MPG gauge causes my e30 to deacelerate weird issue help

[josianjehu]

okay i have an early model 325es from 1987 now the issues came back again because it stopped happening a while ago so recently i replaced my tps after installation everything was tip top great no problems there now after i had ruptured a break line and fixed it after i turned on my car it was idling low and also whenever i quickly revved up my engine and let go it would go to around 500 rpms and then up to normal now heres the weird part when im driving and im pressing the accelerator the car works fine it reads 0mpg like it has always done but when i depress the accelerator the car reads max mpgs and the car sounds like its whirring down when i let off the clutch while its whirring down the rpms drop to 500 rpms and then to normal i need to know what feeds the mpg information because i know for a fact that the issue is mpg sensor related something that feeds the mpg is wrong. Could it be a bad battery? i had gotten my battery recharged because it was going bad. but besides all that any help or tips would be amazing thanks

[superj]

it could be the battery in your gage cluster.