Speedtoys

What section has this in the WSM?

I have the CDs, just having trouble finding this.

I have all the throttle stuff put together, and i have to have the new TPS adjusted ALL the way to one way, and I had to back off the idle position screw about one thread to get it to consistently..positively..ALWAYS click into idle setting at closed throttle.

just wanna make sure theres nothing else I missed

Ed Scherer

I'm not sure where in the WSM that stuff is covered, but you might find Borland's post on this topic (the second half, the "For my S4" part) useful.

FWIW, I did the Dynamic kickdown mod when I did my intake refresh and followed Borland's TPS adjustment advice. It's been working just fine.

IcemanG17

there really isn't an idle adjustment like in early 928's....

I found the best way to set the TPS is to set the idle so it barely "clicks" ...that tends to allow the WOT to work too....if there is too much play in the idle...then WOT won't work which makes a bunch of other problems....plus the WOT is silent....you can only test it with a spanner or theo tester that Bill has...

I must admit....OB's are easier to work with in this respect...

Hilton

TPS adjustment is easy - you can hear the audible click of the idle microswitch, so just screw the throttle cable tighter until it doesn't click when you let go of the arm at the quadrant, and then back it off slightly so it clicks again. Test again when the engine's warm as slight expansion may interfere with it.

There's no idle adjustment on LH2.3 (87-95 928's). Its computer controlled to a specified idle depending on the contents of the chips. Stock S4 should be 675rpm (at last 5 speed is.. auto might be different? its in the WSM), GT is higher, 750rpm IIRC, due to lumpier cams.

A battery disconnect forces idle adaption - however if your car has an O2 loop, you may find it takes a short drive for the idle to stop hunting, as the computer compensates for MAF signal using input from O2 sensor to update the compensation cells in memory. I converted one of my cars to have an O2 loop (it has factory cats too now), and it takes about 5 miles from a cold start for the idle to stabilise after a battery disconnect.

For non-cat cars, adaption is a few seconds

John Speake

You shouldn't need to reset the thottle plate adjuster screw, which was preset at the factory. There is a risk that the idle control loop won't be able to hold idle correctly if you have moved it. There are no setting proceedures for that screw in the WSM or tech info by year that I can recall seeing. I think it must be set at the factory with a feeler gauge or a residual flow rate.

Do you think someone has touched it before ? There was a thread on here a few months ago when someone in the UK couldn't get the idle speed down, that turned out to be due to someone previously tampering with that screw. If you believe it hadn't been adjusted previously, and you can remember how much and in which direction you have reset the screw, then I recommend that you put it back where it started.

Then find out why your closed throttle switch can't be set. It would be better to slightly enlongate the slots of the switch than adjust that screw. But that shouldn't be necessary.

stevedavies

Speedtoys, read my previous thread on high idle problems. You should not need to move the idle screw ( unless someone has been in there previously). In my case a PO had adjusted it ( ie opening the throttle valve) so much that the automatic control couldnt bring it down. The idle screw defines the throttle plate opening. There are some good pics showing what it should look like.
The TPS position on mine was almost on the limit in one direction of the adjustment. This is normal ( based on the original TPS which I removed).

Speedtoys

My original TPS at the adjustment limit is able to click in and out of 'idle' setting fine...barely.

The brand new one..needed a hair pulled OUT of the adjustment screw to get a click in & out consistently & confidently.


Of course, that little plastic roller that moves inside the slot for the throttle shaft from the accelerator cable lever..has some play in it.

I imagine if that was less worn, it would pull BACK on the throttle arm in that slot better, pulling things back to idle a lot better.


To your note: "There are some good pics showing what it should look like."


Where?

John Speake

Here .... https://rennlist.com/forums/928-foru...ht=stevedavies

about 3/4 way through

Speedtoys

_perfect_

I was following that thread..it all comes back now.


Will adjust at TPS as required.


Danke!

Speedtoys

Ok..the idle available vacuum port is fully clear at idle/closed throttle now, and TPS clicks in and out with what feels like much better margin now.

Mike LaBranche

Right on... keep up the great work. You'll have the BWAAHHHH here pretty soon, my friend.

Speedtoys

Soon...Im gotta go shop for tomorrow now..dangit.

But..water bridge on, oil filler neck, cam covers after shoppin is done..then I have a couple fuel lines to dremel apart and refresh..bout it.

callgeorge

Need help ; 1986 with high idle; I have reviewed multiple posts; I am needing pic of idle adjust screw--can't seem to find it on my vehicle. Appreciate any help in advance. Thanks.

John Speake

It's lurking beneath the crossbrace, about the middle - a 1/2" dia knurled adjuster with a screwdriver slot. Turn anti-clockwise to increase idle speed, IIRC

PorKen

Front of throttle body. You'll need a 7mm socket on an extension (black handle in pic). Turn CW to lower speed.

You may have a vacuum leak, often a loose plenum hose is the problem.