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Engine idle-1986

Electrical

Vehicle Information: Year: 1986; Engine (size, modifications): 5.0; Total Mileage: 200,000; Transmission type: Manual;

My '86 928S starts and idles correctly for about 10 seconds and then begins idling roughly, vacuum drops from 20 to 10 inches and the smoke indicates a rich fuel mixture. The factory manual suggests removing the alternator and after doing that it runs properly. Replacing the alternator with a rebuilt one, which has a rebuild performance check sheet, returned the rough idle. All the related sensors have checked to be within the manual specs. MAF and batteries have been swapped with known good ones. The idle air valve is new. Fuel pressure is proper with no leak down. Where should I look next?

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