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Discussion Starter #1
Buon giorno tutti, come sta?

I had a little success amid failure this morning and want to ask how to troubleshoot an '82 GTV6 with an apparent "too rich" idle when COLD. What parts or systems compensate for temperature on an '82? Does the ECU control cold-start mixture? Does it involve more than the AFM adjustment (I'm aware of the gross adjustment at the internal spring mechanism, as well as the AFM fine mixture adjustment screw under the metal plug). I see there is a throttle-position screw on a lever at the intake plenum, but I'm uncertain how or if, that acts in concert with AFM and mixture screw.

I did a quick search here on the Forum, Fuel & Injection Forum, but didn't find direct information on Cold idle mixture.

HISTORY:
This GTV6 has had a unstable idle when cold. Warm is never a problem, though it does "hunt" a little. When cold, it starts fine, then the idle "cycles" up and down the rpms, roughly 300rpm to 900rpm and back down, eventually it will stall. IT behaves this way until warm. I can nurse it with the throttle pedal, but I'm usually busy walking around closing garage, getting things settled before a drive, so the GTV6 sits and struggles as I walk around, then it usually stalls out. The low rpms also results in idle neutral roll over noise from the transmission. I have not been able to adjust settings to stabilize the cold idle rpms.

TODAY:
This morning at the storage garage, cold temperatures, same thing on start up, and it stalled several times. It became harder to start, and eventually just didn't start at all, just cranking. A sniff test revealed the exhaust smelled really rich, which might not be unusual. I disconnected the main rubber intake trunk between AFM and Plenum and found lots of fuel puddling at the AFM and the main butterfly valve. So my diagnosis is "too rich when cold".

SUCCESS: I left the air trunk off the AFM and Plenum, got in the car, pressed WOT while cranking, and she started up after some 20 seconds cranking, then stayed running for a solid 15-20 seconds. That cleared out all the excess fuel, so I re-connected the air trunk to AFM and Plenum, and she started up fine. Still cold, still cycling the rpms, but I was in the car and kept it running with throttle and I drove some 5 miles home until she warmed up and idle stabilized.

Grazie,
- Art
 

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1986 Alfa Romeo GTV6
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The strong gas smell, in that case is normal. Gas was not being burned. All stalling cars will smell like that.
No expert here nut that sounds like a fuel/ignition problem. My gtv6 starts perfectly when cold. After start one 3k rpm gas to hold it and we are good for the day. My problems start when starting hot. it takes a really long time and you always have to be carefull with the back fires. you don;t want your plenum breaking the tea tray and going through the air.
Gas lines and coils come to mind.
 

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Not 100% sure but I believe cranking with throttle fully open triggers a 'flooded start' sequence (injectors don't squirt).

The cold start system is not under computer control - it is 'stand alone'. The Thermo Time Switch (TTS) is supposed to switch on the Cold Start Injector for a very short time (a few seconds when cold) and not at all when warm. The Aux Air Valve (AAV) is supposed to open to provide additional air around the throttle plate to raise the cold idle speed. The AAV then closes as the engine warms up to bring the idle speed back to normal. As they age the AAV gets lazy and eventually stops working. I fit a manual AAV. It is self-closing (you have to close it yourself) but 100% reliable.

The Throttle Position Switch (TPS) should be adjusted to provide a signal to the computer that the throttle is at the idle position. The computer then follows its idle map and ignore the input from the O2 sensor. If the TPS is misadjusted the computer might not know the throttle is at idle and keep trying to use the inputs from the O2 sensor to adjust the mixture - thus the hunting idle speed.

Click on the link in my signature to a page of info about the L-jetronic system in our cars.
 

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Not 100% sure but I believe cranking with throttle fully open triggers a 'flooded start' sequence (injectors don't squirt).
I too believe that is correct and I agree completely with Eric's advice.
 

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The Throttle Position Switch (TPS) should be adjusted to provide a signal to the computer that the throttle is at the idle position. The computer then follows its idle map and ignore the input from the O2 sensor. If the TPS is misadjusted the computer might not know the throttle is at idle and keep trying to use the inputs from the O2 sensor to adjust the mixture - thus the hunting idle speed.
The early GTV6 only has a full-load contact throttle switch, which tells the ECU to enter "open loop" and ignore the input from the O2 sensor. The same effect as physically disconnecting the O2 sensor.

The later GTV6 has a throttle switch with an additional idle contact, but all this does is shut off the fuel injectors during closed-throttle deceleration to reduce hydrocarbon emissions. The GTV6 has no idle control system so the "idle" switch doesn't do anything when the engine is actually idling, no extra "idle" map, just reads from the lower load portion of the overall map. Later Motronic cars like the 164 have an idle control valve, so the same idle contact switch activates the idle control system.

Also, the early, unheated single wire oxygen sensor takes a couple of minutes to fully warm up and have an effect on the fuel mixture, so it has zero influence on cold start mixture. Even the later 3-wire heated sensors take almost a minute to do anything.

But, I agree with Eric that your problem might be the auxiliary air valve being stuck closed. The extra-rich fuel mixture required for cold start requires extra air!
 

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Besides the good advise above, I would take out the air duct between the AFM and the engine and have a look for cracks. I had a very similar problem and there was a 3" crack in the accordion section.
 

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Discussion Starter #7 (Edited)
Thanks guys, thank you for the clear advice and list of items to check.

It might be something I'll live with as I gather more data. I'm a little proud that I got it started by visualizing what needed to be done to clear the excess fuel, I held WOT while cranking to give it the extra air it needed to ignite the rich mixture. And it naturally didn't stay running long with all that air flowing in.

Since this is not my first stab at the unstable cold idle, - the rubber air intake is brand new, the AAV was checked and the bimetal spring looked functional last year, the single wire O2 sensor is new.

I'll see what I can achieve checking the TPS first and increasing base idle speed. Then check what I can achieve with the AFM and fine mixture screw when cold. I spent a lot of time adjusting AFM and fine mixture last year for max power at WOT.. I'll review my notes from then and see what to try after that.

Molto grazie,
- Art
 

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Discussion Starter #9
If your rubber air intake is brand new, have a look and see if the three ports are sealed off with moulding flash into the main air path.
I know what molding flash is, the extra material that seeps out between the mold's halves, right? So I think what you means is - if there is flash, it could be preventing a complete seal at the ports? I'll check.
- Art
 

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Hi there, I just had an issue with a brand new intake hose where the three aux ports had no air path to the main duct, because of moulding flash. See this post.
It's hard to see in the picture, but there is no opening in the elbow for that particular port. It was weird and caused me strife.
 

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I know what molding flash is, the extra material that seeps out between the mold's halves, right? So I think what you means is - if there is flash, it could be preventing a complete seal at the ports? I'll check.
- Art
I think he means molding flash blocking off the port in the intake boot that connects to the inlet of the AAV, which would block the extra airflow.
 
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