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ok showing my cards here as a novice....what and where is the butterfly valve.? Is it valve that shuts the flow off to the heater core when the temp selector is set to hot and vice versa when it is set to cold?.

 

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Actually what this does is when you switch to AC it closes off the coolant flow to the heater core. The temp control cable just switches open and close the blend door.

The valve is on the front coolant line (close to the front clip not the rear one close to the fire wall)

In more R&D to the no or limited heat issue (heater cools at idle but good to HOT at higher RPMs) this is what I have found:

It is more so due to a cheap and malfunctioning T-Stat, it is staying open and not closing and allowing the coolant to cool down faster (most reported this after trouble shooting the water pump / heater core / Heater lines / HAVC controller / vacuum lines)

This along with the known problems with the aftermarket water pumps (cheap remans) are the two main causes of low to no heat at idle.

In our wonderful Sub 0 Temps here in MN, I am going to attack my T-Stat as I have already exhausted all other options. Kind of wished that I had taken this route first before going after the other options. It was my bad for figuring that it was as it was, opening like it should once warm, that it was functioning as it should in all ranges. But while watching the coolant flow (with radiator cap off) when it was warm, I noticed that no matter how long I ran the engine, the flow never stopped (it just kept moving for like 10 min non stop). Hence the T-stat is not closing when it cools down below 195 or so allowing heat to rebuild in the cooling system to provide ample heat.

 

Hawkstr.

I already changed the t-stat only to discover the one I replaced was working just fine. I replaced the water pump a few years ago....BUT I was having this issue before I replace said water pump. I am convinced that the water pump is too weak to handle pumping the coolant and idle speed.

Are there any water pumps that I can get which will increase the coolant flow at idle?

 

Sounds to me like you are not having a water pump problem but there is still enough blockage inside your heater core (even after the back wash) preventing proper coolant flow. You may want to try a chemical flush of the entire system or replacement of the heater core.

If you are convinced it is the pump then the best NEW replacement water pump I have found is the Duralast from Auto Zone model CWP-9126 priced at only $60. This P/N was for my '97 3.9L V6 so you should double-check for your '98 application (but I think it should be the same).

 

After the sub 0 effect wore off, I came to find what was suppose to be a 195 T-stat was really a 160. No wonder it was freeking cold air. The package said 195, but the bottom stamp on the T-stat says 160.

So don't take the package to heart that it's what you have in there. Check the bottom of the T-stat to make sure before all the headache of putting it all together and finding not enough heat.

If you back flushed and had any gunk come out but still find some gunk lined in the hose, then do a full system flush as Rusty93RamVan says or just cut to the chase and replace the heater core with a new one (rockauto has a new one at a really good price).

I have by-passed the main valve (that shuts off flow to the heater core when AC is turned on), also did the same for the rear heater one just cause its winter here and I can put them all back in spring. Going to replace the rear heater lines in spring any way (cause one suppose to be 1/2 other suppose to be 5/8, but both are 5/8 so someone goofed up before I got it also they are rough shape sure they will last the winter at least)