1989 Cavalier Z24 3.1 rough idle and hesitation

I would check timing or spark plugs

Is the check engine light on/flashing? You may have a cylinder misfire causing a rough idle and poor hesitation like acceleration

PROBLEM TROUBLE AREA
Rough idle, stalls or
hesitate on acceleration :
.Spark plug faulty
. High-tension cords faulty
Ignition problems:
• Ignition coil
• Igniter
• Distributor
. Incorrect ignition timing
Vacuum leaks:
. PCV valve and line.. .
. EGR line..
. Intake manifold.
• Throttle body
• ISC valve
• Brake booster line

• Throttle body
• Brake booster line
. Incorrect idle speed
. Reset timing
. Adjust valve clearance
. Check fuel system . Check air cleaner
. Incorrect valve clearance
. EFI system problems
. Low compression

yes socket on knuckle bar on crank shaft main nut were pulley is down bottom of engine turn clock wise

A number of things. Tune up, water in gas, timing, air filter, fuel filter, carb, injectors, etc.

I had the same problem on my Z28. I replaced the battery (weak) and it solved the problem.

Sensors, try the o2 loacted on the muffler, normally sensor are the number one cause for rough idles, so I heard, please rate thanx

Replace the temp sensor.

It sounds like you may have a broken exhaust valve spring, although, like you have found out problems like this can be very hard to diagnose, but anyone with a compression tester and couple other tools could find out if this is the case. Hope this gives you another idea where to look.

What happens when you unplug and cap the vacuum line at the EGR valve? Does the problem go away? Before doing this does the car idle rough? If so perhaps the EGR is stuck open...