96 3.1L Rough Idle/Misfiring [Archive] - GrandAmGT.com Forum


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03-13-2012, 01:33 PM
Hey guys, I've got a 96 Grand Am GT with the 3.1L v6 in it and it seems that whenever it gets warmed up to temperature on a relatively warm day when I start it up it chugs and sputters while the RPMs fluctuate up and down. Even when I rev it up it continues. I took it for a ride around the block and it is reluctant to go and continues to misfire.

Oil and coolant are fine, fuel pressure is good, the injectors are clean, the catalytic converter is brand new, plugs and wires were done recently, fuel pump is good, and the fuel filter is new. It is not throwing any codes at all when it does this and my Dad and I are at a loss for what it could be.

I've started to think it could be the crankshaft sensor or an O2 sensor failing or something. Like I said no codes are thrown and the check engine light stays off throughout all of this every time it happens. When the engine is cool it seems to run okay but as soon as it heats up it acts up.

Any help would be appreciated. Thanks.

mohamed elsebae
03-14-2012, 03:33 AM
i had the same symptoms before in chevy malibu 3.1 l 98 model one was due to vaccum and air leak, the problem had been fixed after finding the leak. also check lower intak manifold jascket for leak.

03-15-2012, 08:33 PM
Where should I be looking for the leaks. I'm not able to find any diagrams on the vacuum lines.

mohamed elsebae
03-19-2012, 04:17 AM
there is many plastic tubes in engine bay, diameters from 4mm to 8mm all around the upper intake manifold and the engine firewall side, also map sensor, fuel pressure regulator and PCV system connections check them all.

03-20-2012, 03:29 PM
Why would those thing's act up when hot? The PCV valve is new and the FPR is fine. There is a small vacuum leak but it's negligible.

Some updates though, this occurs after the car has been turned off when hot and it sits for a short period of time. Once you try to start it after sitting for a few minutes, it starts and chugs horribly and then dies, then refuses to start.

mohamed elsebae
03-21-2012, 11:06 PM
to narrow the searching this issue related to fuel / air mixture with different reasons, uper intake manifold leak could be one of them should be no any leak there i experienced these before and i installed blind plug when i found air come out from one nozzle on most left side of upper intake manifold. ( better to check when the shacking starts ). after that if no leak found inspect the fuel system specially the fuel pump i replaced it 2 years ago.