHT drop in RPMs, but it should not kill the car. Hell, I have my BAC disabled, my ABPV disabled, and I run on a Haltech that I havent even enabled any idle control, and my PS only drops my idle about 100 RPMs.. And I have 225 50 R 16s up front..

Food for thought.

J-Rat

iTrader: (2)

Pin 1R on the S4 N/A ECU...

WAYNE88N/A

The ECU doesn't send voltage to the BAC. The voltage comes FROM the BAC side of the circuit, and all the ECU does is cycle the ground to energize the valve. This is why you get a falling voltage the more the BAC is energized (the higher the duty cycle, IOW) when you read it at the ECU pin...

Rat- as far as I know, the ABPV on the NAs activates during steering switch activation and when the AC button is pushed on...It's not on my car any more, so I can't test that out (neither is AC or power steering, for that matter)...

SonicRaT

iTrader: (6)

I've never seen an ABPV on an N/A, where are they located and which series?

WAYNE88N/A

Maybe the terminology I'm using is confusing everybody?

On the left aft side of the dynamic chamber, with the two large air hoses (one comes off of the metal air bypass tube on the back of the TB, the other goes into the dynamic chamber). Held onto the dynamic chamber with two bolts...

On the wiring schematics, it's called the air bypass valve. And the relay that energizes it is called the air bypass relay. Both fed by the main relay...

Maybe the FSM calls it something different, like the AWS???

J-Rat

iTrader: (2)

Yeah, thats AWS, but its not used in the PS circut, near as I can tell.

WAYNE88N/A

Nope. Called the air bypass valve in the FSM also. In my '88 FSM, page 4-63. Only thing I can gather that's it's responsible for from the tests is the accelerated warmup system (even though my car still goes to 3K without it, lol)...

I'll search further...

I think everybody here calls it the AWS, and that's what led you guys astray

J-Rat

iTrader: (2)

I dont care what you call it.. It doesnt control the Power steering.

WAYNE88N/A

But I care what I call it

Only thing I can find in the FSM says "assists BAC during cold start operation", so I guess that's all it's for- the AWS. That means we don't even need it on our NAs, because the BAC gets her up to 3K on its own (except for Hailer's car, his is broke and only goes to 2300 without the APBV)...

DerangedHermit

Would removing the emission equipment affect this at all? I'm having this problem too. Before I check the stuff mentioned here, I'd like to see if that's the problem.

NZConvertible

That depends what you removed. Some people remove perfectly useful idle control equipment because some clown told them it was emissions controls.

DerangedHermit

Well it was Kevin Landers, so I doubt he took anything off that would mess up my car. Guess it's another problem.

Icemark

what has not been covered yet, (despite three pages of meandering posts) is that a bad power steering computer will cause the idle to drop as well.

When the steering angle sensor tells the power steering computer that the steering wheel is turning, the power steering computer sends a signal to the ECU. Voltage of the signal is based on steering position, so the ECU boosts idle through the BAC based on what the power steering computer is telling the ECU the amount of force being exerted to turn.

With a bad power steering CPU (often cold solder joints) the signal does not get sent, the ECU does not boost.

Of course an aftermarket or stock steering wheel mis-installed will mess up the position sensor and can cause a simular problem, but the power steering CPU will set a error code and default the amount of boost and signal to the ECU.

NZConvertible

What Kevin calls "emissions" removal includes removing all of the factory idle control systems. Apart from the AWS (which I recommend removing) these systems are nothing to do with emissions at all and are there to make the engine idle properly. If you deliberately remove all of your idle controls, you can't really complain about a bad idle can you?

Mark, the PS computer has no control over idle speed. On S4 NA's and S5's the PS pressure switch on the pump sends a load signal directly to the ECU, which raises idle speed accordingly. On S4 Turbos the pressure switch activates the ASV via the PS relay to do the same thing. The PS computer doesn't have an output to the ECU.

DerangedHermit

Eh, so it goes. I'll trust his judgement.

TexanSeven

I have a pretty dumb question about the ASV. Can the nipple be open to amosphere, or does it need to be capped? I see no difference on my car either way...