Vehicles using the enhanced vortec V6 engine may be hard to start run poorly and/or use to much fuel due to a fuel leak inside the intake manifold plenum. Commonly this is caused by a leaking fuel pressure regulator or fuel line. The fuel system will need to be pressurized with the upper intake manifold removed in order to determine the exact cause of the leak. Removing the "tuning valve" from the upper intake can allow for limited visual inspection without removing the upper intake manifold.Google+
Car Problem Reports
GMC Jimmy Engine Running Rich Due to Fuel Leak Inside Intake Manifold
GMC Jimmy Problem
Average Mileage: 139,000 mi (80,000 mi - 200,000 mi)
Visitor, 1994 GMC Jimmy, 80,000 mi
gas in oil, failed emissions test
I think I have the same issue, waiting to check with a fuel pressure guage
Engine started having rough cold starts and fuel pump could be heard running constantly. Computer started throwing misfire and rich fuel codes. Checked pressure and found that it fell off rapidly with key turned to off.
Hour and a half spent under my carport replacing the regulator and it's all fine now.