Let me start off by saying that any of you who have helped me to this point, thanks a million.

I won't go into many details, but some of you know that I have just gone through an engine swap and had a few "bugs" to work out. The biggest one was a slight miss at idle and a searching tach on deceleration mixed with terrible gas mileage.

I noticed today that the coolant in my reservoir was getting low. So, I started searching for a coolant leak. Found it! Heater control valve is leaking out the top. Also, I noticed that there is a "hissing" sound coming from behind my HVAC controls that won't go away (vacuum leak, right?), and air only blows from my defrost vent. I didn't figure this out until now because I haven't had air or heat on in my car since the swap.

My first question is, could a vacuum leak as small as one from the HVAC controls be causing my miss? (Please say yes ... ) I can pull the entire unit out of my parts car and replace it.

Second, could a coolant leak from the heater control valve cause a vacuum leak, too ... since vacuum runs to the valve? I plan on replacing the valve over the weekend and taking care of that.

I feel like I'm finally getting somewhere on this ... maybe.

If I can get this fixed, it's back to troubleshooting my inoperable speedo and cruise. I've ruled out the ECM so far, and a mechanic checked my VSS and said it was good. I've got another speedo sitting in the garage, but I don't think it's the speedo since the cruise doesn't work either ... thoughts? And the odometer in the spare speedo is showing 178k ... don't want that on my car if I can help it (I heard you can't roll the electronic ones back).

Thanks guys!!!

- Chris

 

The simplest solution is to plug off the vacuum hoses that go to both of them and see if the miss goes away.
In the mean time, you have to fix the HVAC problem anyway.
Everyone should have a defroster and heater unless it is a "strip-only" car.
As for the cruise/speedo problem, the cruise should work off of the VSS seperate from the speedo. If both don't work, the VSS probably isn't sending pulses out. Check that the VSS has power and ground and read continuity thru the speed sensor from the VSS plug (a schematic would be a big help).
Don't forget that a problem with the plastic gears in the trans will cause this problem too...

 

Thanks.

I am looking forward to testing the vacuum to see if it remedies my problem. What's the best way to plug off the lines? Stick a golf tee in them or something? Do I need to plug off each individual line on the HVAC controls?

Again though ... could the HVAC vacuum leak be enough to make the car miss at idle?

My mechanic said the speedo gears looked fine when he took the VSS off. Is there any possible way that the speedo gears couldn't "connect" with the VSS in place. The gears are brand new and were installed when I did my tranny rebuild and rear end swap (along with the motor swap) just a couple of weeks ago.

Won't get to do anything this evening ... dropping off our baby girl with my parents and taking my wife out. Sometimes the car has to come second.

 

Just plug off the one vacuum line that goes thru the firewall (golf tee will do). This will stop the vacuum to the heater control valve since it is fed vacuum from the HVAC control.
The VSS (vehicle speed sensor buffer) I was refering to, is a box inside the car (if the '92 is the same as an '88). Not to be confused with the transmission speed sensor which has the plastic gear on. Need a schematic to be sure.

 

I thought only the TBI cars had wires running from the VSS to a buffer box.