Why does your Chevy Celebrity miss and do it even worse when the speedometer starts working?
That sounds like a problem within the engine control module or possibly the wiring,
The 1987 Chevy Celebrity uses an electronic speedometer, there is no speedometer cable. Assuming your speedometer has failed here are some possible causes: The VSS. vehicle speed sensor, may have failed. The speedometer may have failed. The ECM, engine control module aka computer, may have failed. There may be wiring issues such as unplugged, dirty connections, broken wires, etc.
You didn't tell us quite enough information. Top speed depends quite a bit on which engine and transmission your car has as well as how well the engine runs. The speedometer in these cars only goes to 85 MPH, but a good running car will easily run faster than that. We have a 1986 Chevy Celebrity with the 2.8L V6 and automatic overdrive transaxle and a very rare cop car speedometer which goes to 120…