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So I'm trying to get to the bottom of my bucking and sputtering issue.

I printed out Eric's L-Jet diagnostic to try to narrow those items off the list of potential suspects. Test #1 was for false air. As instructed I removed oil filler cap with engine running and see if idle changes. It did not. I assumed I had false air somewhere and began checking/replacing every single hose and connection.

When checking for false air at the idle adjustment bolt I thought I'd check to make sure the washer was still intact. I removed the bolt and found it was still there and in good shape.

Idle had always been in the neighborhood of 1300-1500 on the dash tachometer since I purchased it and started refreshing. I chalked that up to the notorious inaccuracy of Alfa Romeo gauges!

For grins, I set idle to 1000 on the dash gauge and started her up. She idled a great deal lower than before.

When I removed oil filler cap idle lowered greatly and nearly stalled.

Am I to assume that I do not have a false air issue since idle now noticeably changes when I remove oil filler cap??

The bad news is that she still sputters and stalls intermittently at operating temp.:cursing::cursing:

Has anyone had any experience with a very high idle giving a "false positive" for false air??

Thanks in advance-M5
 

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miami592,

I have had a lot of trouble with random air leaks in the large, main air duct and one of these days will buy a replacement. Over many years, they can develop cracks, which often only present when you are accelerating and your (perhaps) sketchy engine mounts allow the engine to rotate and allow "false air" to bypass the airflow flapper and mess up the mixture.

I would remove the duct and use a strong lamp to check around the flex sections. The mounting ears may also develop cracks. While spraying the plumbing with brake cleaner (no residue) might help identify an air leak, at idle the crack may not be large enough to show any change in rpm.

Oh, and please fill out your signature. ��

All the best.
 

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Has anyone had any experience with a very high idle giving a "false positive" for false air??
This is a know issue with L-Jetronic. I have had problems with it on the V6 cars as well.

Let me describe WHY it happens. If the L-Jetronic sees above 1,300 rpm while the Throttle Position Switch (TPS) is on the idle setting then it cuts fuel. The engine then begins to stall and the idle falls below the 1,300 rpm limit and fueling is restored, so the engine surges back to life.

This appears like a very hard, fast "hunting" idle which can usually be traced to a false air leak. However in this case re-setting the high idle and properly calibrating the TPS (should click off the idle setting with just a few degrees of movement in the throttle bell crank) will cure the problem.
 
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