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Joined: Sat Aug 19, 2006 12:07 pm
Location: Ytterby, Sweden

Re: Idle Irregularities

Post by Brian16 »

Hi Romeo,
WOW, You have been busy changing hardware. If you have'nt already done so You and Mel could try the following
1. With the cold start injector disconnected start the engine cold and allow it to warm up at idle. If the problem of falling engine speed and rough running is now worse, then the CSI is probably OK.
2 Repeat #1 this time with the CSI connected and disconnect the aux air valve. Open the throttle a bit to compensate for loss of aux air and allow the engine to warm up at idle. If the idle quality is now better then the aux air could be the problem.
3. Start the engine cold ( everything connected) and allow to warm up at idle monitoring the ignition advance using a strobe lamp. Does the ignition change much when the engine speed changes ( or just before it changes)? If so the problem is ignition related.

Romeo: I don't hold out much hope in changing the ECU. If you have easy access to a spare one then by all means, but typically the ECU either works as it should or it does'nt.

Good Luck,
La vita e troppo breve da non guidare un'Alfa
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Posts: 32
Joined: Tue Mar 01, 2005 3:37 pm
Location: Melbourne Australia

Re: Idle Irregularities

Post by Al_Cam »

A couple of other suggestions.

Australian models (and Switzerland according to the manual) have an excess vacuum valve on the plenum chamber - 2 hoses to the plenum, one to the air intake tube. I had an idle that would get a little higher (200-300 rpm) when fully warmed up. Seemed to drop or rise at random. Tried just about everything then disconnected that valve from the air intake and plugged the pipes. I guess it was all clogged up with oil after 27 years. Not worried about emissions as it burns heaps of oil.

I also thought that the AAV was closing too quickly as the idle would drop to stumbling about 1 minute after starting. I tried disconnecting the heater plug to the AAV but it would idle way too high after about 30 seconds. I ended up putting a 12 ohm 10 watt resistor in line with the AAV heater and it idles nicely now. Haven't tried it in summer yet though.
Al Campbell
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Re: Idle Irregularities

Post by mjr »

after having done all of that and not found it, its time yoiu got it plugged into and exhaust gas analyser through the start up and warm up, so that you can see what is going on. i bet she is running way rich or way lean during this condition. with the injectors you had cleaned, did you get flow values back on them?
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Joined: Tue Nov 30, 2004 3:50 pm
Location: Ellicott City, MD

Re: Idle Irregularities

Post by shures »

This thread has been dormant for a long time and seems unresolved. I like how it started: "just asking if anyone has had a similar problem and can share their solution" or something similar. I may ask some questions too at the start of a problem like this but really believe the answer comes from careful trouble shooting.

I have a question about the idle speed adjustment. I changed the o ring in mine recently. Before I did it and after I did it the brass nipple the hose from the main air intake attaches to was loose. If I tighten the lock nut enough to really hold that nipple the idle drops a lot. I know I can adjust the throttle plate open and reset the TPS and get the idle back but have not gone through that. Instead I backed the adjustment out to where I have a good idle (900 RPM I think) and left it loose.

Here is the rub. I did have an vacuum leak which turned out to be a loose clamp on a plenum coupler. Of course I suspected the loose nipple first but I could not detect a leak with propane (I use a hose from an old torch), carb cleaner or my stethiscope.

So the question: is the brass nipple on your idle adjustment loose also? And the corollary question: should I tighten it, readjust the throttle and TPS?

AND one more thing. To solve the original idle issue in this post I recommend going through Greg Gordon's Tune Up page. Each of us has a view on this but nothing beats hands on trouble shooting. I didn't read much about grounds. But I do pay a lot of attention to grounds on fuel injected cars. So my 2 cents is check those grounds, especially the bundle at the AAV and the one near the front of the plenum on the left side.

Scott Shure
Ellicott City, Md
85 GTV-6
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