The upper intake manifold gasket and/or a PCV vacuum lines/hoses can develop vacuum leaks with age. This type of leak can result in a higher that normal or rough idle.Google+
Car Problem Reports
Chevrolet Monte Carlo Intake Manifold and PCV Vacuum Lines/Hoses Can Leak Due to Age
Chevrolet Monte Carlo Problem
Engines Affected: 3.1L V6, 3.4L V6
Average Mileage: 148,688 mi (80,000 mi - 254,128 mi)
Visitor, 1999 Chevrolet Monte Carlo, 3.1L V6, 155,000 mi
The T at the intake valve cover breaks causing a vacuum leak. This feeds the cacuum to the pcv valve.Irratic idle and racing rpms.
The T at the intake valve cover breaks causing a vacuum leak. This feeds the vacuum to the pcv valve. Irratic idle and racing rpms up 2 or 3K. NAPA had the part in stock Positive Crankcase Ventilation Valve Tube Assembly (Part Number: NOE 7151782). Not hard to replace once motor has cooled down. Since you are replacing this part you might want to replace PCV value grommet (NOE 6301362) and PCV value (MPF 39307) everything was under $20 total.
noticed leak at hose connecting to pcv valve and tried repair w silicone no help. read about egr issues on this engine so I disconnected the egr solenoid and drove that way for a while. burned lots of gas and no help so I reconnected the coupler. Low and behold the trouble light went out for a while but came back Then found a leak of the hose into the purge valve and when I repaired it light went out for a while, now back with a vengeance after I used a vinyl tubing. Bottom line is I think that vacuum is the culprit but the computer is aggravating the issue.
Idles so low cant get enough power to get on expressway. Idles so high the rpms went from 2 to 3 without touching gas. worst car i ever owned.
Visitor, 2000 Chevrolet Monte Carlo, 3.4L V6, 137,000 mi
My car would act like it was going to stall.