Engine Issue, 99 Suburban

Yesterday the truck was running fine till we went into the store. When we came out and started her up to leave the engine ran really rough and seemed like it wanted to stall/miss/backfire when the accelerator was pushed. I decided to drive her home and it was like the engine didn't have much power.

My niece (who lives with us) asked her boy friend who works on cars some and he said it sounded like a bad PCV valve. I researched that and it sounded like what was going on with our truck. I just replaced the PCV valve and the engine is still running as stated previous. I did notice that there sounded like a hissing noise while running. Could a vacuum leak be the problem?

I will say this... up to the time of the issue there was a tapping sound that would occur under acceleration. It sounded like the tach or speedo cable was tapping. I know they sound like that when they are going bad. But now there is no tapping like before.

Please help! :frown:

Thanks
Jay