Idle adjustment?

[hyperkinesis]

Hi. I want to know how adjust the idle to optimization the rpm and throtle responds.. And some help if the idle valve adjustment have something to do to car running rich or leen. Thanks for the help

[schumicat]

you need to say what year you have.

[hyperkinesis]

sorry, is a 1984 carrera

[Chuck.H]

You change the idle speed by modifying the DME software. The idle air bypass only sets the 'base idle'... the final idle is set by the computer by modulating the idle air valve.

Now, you can override this, and set the base idle higher than the computer is trying to achieve, but you may see other problems from this, like way high idle during cold start.

HTH,
Chuck.H
'89 TurboLookTarga, 348k miles

[Nostril Cheese]

Take off the oil cap with the engine running. Does the idle change?

[rusnak]

yup. The idle is set by the DME chip.

The popular thought that you can adjust the idle with the bypass is actually just making the ICV work more or less hard to maintain the same idle. The bypass screw should be only adjusted with the ICV centered.

You might want to try disconnecting the "bridge to ground" but don't forget to re-connect it again at smog test time. An aftermarket exhaust and perhaps chip would be your next consideration. But then you'd have to have the right gas all the time.

[hyperkinesis]

yes with out the oil cap the idle change...

[E Sully]

Idle on the '84-86 is programmed for 800 rpm. Attempting a higher idle speed with the stock chip will cause the idle to surge up and down. Later '87-88 chips were programmed to 880 rpm. The procedure is to put a wire jumper in the port by the engine console with the engine warmed up. This bypasses the Idle Control Valve, and then set the idle manualy to 800 rpm. You also need to make sure the micro switch on the throttle body is set correctly.
The idle dropping when the oil cap is removed is a good indication there are no vacuum leaks.
Setting the base CO level is also important.

[T77911S]

what he said.
check it, set it, or leave it alone. you gain no performance here.

[rusnak]

Sully, that's an interesting note about the DME's adaptive memory.

I deduced that there had to be some sort of memory when I encountered a no start with my flywheel change. I wrote about that on Rennlist at the time.

Idle adjustment: jumpering the two contacts centers the ICV vane. Then the idle speed screw is brought into spec at idle. This adjustment allows the ICV maximum range to work, maintaining idle through commands from the DME.

[Chuck.H]

Interesting indeed - AFAIK, these '84-89 DME's have no NVM (non-volatile memory) and every start is as if it's the first time ever it's been started...

Just curious - what manual did this come from?

Chuck.H
'89 TurboLookTarga, 348k miles

[MConn]

Good information, Ed. I never noticed this before.
I found this in the 911 Bentley Service Manual for 1984 - 1989 on page 240-4



Mike

[CraigDseattle]

I am curious to know if there is a good starting setting for the idle setting screw. For old school carbs, there were rules of thumb, like close the mixture screws down, the open them up 1 1/4 turns as a bench setting before doing your carb adjustment.

Is there a similar tip for an idle setting starting point for 3.2 Carrera motors

[DRACO A5OG]

nope, idle on 3.2 is controlled by the DME, so it is critical you set the base idle as described above so the dme will not have to over work to maintain the proper idle for the installed chip.

[CraigDseattle]

How can you tell what chip is installed in the car?

On my thread about surging and O2 senors, the point was made a couple of times that idle settings are dependent on the chip. As far as I know, mine is stock, but I should probably verify to be sure I dial everything in properly.

Thanks!

[kidrock]

Craig, you'll need to pull your driver's seat and pull your DME computer to find out what type of chip you have. Here's Steve's page with details on how to do this:

911Chips.com - Motronic Chip Installation Instructions

If it a stock chip, it will simply have a number on the chip starting with "911xxxxxx". If it is a Wong chip, it will have a "911Chips" sticker on it. There are other aftermarket chips that will clearly have the chip make printed on it.

[JAR0023]

Only way to know without a doubt what chip is in your car is to pull the DME and open it up.

One thing that helped me wrap my head around setting idle has already been mentioned. You are not so much adjusting the idle up and down (though you can) as getting the throttle body and DME in sync. The DME knows where it wants to idle. You can adjust up or down but you are making the ICV work to do this and it can have unintended affects if you get too far out of range.

I can't remember if I picked it up here or in the Bentley, likely here. Once you set your idle and pull the jumper there shouldn't be a change in idle if you have it correct. This makes sense since jumpering the ICV sets it to the middle of its range. I just went through and corrected some small vacuum leaks and had to reset my idle. FWIW my 86 is happiest with idle set at 780 rpm and it is rock solid there. If I try to bring it up to 800 or more I get a sporadic idle bounce on cold days as the car warms up.

-J

[CraigDseattle]

Here is what I posted yesterday in my thread about idle surge and O2 sensors -

With all the suggestions, I decided to investigate the base idle setting situation.

I started by checking the idle switch by sound and by multimeter, then I checked resistances at the ICV terminals - - all looked good.

I drove long/hard enough to get all warmed up, and watched the idle rise and felt the surging/hunting slowing increasing. I popped in the jumper (BTW a 3.5mm mono jack fits great), and messed with the "screw" shown in the picture below. I was looking for an idle adjustment screw like on an old carb, but there is none. This seems to be the adjustment for the base idle speed.



With the jumper in place, and the O2 sensor connected, the surging was apparent, and I ultimately had to really screw the hex head "screw" in quite a was to get the idle to soomth out in the 800 - 850 rpm range.

Question - what is a good "bench setting" for this screw? Like close to the right, then backoff to the left by X turns.

It seems that mine was very far out, and I rotated it in quite a ways to get the idle where it should be. When I removed the jumper, the RPM dropped 50ishRPM, but seems to be running and idling really well.

So now, with O2 sensor connected, fully warm idle a bit less than 800 rpm, there seems to be no surging and the performance feels really good all around.

I don't know how/why my adjustment ended up so far out, and I hope I havent totally missed the boat on this adjustment.

With the screw - is right/in lean or rich? is left/out lean or rich?

I'll get her out on the road tomorrow to see how things go.

++++++++++++++++++++++++++++++++++++

So, if the idle dropped a bit when I remove the jumper, does that imply I'm not in the sweet spot on the screw adjustment? Should I try to fine tune that, or does it sound like I'm okay?

Like I said, that screw was pretty far out, and as I turned it clockwise several turns, the idle surging went away so that seems like improvement.

My other question relates to where/how to hook up a tachometer/dwell meter in the engine compartment - is there a 12V spot to power up the tach?

thanks for all the ideas!

[CraigDseattle]

Howdy -

just a bump on this thread to share some more info and questions.

thanks

[Chuck.H]

>>With the screw - is right/in lean or rich? is left/out lean or rich?

Neither - this is an air bypass screw, it just lets air past the throttle body. The DME will set the mixture accordingly.

Moving this screw simply adjusts the 'base idle'; from there the IAC (Idle Air Controller the cylinder shaped thing near this screw) will modulate additional air to stabilize the idle, and raise it during cold starts.

Turning the screw out allows more air past the throttle blade. If it's turned out too far, the IAC can't lower the idle enough to get to 800 RPM. If it's in too far, the IAC cant raise the idle high enough during cold starts.

HTH,
Chuck.H
'89 TurboLookTarga, 348k miles