The purpose of the EHA is to adjust the mixture of the engine and keep it at the lambda point. Lambda is where the air fuel mixture is at its optimum point. There are a lot of variables that cause the engine not to operate at this point so the oxygen sensor is the device that measures the oxygen content of the exhaust gases and the engine managenment systems adjust the air/fuel mixture to keep it at lambda. The EHA has a limited authority as to how far it can affect the air fuel mixture. So if the engine basic adjustments for air fuel mixture is too far off or there is some other problem the EHA cannot compensate. You should first disconnect the EHA and perform all the basic adjustments to be sure that the engine is as close as possible to being perfectly set without the lambda system operating. Then connect the EHA and that will insure that the EHA has as much authority as possible to keep your engine at the optimum operating mixture ratio.
In theory disconnecting the EHA should not change the engine operating characteristics . The fact that it does indicates that it is having to work to keep your engine in lambda and I would conclude that your engine needs to be adjusted. When the EHA is connected a closed loop control system is now adjusting the air fuel mixture and will compensate for any adjustments that are not correct. Also the fact that the valve is leaking fuel would indicate that it needs to be replaced.
I hope I have not confused anybody. My explanation of the lambda system is an attempt to help provide an understanding of what is really going on with the EHA and is purpose in life.
Any car that has an oxygen sensor is using this basic closed loop system to maintain the air/fuel ratio. Different injection systems have different methods if controlling the fuel delivery. But the principal is the same in all cases. In your case the EHA is the device that changes the air/fuel ratio.
Before you start the shotgun approach and start replacing parts, I would do the basic adjustments and go from there. Look at the on-off ratio and that will tell you a lot about the mixture settings.
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