Ok here are some things to check. You will find a small vacuum line running from the back of the engine to a small rubber "Y" connection just in front of the fuse box. It is usually strapped to the large black vacuum line going to the brake booster. One of the connections goes to a yellow vacuum check valve that has 3 connections on it. One of these connections (on the Y connector) goes to the line leading to the economy guage. Check these vacuum circuits carefully. I have seen the Y connector get hard, start leaking and generally fail. This would cause a vacuum leak and affect the mixture of the engine. Also check the vacuum connection on the back side of the engine for leaks or broken parts.

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k