Is a vacuum hose supposed to go here? What would it attach to? (Page 1/3)
stapler8 OCT 16, 06:51 PM
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I'm about 99% sure that I'm missing a hose there, but I haven't a clue where the other end should go.

Where would I get the hose too? Would NAPA have that sort of thing?

'84 SE/4-spd.
Blacktree OCT 16, 07:15 PM
There should be a vacuum line running from there to the air filter canister. There should be a temperature sensor attached to the side of the canister. Also, there should be a second vacuum line running from the temperature sensor to a vacuum port on the throttle body.

Just FYI, that hockey puck looking thing is the Thermac valve. It helps the engine warm up when it's cold outside (by pulling heat from the exhaust pipe). It's not a critical system, but will make your life easier when it gets cold outside.

I don't remember what the hose size is. But it should be a common size. (I'm thinking 3/16"?)
AsaBergman OCT 16, 07:18 PM

quote
Originally posted by stapler8:

This images is larger than 153600 bytes. Click to view.

I'm about 99% sure that I'm missing a hose there, but I haven't a clue where the other end should go.

Where would I get the hose too? Would NAPA have that sort of thing?

'84 SE/4-spd.



That is for the Thermac air cleaner valve. It's purpose is to pull in hot air from above the exhaust when the engine is cold and then switch to the normal intake duct when warm. If you take the lid off the air cleaner you'll see a little non-electric device connected to the bottom, this is a temp switch. On the bottom of it are two vacuum connectors. One of these vacuum lines connects to that valve you pictured, the other goes to the throttle body.

Issue is by now most of those thermac valves are faulty and/or the temperature switch is faulty. I noticed mine was bad and was keeping the thermac valve shut at all times constantly pulling in hot air from above the exhaust rather than the intake ducting through the side of the car so I disabled it. My engine warms up just fine without it. I'd say just leave it disconnected. Ensure the unused port on the throttle body is properly capped off though.

[This message has been edited by AsaBergman (edited 10-16-2019).]

stapler8 OCT 16, 07:32 PM
Could this be the reason why my car idles perfectly (1100 RPM) while warming up, but once warm idles at about 2K RPM? What can I do about this?
Patrick OCT 16, 08:06 PM

quote
Originally posted by stapler8:

...once warm idles at about 2K RPM?



That's usually an indication of a vacuum leak.
stapler8 OCT 16, 08:08 PM
Is there a list somewhere of all the vacuum hoses that I can check? Could this one (which I know for sure is missing) be the cause of it?
AsaBergman OCT 16, 08:10 PM

quote
Originally posted by stapler8:

Could this be the reason why my car idles perfectly (1100 RPM) while warming up, but once warm idles at about 2K RPM? What can I do about this?



Here's an odd bit of info from personal experience, are you positive you have the correct ECM in your car? When I got my 84 4 speed I had weird idle issues and the shift light would come on at odd times. It drove perfect but when I'd come to a stop sign it would idle at 2k for no reason, the check engine light would come on but then after 30 seconds or so the idle would drop. I discovered the previous owner put in an 85 AUTO ecm. Switched to a proper 84 manual ecm and it works perfect now.

Assuming you have the correct ecm I'd suspect either a vacuum leak or bad temp sensor. You should ensure there isn't a vacuum line still attached to that thermac temperature sensor and if so disconnect the line from the throttle body and cap it as without the valve attached it would be a vacuum leak. If that's not the cause it may be the temp sensor in the thermostat neck if you've never replaced it.
stapler8 OCT 16, 08:14 PM
Asa:

My only engine code is for the TPS, which showed up after I replaced it. Neither me or my mechanic can figure out why it's still throwing the code, but the idle seems to be fine.

The engine naturally revs at about 2K, which also means my upshifts are very jerky. Thermostat replaced a month ago.

Is the thermac temp sensor you're talking about the thing in my picture, or somewhere else entirely? I'm not very experienced with Fieros yet admittedly.
AsaBergman OCT 16, 08:44 PM

quote
Originally posted by stapler8:

Asa:

My only engine code is for the TPS, which showed up after I replaced it. Neither me or my mechanic can figure out why it's still throwing the code, but the idle seems to be fine.

The engine naturally revs at about 2K, which also means my upshifts are very jerky. Thermostat replaced a month ago.

Is the thermac temp sensor you're talking about the thing in my picture, or somewhere else entirely? I'm not very experienced with Fieros yet admittedly.



First rule, a new part doesn't mean it's a good part.
When I had the wrong ECM it was giving me an error code for the VSS.
My 84 idles at 1k after it warms up, idles at 2400-2600 when warming up.

Here are two pictures, one of the sensor(pointing a screwdriver at it) other picture is of the bottom of that sensor with the two vacuum lines:
AsaBergman OCT 16, 08:46 PM

quote
Originally posted by stapler8:

Is there a list somewhere of all the vacuum hoses that I can check? Could this one (which I know for sure is missing) be the cause of it?



If that line is missing but the sensor is still hooked up to vacuum then yes, it could be the cause.

Every vacuum line on an 84:

MAP sensor, short hard line. Leftmost vacuum port on throttle body.
EGR valve, short hard line. Port to the left of the large PCV line.
Both of these hard lines can have difficult to see cracks.

Charcoal canister has two, vent and purge. One goes to throttle body, other goes to intake tee. Charcoal can has two metal lines bolted to trunk with rubber lines on each end.

Cruise control, one line from that intake tee. A second line connecting the vacuum can to the cruise servo, I believe a third connecting to the purge switch. You should disconnect the vacuum line leading to the cruise and cap it first as that is expendable if leaking.

Brake booster, thick rubber line attached to the intake tee.

PCV valve has one thick rubber line, due to old grommets on the valve cover the PCV system can be a vacuum leak.

Thermac air cleaner, one line going from throttle body(port to the right of PCV line) to the sensor on the air cleaner, second line going from that sensor to valve.