Rough and/or High Idle Due to Engine Vacuum Leak on Chevrolet Monte Carlo

Problem Description and Possible Solution

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.

Problem Data
RepairPal Verified
Average mileage: 155,947 (80,000–254,128)
Engines affected: 3.1L V6, 3.4L V6, 3.8L V6
6 model years affected: 1995, 1996, 1997, 1999, more2000, 2002
12 people reported this problem
Viewing 1 - 5 of 5 comments
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.
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.
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.
My car would act like it was going to stall.
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.