89 350 tbi surges under 2k rpm

[Ingoldx1]

I have an 89' Suburban with a rebuilt 350 tbi. The motor is drinking anti-freeze, but that is another problem. The issue here is that the motor (especially when cold) surges and idles up and down to the point of almost stalling when being driven. It seams to run fine in park, idles short of 1k. When I drop into drive it drops to about 600. When I take off from a stand still when running like this it feels at some point like it "clears out" and runs better. I does this when ever it wants and is shortening my life one day at a time.
I have replaced:
Fuel filter
EGR
EGR control
PCV
All rubber lines
Reset timing.
I have no engine light or trouble codes popping up to help me. I am suspecting the injection controls or injectors. But as a thought could the coolant burning in the motor have anything to do with it? I have no coolant in the oil, or any spots of leaks anyware. It is being burnt in the combustion chamber.

Thanks for looking!
- Ingoldx1

[dirty dan]

Compression problems and a moist exhaust could cause problems but surging is normally caused by a vacuum leak. Check your Throttle Body to Intake Manifold and again at the Intake Manifold to Head connections . I would suspect these since it's worse when the engine is cool. Additionally, check all your vacuum hoses.
If you're loosing coolant through the cylinders, you have a much bigger problem than the surging. I would address that first.

[Ingoldx1]

I found the coolant leak, it is in the heater core. I had a big wiff of it after it got warm and then cold outside and I turned on the heater.

As far as the surging it seams that is may be flooding. I had to remove the EGR hose to get it runnig down the road (romping it or off the throttle only). It only does this now before the motor reaches normal running temps. Idles ok, but not sure what to do. I am thinking of getting it scoped to find out what is wrong.
- Ingoldx1

[dirty dan]

A scan would be a great idea. Looks like you'll need to do it on a cold engine. These old ALDL ECM's can have all kinds of problems and still not code. When you scan, I would pay special attention to the ECM's temp sensor reading.

[Ingoldx1]

I found a friend of a friend that can scan it, but he is proving to be hard to find when I need him. I found a vacuum leak at the base of the TBI today. I put a new gasket on it and it ran better, but did not fix the entire problem. I unplugged the MAP and it ran better. I replaced it an hour ago and it did not fix it, although it does have more power with the changes now. The idle is now rough and jumping after a minute or so while in park. I am thinking that the new O2 sensor may be the problem. I am going to pull it tomorrow and look at it. It idles at about 800-900rpm out gear and about 600 in gear.
TX
Ingoldx1