i have a 99 tahoe with about 135k milesit keeps on sending multiple misfires code, i replaced cap,rotor,wires,plugs are not to old maybe about 4 months and alsohad a top end fuel system claened , error code says fuel/air mixture multiple cylinder misfire, its running real lean you can smell the gas on the exhuast, sometimes it is hard to start it takes a couple of seconds and sometimes starts right up ,its loving gas like crazy []need help if anyone has had this problem???

 

Are you looking at the codes? Does any one cylinder show more than others? Have you done a compression test?

I had what sounds like a similar issue on my '96 Tahoe. I monitored the codes and it kept showing multiple misfires and cylinder #8 would keep showing up. We did all the usual stuff (checked fuel/spark at my nephew's garage) then ran a compression test. Turned out oneof the valve return springs (on cyl 8) was broken. Luckily it didn't do any damage to the valve according to the leak down test.

Funny thing, this was on a new Jasper engine with about 2K miles.

 

If you are smelling gas at the exhaust then it is running rich.

Most commonly these symptoms are the result of a faulty intake manifold gasket.

 

I'll check it out i talked to a mechanic he also said it might be the fuel pressure regulator. that it might be bad cause it regulates the fuel mixture dont know if true but hopefully someone might have the same problem.

 

Run a drive cycle, check ur codes, multiple means multiple, look coil pack, ignition control on the side of the throttle body, fuel filter the right plugs, multiples r real common on imports with different from stock plugs... rich codes can be 02s n cats too