Weak starter / battery symptoms, but it's neither
 

Ok guys... So I got the new motor in the car, got it inspected and emissions waivered. Sometimes (almost always) when I start the car, the motor will crank really really slow, almost to the point of flooding itself. The battery and starter are relatively new (month or two on each). When I flip the fuel cut switch to off however, it will crank at normal speed. Now it's not really a problem to have to keep doing that (Start with fuel off, and flip the switch when it catches), But it's not right. I just started having the problem recently. My plan is to run new wires to the starter and see if that works. But I was just wondering if it could be anything else.

88 S4, pretty much stock except for cold air and sub zero block-off. The injectors were cleaned and tested when I put the new motor in.

sometimes new starter can be bad.
but first, as you said you should check the wiring, might be corroded. Check the engine ground and the power cable going to the starter.

I had the same problem as you, it turns out for me my starter was going bad. It would crank slow and 3-5 seconds later it starts cranking faster. Sometimes the field winding assembly corrodes from water, or they just arent good enough to rotate the armature to turn the engine over.

Edit
Forgot to mentioned that you should also do a voltage drop test.

you can also try a thinner viscosity oil.That will help on colder Days.I run 10w30 Up here in Canoe country..NO ill effects.The car hasn't had problems(where's the Wood?..Touch!) in three years.I am going to switch to 20w50,as I don't think that viscosity will harm it either..I does sound a little weak though,If Just Getting the Fuel pump to kick on will make the car crank Slower.I would be checking some connections and clean them up a bit though..(Btw,Personally I am against a Fuel Cut switch..it in my opinion is an Easy way to get out Of Properly Fixing the Flooding on these cars.Maintenance is Number one.Not Ho-Hum..I''ll do it tomorrow)..sorry to,Rant..Cheers,STYX.

I'm running 10W30 too. It's been in the 80's for a long time now. What connections do you recommend specifically?

It's not something with the fuel pump. I just went and tried to start it with the switch off, and it still cranked slowly. For the hell of it I'm gonna get my battery and alternator tested.

Check all connections: battery terminals, and starter terminals. Mine wouldn't start the other day and when I looked inside the + battery terminal it was green and full of corrosion. I cleaned it off, put on a new terminal, and I was good to go.