ByronW

I replace my heater core and evaporator core.
Now for the dumb part, there are two vacuum lines that come thru the firewall at the same location as the cores.

I can not remember where these go to, and my engine is now running and idling rough.

88 4wd 5 speed manual

Thank You,
Byron

bad_idea

One should be for the vent controls (defrost, face, floor). Do you have any vent setting other than defrost? The system is designed to fail in the defrost setting, as that is the one you need to safely operate the vehicle.

The other should be for the valve in the heater hose right at the firewall. Forget what it is called, but it is vacuum controlled and shuts off flow to the heater core when HVAC is set to cool setting. I know many people delete that valve as it is prone to failure, dumping coolant all over and stranding you.

The other end of the lines just run to the intake manifold. If the engine is idling rough, look for vacuum leaks. You can jam a small bolt/screw into the end of an unused vacuum line to stop it from leaking. I've scrapped cars with a screw still stuck in the end of an unneeded vacuum line.

ByronW

Ok thank you.
I will start looking for a leak, and in general start replacing vacuum hoses.
I guess I don't have the heater control valve, I did not see it there and I am not the one that removed it.

I thought it was strange that the engine was running really well, until I changed the cores.
Maybe coicedence.

Waynerd

If those hoses aren't connected but were before then that would be your vacuum leak.

Bugout4x4

Yep...or something under the dash got knocked loose while changing the core... Easy to do by accident.

ByronW

I changed a bad looking hose and it is running smooth again.

ByronW

I am having trouble getting the AC to blow out of the vents.
I guess a blend door is not working due to vacuum or electrical. It has 3 blend doors.

Bugout4x4

Yay! lol