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Alfa 164 3.0 V6 12v 1990 bad idle when hot

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Alfa 164 3.0 V6 12v 1990 bad idle when hot

Postby tom50 » Fri Apr 08, 2016 8:32 pm

Hello,

I bought an alfa 164 v6 3.0 12v, such a cool car with a wonderfull engine.

Since i bought it, I am getting a bad idle, difficulties to start it, and bad rev when under 2000 rpm, when the engine is warm. (when the engine is cold, it drives a lot better, i can drive in first gear under 2000 rpm with no shaking or risks of stalling)

I checked for vacuum leaks, and replaced 2 hoses around the evap canister which were in bad shape.

I am strongly suspecting the AFM to deliver the wrong signal to the ECU, but i don't know the right voltage it should tell.

You will find attached the parameters when the engine is idling rough.

As you can see, AFM is telling it 1,367 but it varies up to 1,600 at idle.

Lambda sensor shows between (sometimes) 90mv to 700 mv

As the engine is hot, it is in closed loop lambda mode, which is what it is supposed to be.

Did somebody ever had that kind of problem before ?

Any help will be greatly appreciated,

Thank you,
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paramsAlfa164.png
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Re: Alfa 164 3.0 V6 12v 1990 bad idle when hot

Postby tom50 » Tue Apr 19, 2016 5:34 pm

Hello,

I am answering to myself, it is the brake booster which has a small leak which leads to that problem, i tried to plug the vacuum line that runs from the plenum and the idle is better everytime i try that test.

It could also be valve deposits, the car has long crank time both hot and cold, either injectors are clogged or valve deposits could be responsible of that, i am going to use an injector cleaner which i put in the gas tank, and see if it goes better.
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Re: Alfa 164 3.0 V6 12v 1990 bad idle when hot

Postby alfa east » Wed Apr 20, 2016 2:39 pm

Thanks for doing that; always helpful for the other members here!

Planning on doing a proper intro in the relevant topic (preferably with photos of your Bella)? Welcome on the site anyway!
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Re: Alfa 164 3.0 V6 12v 1990 bad idle when hot

Postby Alfan » Sun Apr 24, 2016 7:25 pm

The engine RPM seems very low in the diagnostic photo you attached.

I just talked to a Thema 8.32 owner today. He had a problem with cold start. It turns out that the ignition part where you insert the key (can't remember the English word for it right now) had a bad connection, meaning that the fuel pump would only run shortly when turning the key to 'ignition', and not enough to create enough fuel pressure for starting. When turning the key all the way, the fuel pump would run, but it would take time for the car to start.

I know this unit have caused many different problems for owners of cars from Fiat, so it might be worth taking a further look at it and see if it is corroded. Lubricating the plug would at least be a good thing, no matter what.
1994 Alfa Romeo 164 Q4 Proteo Rosso 550.000km
1989 Lancia Thema 8.32 Verde Indy 265.000km
2001 Alfa Romeo Spider 3.0 24V Blue Lightning 55.000km
2015 Alfa Romeo 4C Rosso Competizione 85.000km
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Re: Alfa 164 3.0 V6 12v 1990 bad idle when hot

Postby wilco » Sat Apr 30, 2016 1:32 pm

I would suggest to read the lambda values with and without the brake booster. see if there is a difference in values. it shouldn't
Henry Ford, 1939: "Every time I see an Alfa Romeo pass by, I lift my hat."
--Alfa Romeo 164 3.0 V6 24V Q4--
--Alfa Romeo 164 3.0 V6 24V--
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Re: Alfa 164 3.0 V6 12v 1990 bad idle when hot

Postby tom50 » Sun Feb 12, 2017 8:44 pm

Hello,

Just a quick update to the idle problems i was having, i finally found the real cause of the problem, after searching for months and months : althought spark wires were new, they were faulty, and did not conduct electricity well (infinite resistance when reading it end to end with a multi meter on Ohms position) for the back 3 cylinders under the plenum (there was oil in the spark plug wells on the back cylinders, did it cause the wires to fry... i don't really know)

Another story to tell everybody that you should stick to the simple stuff when diagnosing engine performance problems (test your spark wires resistance :) it should read 9-10 k ohms or similar, but if infinite reading on any ohm scale they are dead)

Now the engine works fine, stopped shaking, handles <3 k rpms fine... a real pleasure to hear this engine run like the busso myth !
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Re: Alfa 164 3.0 V6 12v 1990 bad idle when hot

Postby Alfan » Mon Feb 13, 2017 9:03 am

Great and thanks for the update :)
1994 Alfa Romeo 164 Q4 Proteo Rosso 550.000km
1989 Lancia Thema 8.32 Verde Indy 265.000km
2001 Alfa Romeo Spider 3.0 24V Blue Lightning 55.000km
2015 Alfa Romeo 4C Rosso Competizione 85.000km
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