Idle screw adjustment on stock ecu

[curamrdan]

Hello, i was not sure where may i insert new thread, hope its ok that way.

Have myself tuned motronic ABY, stroker 2.5L, PKmotorsport cams(say similar to 7A), and modified throttle body(removed the wedge block from butterfly). Changed target RPM to 840 instead stock 740rpm + slightly enlarged "dutycycle" table for it. I inspirate this from MTM RS2 software.
Stopper screw butterfly shaft has been already adjusted several times, so i dont know factory position.
TPS switch is working.

It idles nicely. But after xx km of driving, when im moving in traffic jam or just move car a little few times, rpm jump to 1500 for a several second and starts to regulate back to target. In worse scenario it bouncing few times 2000-1500rpm and then regulate back.
It happends again after few km or situation depending.

Recieving error 00533 - idle speed regulation (adaptation limit surpassed)

I can live with it, but there is no factory service guide how to adjust the stopper screw, can anybody help?

[UrS4boy]

N71 ISV and dash pot info

Your problem is nothing to do with the idle speed screw (which by the way, as far as I know, nobody ever has to touch from the factory setting). The issue is either a broken dash pot (which affects the closing speed of the throttle when you take your foot off the throttle pedal) *OR* the N71 Idle speed stabilization valve (ISV) has an issue - OR both.

The dashpot should not prevent the throttle from closing completely - at which time the N71 Idle Air Stablization valve takes over.

N71 Info: http://forums.quattroworld.com/s4s6/msgs/21853.phtml

Throttle info: http://forums.quattroworld.com/s4s6/msgs/20405.phtml

Dashpot (on an example AAN, ABY/ADU similar):

[curamrdan]

Thanks for your reaction.

My screw is in non factory position, unforutnately. It was randomly adjusted by prevousion owner and also me, to keep old damaged engine even run and avoid stalling.
My bet is, that screw is too much extended (to make more air).
There are some ISCV values at VCDS, with labels some of them are in range, some of them not. But need a clue what exactly may i see at VCDS to be ecu happy.

Dashpot has ok diaphrame, it was just 1mm less preloaded, according pdf guide with 5.5mm drill bit. As i understand, drill bit may be inserted to a stopper not stopper "idle" screw, right?

[twoqu]

On a stock throttle body the screw protrusion is @3.5mm if thats of any help!

[curamrdan]

On a stock throttle body the screw protrusion is @3.5mm if thats of any help!

Thank you, where did you know it? My is very slightly over 4mm drill bit :/

[twoqu]

Thank you, where did you know it? My is very slightly over 4mm drill bit :/

I have one of the car that I measured!
Of course the screw should not be adjusted thats why it is covered with a tamperproof cap. The idle should be controlled by the ecu.

[curamrdan]

On stock car is no point to adjust. But ecu still count with some base settings from factory(therefore there is a adjustment) and then it just control the rest by ISCV and some adaptation over time.
Problem is on modified engine, there must be the mechanical base settings adjusted to suit the engine. For better understandment, as my experience from other factory ecu, hot engine, no coolant fan running with unplugged ISCV = set in some base opening and throttle screw is set to idle for example 700rpm. And after that, ecu will count with this base settings to make counted movement of ISCV to reach expected target rpm.

I know, iam repeating myself. Now i know, that my first attempt will be little loose screw by few decimal of mm.

[Error404]

Why do you need to adjust the idle speed? Unless you have some really lumpy cams there should be no need to jack the throttle open and I am sure that MTM did their adjustment in the map
I am not sure how Motronic works, if there is ignition based idle control as well as bypass air. I am sure PRJ can tell you

[curamrdan]

Primary question was to fix 00533 error and random rpm jump. And extra 100rpm is my(and MTM? ) opinion, smoother running, more oil pressure.

Ignition control is good point. It mixing issue even more. But im not too far from flawless settings , i think.

[twoqu]

From what I understand the throttle blade is completely closed so all idle air is controlled via the ISV duty cycle. So if the throttle is open because the screw is further out or the the idle switch is out of adjustment then the ISV control will be effected.
I undertand why you want the higher idle speed but as Error has said it should be able to be provided by the ecu. You could have got a low tech higher idle by spoofing the air con signal to the ecu. The inner workings of the Motronic are a mystery to most of us mortals.

[martinjs]

Going from your pics your throttle cam has disintegrated and your cable is tie wrapped in the wrong position.

[twoqu]

You can also check to see what the ecu is seing via VCDS from the idle switch. Think its group 4. The display should change from idle to part throttle.
When you removed the wedge from the throttle plate did you fill the holes?
Need to start eliminating potential causes and possibly invest in one of Martins nice throttle linkages!

[curamrdan]

Going from your pics your throttle cam has disintegrated and your cable is tie wrapped in the wrong position.

Yes cam is damaged, and have not catch. So i tied it to have correct play and reaching closed and full throttle stoppers. Im 100%sure this works ok, just is ugly.

twoqu: holes are welded of course. Idle switch according VCDS is ok, but its old part, it can miss the beat on 1click of 100 for example. Billett cam is nice, no doubt

[curamrdan]

I have an idea, so back this thread up again. Is there somebody helpful, with fully stock S2/RS2 , just to warm up the car and unplug idle valve to see where rpm idle rest? Im expecting around 1100-1200 rpm . If so, then idle screw may be set same way to this level. Unfortunately i have noone around, with "unmolested" car.
EDIT: i did it on my car, idle was between 1000-1200 rpm depend if car is moving or no. So just window where idle is on stock car, can be helpful.