Hi everybody,
new here looking for some help. Just got my 93 z28 running down the road couple of weeks ago. Its a 6spd with 3:73 rear gears. Problem im having is the engine idle stays at about 1500 / 2000 rpm till I bring the car to a complete stop. When I first start it it idles at about 1000 rpm till I start moving then it stays high. I have no idea what has been done to the ecm if anything. The engine is a 355 with a good size comp cam and 36# injectors. I guess my main question is, will the speedo being off by 10miles per hour cause the idle to stay up if the car is moving?
thanks for your help

1st time out of the shop

 

There is a sensor in back of the transmission that tells the the ECM how fast the output shaft is turning. The ECM knows the tire size and the rear end ratio. Idle has no effect on speed. You came with 3:23 rear so if you have 3:73 you ECM would need updated to get the speed right.

 

thanks for the reply but I think you missed the question. What my problem is ; after driving and pulling up to a stop, the engine stays at 1500 to 2000 rpm until I come to a full stop. It then will idle at 900 to 1000. With the speedo unhooked it returns to idle as soon as I let off the throttle no matter the car speed. Any guesses?