Bruno DeSousa

i have a suspicion the PO messed with this idle screw.. how can i re-set it to factory spec ?

would this screw cause a running rich issue if it was all the way open?

thanks in advance guys!

Bruno DeSousa

no one knows??

j.kenzie@sbcglobal.net

There are two idle adjustment screws. One 3 millimeters Allen head which controls idle mixture. There is also a 2 centimeters slotted screw which controls the amount of air bypassing the closed throttle plate, and thus sets the idle speed. You should set idle speed first. If you have vacuum leaks all of your adjustments will be off
Good luck
Dave

Bruno DeSousa

uhggg why is this car so annoying!.. i didnt see a allen head screw anywhere!? i have 1981 Ljet car.. if you are speaking of the screw on the AFM.. i think it hasnt been touched.. however the screw in the front of the throttle housing near the temp sensors might have been messed with... is there any specific way as to to how this should be reset? my car runs extremely rich.. i have addressed all the obv issues.. ive been on this forum for weeks getting advice... im down to this idle screw and possible a bad distributor and or cap/rotor.. i have done everything else.. i mean everything!!

j.kenzie@sbcglobal.net

Sorry for your trouble, Bruno,
The Allen screw is on the afm. To set the large idle speed screw, try turning it in all the way. If the idle speed doesn't change, you may have a number of issues. Vacuum leaks or temperature sensor telling the ecu that the car is too cold. The afm itself may also be faulty.
Good luck
Dave

j.kenzie@sbcglobal.net

Btw, there are three temperature sensors on the car.
Temperature 2, which measures coolant temperature, and may call for a richer mixture when cold.
Temperature 1, which measures intake air temperature, is built into the afm, and makes small corrections to mixture.
Thermostats switch , which controls the cold start injector.

For a rich condition, I would check temperature 2.
Dave

mark kibort

get the idle up by using the screw... then your richness problem might be found with the temp II sensor. measure the resistance of it when cold. (or hot) and let us know the results. something like 2k ohms cold and 400 ohms when at room temp.
doubt that the AFM was messed with , unless it was.
how do you know you are rich? rich at WOT as well, or just loading up with fuel when idling? and no, the idle screw has nothing to do with mixture. is your o2 sensor working? disconnect and see if idle smooths out and goes up a little. connected, there is a little idle hunting that is normal.

Bruno DeSousa

I know you guys are just trying to help so excuse this rant.. i am venting... it gets very annoying when i keep getting the same responses over and over.. and it gets old repeating myself over and over..

i have done all the obv stuff.. i.e, vacuum is fine, temp sensors have all be checked.. etc etc etc... i know im running rich because my eyes burn from the raw fuel coming out of the tail pipe when the car is idling along with the black smoke when i throttle the pedal..

i feel like im chasing my tail...

i just want to know how to re-set the idle screw because i am running out of possible culprits and i have a reason to believe the PO had messed with it... if that doesnt do much for the running rich issue... the only other potentials i have NOT yet tested are the distributor/cap/rotor... everything else is pretty much looked at and sorted...

thanks and im sorry for ranting.. this car is making me walk in circles.

z driver 88t

Bruno, The air-fuel mixture adjustment for the L-Jet is shown in a picture on page 24-6 in the WSM, Volume 1A. I don't know what the Rennlist policy is on posting a link to be able to download the WSM volumes (possibly copy written material), but if you don't have them, Google search "928 WSM Download," and it is the first link to pop up.

You need a long allen wrench to reach it. Something like this. It helps if you have access to a wideband O2 to help fine tune it. http://www.ebay.com/itm/Audi-80-90-P...9d24cc&vxp=mtr

Hold On

The idle SPEED screw is the large one at the front center of the intake. Slowly and EASILY turn the screw in until engine stumbles or stops. Back it out until things smooth back out and IDLE Speed stabilizes at approx. 850rpms in park.

The IDLE MIXTURE screw is the very small, difficult to see, spring loaded 3mm, special tool required one, that may still be covered with the factory metal plug. Located at the base of the AFM . The IDLE MIXTURE screw will only effect the A/F ratio AT IDLE. After idle it has no effect.

If your rich condition still exists off idle at speed, this screw is not your problem. Check the functions of your WOT throttle switch on drivers side of intake, make sure both wires are connected and you should be able to feel or hear switch clicking with engine off. Check the WSM for exact specs on this switch. Switch can be tested for continuity with a meter.
There is also a second switch at the same location the operates when you take your foot off gas and back to idle. Check that one also.
Hopefully no one had the AFM off and opened up prior to you owning car. That is also an adjustable sweeper arm the sends the signal to the ECM based on throttle position and air flow thru the AFM door.

j.kenzie@sbcglobal.net

Bruno
You are getting answers that seem odd, because you're asking an odd question. How do you reset your idle screw? You turn it until it's how you want it. I assumed you did that and it didn't work. I therefore gave you some other things to look for.
Good luck, you're on your own now.
Dave

Rob Edwards

Idle speed, WSM 24-5:



Idle mixture, WSM 24-6:

mark kibort

yep, that idle mixture screw does very little and almost nothing for part throttle. idle change will do nothing as well, besides change the idle.

sounds like its something else. leaking injectors, too high of fuel pressure due to faulty regulators?

or something up with ECU.

be nice to see what the fuel ratios are with a wide band analyzer.

j.kenzie@sbcglobal.net

Sorry guys, Bruno has checked all that. Oh well.
Good luck

ltoolio

As a n00b here who most certainly does not know everything and who tries to learn from the guys who know a hell of a lot more than I do (and apparently repeats themselves over and over), I wanted to document what I think I understand from this post so I know how to handle the situation should it ever occur on my '82:

Issue:
- OP has observed his '81 running rich, as evidenced by the burning eyes sensation he gets via the exhaust. This is experienced both at Idle and with Throttle.
- OP has requested information about "resetting" the idle screws as a possible resolution.

Troubleshooting by OP:
- OP has stated that he has done all the "obvious stuff", as mentioned in Rant Post #8.

Suggestions from (helpful) community:
- Idle screws only impact idle speed and AFM at idle. Therefore, this should have no bearing on the fact that the car is seeming running rich under throttle.
- Temp 2 sensor could be causing the rich condition if it is faulty, as it could be calling for a richer mixture even if the car/coolant is hot. It was suggested that resistance readings could be helpful, but they may have been covered in the Obvious Stuff already.
- O2 sensor could be the problem
- WOT switch could be causing the issue if it is faulty. Testing is detailed in Helpful Post 10.
- Leaking Injectors or too high of a Fuel Pressure.
- Possibly a bad ECU
- A Wide-Band Analyzer could provide more concrete numbers for analysis.

Summary:
- The original request of Idle Screw Resetting should have nothing to do with the underlying issue of the car running rich under all conditions.
- The answer might lie somewhere in the suggestions listed which are not in the intersecting portion of the attached Venn Diagram and are not in the "Obvious Stuff"



Did I get that right?