So the harbor freight cleaner says don't use on aluminium. Did you dilute it at all or use it full strength?I recently replaced the right side Tandem Pump (I actually rebuilt it for $47) and the entire process was filled with learning that I'm now going to pass along to everyone else. The biggest learning experience was cleaning the black exhaust build up from the throttle and intake manifolds. If you try carb and choke cleaner you are going to make a big mess. If you try brushes you are going to make a big mess.
I used a gallon of "Super Heavy Duty Degreaser" from Harbor Freight and soaked the intake in my kitchen sink (I'm not married and can do this...) overnight and literally the next morning I had a solid black, oily liquid in my sink and when I drained it and rinsed the intakes they looked new, both inside and out. For $10 and no scrubbing, you can clean these to new condition.
My Touareg has 138K miles and the throttles had a half inch of gunk and the inside of the manifold probably had a quarter of an inch. The most INTERESTING, but not surprising part, was the rumble at idle when in Drive or Reverse (which there are other post about) has decreased by 75-80% from being able to breath better.