those engines are known for intake vacum leaks and water leaks. spray water around the intake area next to the valve covers and forunt and back of the engine if the engine speeds up there is a vaccum leak. if there is no change check the egr valve
In most installations, vacuum to the EGR valve is controlled by a Thermal Vacuum Switch (TVS); the switch, which is installed into the engine block, shuts off vacuum to the EGR valve until the engine is hot. This prevents the stalling and bumpy idle which would result if EGR occurred when the engine was cold.
On 1979 and later models have a ported signal vacuum EGR valve. The valve opening is controlled by the amount of vacuum obtained from a ported vacuum source on the carburetor and the amount of backpressure in the exhaust system.

To test the EGR valve operation, place a mirror under the valve to see if the valve moves when the throttle is opened. If the diaphragm does not move, there is either a problem with vacuum or the valve is stuck. With the valve stuck open, the engine will run very rough at idle or may not even start. If it is stuck closed, you would likely experience severe pinging when the engine is under load or on acceleration. With a vacuum gauge hooked up at the EGR vacuum line, you should see vacuum on the gauge when the throttle is opened. To find out if the exhaust gas is actually recirculating, use a hand vacuum pump to open the EGR valve with the engine idling. If the engine runs rough or stalls, the exhaust gas is recirculating. If it does not, remove the EGR valve and clean it, as well as the EGR ports in the intake manifold. When testing with a hand vacuum pump, EGR valves should hold a steady vacuum and not leak. Apply vacuum to vacuum port. The valve should be fully open at 10.5 in. Hg (72 kPa) and closed below 6 in. Hg (41 kPa) on 1984 and earlier models. On 1985 models, the valve should be wide open at 21 in. Hg (144 kPa) and closed below 6 in. Hg. (41 kPa) If the valve does leak, it must be replaced.