Rough Idle 1998 Chevy Cavalier What could be the problem?

1. Do you mean it runs rough after starting ? Check spark plug wires.. Dist cap. Spark plugs.. Look for Vacuum Leaks..

run fault codes to find the faulty sensors

http://realfixesrealfast.com/realfixesrealfast.com/Diagnostics/Pages/Stall_at_idle.html

This may be your problem

if it is a 2,4 dual over cam enginge it is the coil pack shorting out and it needs replaced

FIND BG PRODUCTS DEALER AND GET TOP CLEAN.MAY BE AIC MOTOR. USE BG 44K TWICE A YEAR IN FUEL TANK

need to pull codes from computer see if it throwing any codes out

Sounds like a 2.4 Quad four engine? If so the chain has either different colored links marked links that have to be aligned with the marks on the cam gear[s] and the crank gear.A chiltons book will show you how.

Check for vacuum leaks. Spray some carb cleaner or WD40 around the intake manifold, trottle body and any vacuum lines. Check for loose connections on engine wiring harness (Maybe you disconnected a sensor, and forgot to re-attach it?).

Have you made sure your getting spark on every cylinder from the coil pack?

vaccum leak