AAV Question

[RRoller123]

I have read here on the forum that the AAV should either completely closed, or have a small gap when warmed. (mine has the small triangular gap when warmed). Anyone know for sure which it is supposed to be? Fully closed or partially open? I ask because I have an FI idle problem, whereby the engine idles poorly when cold, better but still somewhat poorly when warm, and the distinguishing feature is that when I decelerate and stop at a red light, the engine rpms dips very low and then slowly comes back up over a few seconds, and there is some idle misfiring. The engine runs beautifully at all other speeds, no misfire, has great power, 145-150 compression, and I have been through all the possible vacuum leaks (with a propane torch too), checked the Thermo Time Switch and the CSI, had the injectors serviced, timed the engine with a light, new plugs, wires, main air tube, tested the main temp sensor, and probably a few other things I can't remember.

So I am down to thinking the AAV is bad, or the AFM has a bad spot around idle, or could the O2 sensor cause this? I have no idea how old it is.

Possible low fuel pressure from the regulator? But wouldn't that effect performance across the range?

I am at my wit's end and don't like to just change parts, but I am going to start doing so shortly if I can't get a feel for which way to go on this.

Thanks!

Pete

[wizard124]

Try pinching off the AAV air line. Does the idle steady out? If it does then try adjusting the AAV fully closed warm with that little nut.

I read that the O2 sensor needs.to be hot for it to give a signal. At steady idle, it is probably not hot enough to change the ECU output.

[vandor]

If it idles at the proper RPM, but poorly when warm, then it's not the AAV. It ONLY controls idle speed. It cannot create a poor idle condition, except that if it malfunctions the idle speed may be so low that it appears that the engine is idling too slowly.

Have you adjusted the idle mixture with the screw on the AFM?

[So Cal Mark]

the opening should be larger when cold, it allows air to bypass the throttle, raising the idle speed

[RRoller123]

Thanks, all, I will try all the suggestions.

For the AFM adjustment, don't I need some kind of metering to know when it is set correctly?

I wasn't aware that the AAV could be adjusted by the nut. I will set it so it is fully closed when at full temp.

Pete

[RRoller123]

One more question:

I have properly set the throttle position switch, but I was wondering: Does this give a variable position signal through the throttle plate movement range? Or is it just binary, open at idle, closed when the throttle plate is open? If it is variable, I have no specs on how to test it.

Thanks.

Pete

[focodave]

You may try this article for help:
http://www.hiperformancestore.com/Ljetronic.htm
You need to read it thoroughly and carefully, as it is written for a number of different cars that use the L-Jetronic system.
There is a section that describes how to test and set the TPS properly.

Here is what is inside the TPS:
http://www.mirafiori.com/~thad/fi/


It is binary, as it contains simple contact point switches.

[RRoller123]

Thanks, focodave, that is exactly what I was looing for. I now won't fiddle with it as it is not broke.

[RRoller123]

Well it is not the AAV.

There is voltage to the AAV when ever the ignition is on (on my 80FI, is this normal across all FI cars?), so I just unbolted it so I could see through, turned on the ignition without having to start the car, and watched the opening slowly close. It was wide open when it started, and it took about 4-5 minutes and it basically closed almost completely. I fiddled with the nut and got it to completely close.

So I am left with thinking there is a bad spot at idle in the AFM. One more time, pull the cover and see if I can move the arm to fresh TFM material. Not too many other things that I haven't touched that could be causing this poor idle.

Pete

[focodave]

One more question:

I have properly set the throttle position switch, but I was wondering: Does this give a variable position signal through the throttle plate movement range? Or is it just binary, open at idle, closed when the throttle plate is open? If it is variable, I have no specs on how to test it.

Thanks.

Pete

Should be closed at idle -- not open.
Test between terminals 2 and 18.
If there is no continuity (open circuit) when the throttle is closed, you need to adjust the TPS so that there is a closed circuit between terminals 2 and 18. This signals the ECU to enrich the fuel mixture by lengthening the on-time of the injectors at idle.

[vandor]

>For the AFM adjustment, don't I need some kind of metering to know when it is set correctly?

I theory. In practice, you can just set it for best/highest idle speed. If incorrect, it can cause very poor idle.

BTW, have you checked that the oxygen sensor is working properly (voltage changes constantly between 0.1 and 0.9 volts when warmed up). If not, it may be giving a wrong signal to the ECU, which in turn may richen or lean the mixture based on false info.

[RRoller123]

Thanks Csaba, I will check those ideas out tomorrow. The car runs amazingly well, except at idle. Driving me crazy.

Pete

[RRoller123]

The O2 sensor seems fine, averages around 0.4, jumps from 0.1 to 0.8 or so. Found the connection a little loose, tightened the female Faston type connector and the car is now running a little better. It's always the little things.....

Fiddled with the AFM and running better still. Getting near the end of this idle problem I think.

[76was124]

The O2 sensor seems fine, averages around 0.4, jumps from 0.1 to 0.8 or so. Found the connection a little loose, tightened the female Faston type connector and the car is now running a little better. It's always the little things.....

Fiddled with the AFM and running better still. Getting near the end of this idle problem I think.

Did you resolve your idle issue? I had the same problem...makes for fancy footwork to prevent a stall during a fast decel (for a yellow to fast red light type stop). Slight dip to around 250RPM or so, then right back up. I had adjusted the throttle stop and Tps which fixed it, but now a month later it's back again because I was tweaking the aav, throttle stop and idle screw. I think I need to cheat on the TPS position a little to have it kick in a tad earlier, as I suspect the throttle plate return might be a little slow (weak spring with high airflow?) during the rapid decel, and not quite fully closing immediately and tripping the TPS.

[RRoller123]

Good idea, I haven't fully resolved it, but I did think I heard some slight hissing around the idle set screw, and there is an O-ring in there that apparently none of the vendors sell, (why I have absolutely no idea) so I plan to head off to the auto pahts mega store and see if I can find a suitable one so I am sure is sealing the thing properly.

I also took the temporary measure of increasing the throttle plate set point to artificially raise the idle, then shut down the idle screw completely, and it runs a little better this way, but just for now. I am going to solve this damned problem if it kills me. I have been through every single sensor, wire, possible vacuum leak etc. I now fully understand why people take this GD FI system off and put carbs back on. Majicwrench would be very happy with me, I have been testing every GD thing I can get my hands on to find the source of this problem, and it is not going to beat me. I am going to win eventually. It is getting personal now.

Also possible that regulated fuel pressure is too low, so ordered a gauge from Summit and will install that and see what's up. It is possible that it may take a few moments for the pressure to recover after high revving a downshift coming up to a light and then letting the idle drop. Will also clean and check the terminal voltage at the fuel pump to make sure it is getting enough VDC.

I suspect the AFM flap may have been f-ed with by a PO and that the spring tension is too light, allowing the arm to flutter when one suddenly decelerates, and that would likely cause this problem. There was a youtube video on this somewhere. So the top will come off the AFM and I will take a look at how it is behaving and make a judgement on that.

Last drastic step (because it is an unbelievable PITA on these cars) is to remove the intake manifold and reset the injectors with new seals, and add a new gasket. It is possible that there is a leak somewhere there, although it is not obvious.

Good luck, keep posting, there is a solution somewhere. I don't like to just go and replace parts, but I am sorely tempted to put a refurbed AFM on this thing and see if that does it.

Pete