I'm sooooo close, but so far...

[lovinthedeez]

So I finally tore into the jetta to see why this thing wouldn't run or even start.  pulled the head, and found a nice little crack under the #2 prechamber.  #2 was firing fine before, so I slapped on a headgasket and tried my luck.  Now, it will fire right up, but the idle is up and down, just like a vacuum leak on a gasser.  I swapped in a "what I thought was good" injector, before I did the headgasket which still couldn't get it to start.    Now it starts up fine, and seems to run great when revved.  Try to drive it, and it can barely get out of its own way.  Timing is dead on at 1.00, no smoke really, but no power.  mismatched injectors maybe? 
 

[8v-of-fury]

Any air in the injector lines? Any fuel restrictions?

Both will cause your symptoms, run fine with no load (ie. revving in neutral or out of gear) but put the weight of the car on the engine and it cant rev up at all..

It might even sound like you have a bad bushing on the pumps main shaft.. it sucks in air but still allows the pump enough fuel to idle and rev freely.. but any load and it simply cannot supply enough fuel for any sort of power.

OR have you messed around with the pump at all?

[vanagonturbo]

found a nice little crack under the #2 prechamber.snipso I slapped on a headgasket and tried my luck. 

Lets start with the obvious before we go delving into diagnosing a bandaid. A crack at the prechamber (provided this is the head itself) means the head is junk. Replace the head. then we can diagnose.

For clarification, I am aware of the size of cracks between valves that is still considered serviceable. Cracks in the head at the prechambers renders the head a candidate for the recycling bin.

[lovinthedeez]

I don't think the #2 crack is the problem, although I know a new head is on the shopping list .  My question was about the hi/lo of the idle.  There are definitely no restrictions on the fuel, and I haven't messed with the pump at all.  The injectors seem to be the culprit.  Gonna get a different head and some new injectors, and see what I find.....

[rabbid79]

I agree with 8V-of-fury, this sounds like lack of fuel.  I don't see how having a crack at the prechamber could cause most of these symptoms.  Even with one cylinder completely down, you should still have 75% of the power.  Also, I don't think it would idle or start very well with one cylinder down.

Just for kicks, route the fuel lines into a container of fuel, bypassing the fuel tank completely.  Then take a careful trip down the street to see if there's any improvement.

[8v-of-fury]

Just for kicks, route the fuel lines into a container of fuel, bypassing the fuel tank completely.  Then take a careful trip down the street to see if there's any improvement.

This.

It will pretty much rule out most of the possible fueling issues.