I have a 1999 pontiac grandprix with 160k miles and a 3.8L engine that shakes and makes a ticking noise only during warm up. I have always done its oil changes on time using high performance oil "ROYAL PURPLE". I have no idea what it might be since I dont get any codes.
First off royal purple while very good is way overkill for that engine, it's a waste of money for that car and going cheaper on the oil will make no difference on the engine at all. It's good for a high performance motor where there if lots of heat. The only oils I absolutely refuse to use are Esso synthetics and Amsoil as I've seen what they do to diesels vs other makes.
The GM 3.4 and 3.8 do get a bit of piston slap on start up but the shaking tells me that there is not proper combustion going on. Have you tried changing the spark plugs because I think with that engine it is every 60k miles to do them. If not there is a chance there is a crack in a vacuum hose or a problem with the throttle body.
The GM 3.4 and 3.8 do get a bit of piston slap on start up
Two totally different engines . unless you mean the 3.3l .
i would first check your plugs and wires like wip99gt said . If that doesn't resolve the shake try taking a spray bottle and spray around the intake and throttle body with the engine running if it hesitates you might have a vacuum leak . also those cars are notorious for the intake gaskets and valve cover gaskets leaking . the ticking noise are usually a lifter , rocker or piston slap like wip said . I wouldn't be worried about it. Now if you start hearing a knocking sound than u need to get worried . Have u ever gotten a random misfire code .
No I meant the 3.4 and 3.8, they're different engines but both have that same problem.
Speaking of the misfire code, which is a good idea as well, moisture in a connector can do that. I had a CTS that got moisture in the harness going to the drivers side bank ignition coils causing 2,4,and 6 misfires. It was pretty constant until I found the problem though.
Its time to replace your intake manifold gaskets i'd bet. For the 3800 they make the lower intake gasket with an aluminum frame so it should be the last time you need to do them. You might want to replace the whole upper intake manifold also. Theres two coolant ports that go up thru to the throttle body with the erg tube coming thru right in the middle and over the years the heat eats at the plastic and coolant starts leaking into the intake. If you've got the gxp then all you need is the lower's.