1994 Buick Skylark, 138,000 mi.,V-6, auto trans. Car won't engage in gear until engine is warm. Engine must run 4-8 minutes until shifting successfully. Shift lever can be moved to all gears, but transmission doesn't actually engage until engine is warm. Once transmission engages there are no problems driving. If I shut engine off, then restart, transmission will engage as long as engine has not cooled down. I checked fluid level with engine idling and warm and levels were okay. Problem has been occurring last 10,000 miles with required warm-up getting progressively longer.

One thing ive warned my friends to never do and that is to never have your trans flushed cause you may have new fluids but what about the trans filter its old and iots there for that reason to keep dirt and metal; shavings from the bands so try having your oil and filter in the transmission replaced , pull your trans dip stick and on a white piece of paper put a drop of trans oil that you have in your trans at that very moment it should be redish pink but if its brown and smells really bad then the problem is in the oil and filter . change it before u have to replace the whole trans

Is this a 2.8 or 3.1? I'm assuming so. A friend of mine has a Z-34 lumina w/ a 3.4DOHC. Same engine family; same transmission. His trans. went out before we caught the problem- it was his intake manifold gaskets, which are commonly problematic with all engines in that group. w/out sufficient vacuum, the trans. will not hold the gear strong enough and will slip until the clutches are gone. The engine is in open loop until warmed up- then closed loop, and its possible the vacuum for the trans. is related to that. Check for vacuum leaks too!

You need to change out the tranny fluid completly and change out the filter as well. The pump in the tranny seems weak and the fluid may be getting dirty and heavier and harder to pump.