Hilton

Update: Solved - its a factory test-line.. see photos further down this page

Hi all,

Hopefully someone can identify this vacuum line off the bottom of the throttle body I'd love to finish putting my intake together today!

First, some basics.. my car is an '89 5-speed, so has the superior simplified vacuum system compared to the auto 'box

I've scoured the WSM and various write-ups, and have page 24-216 printed on A3 to make it easier to read.

I've accounted for the following connections and have them made off the two vac connectors on the top of the throttle body.

3x fuel pressure regulators
1x air-pump diverter valve
1x charcoal canister diverter valve

Looking at 24-216, I can't see anything else that needs vacuum other than the flappy, which takes ported vacuum from the reservoir, not manifold.

So where does this vacuum line in the picture below go to?

Thanks!

shaaark89

almost certain that one goes to the airpump diverter valve. the line coming off the top of the throttle body towards the rear should have a 4 way splitter with lines going to both dampers and the pressure regulator. the 4th line is plugged (goes to auto trans in the autos.) the forward line off the top goes to the charcoal cannister valve (fuel tank vent.)

Hilton

Possibly a RHD difference, but on my car none of the 4-ways off the splitter is plugged, and a friend with an '88 5-speed confirmed from his that the air-pump diverter is connected to the splitter as well.

The forward line off the top is the same as you say - also confirmed from the '88 5-speed.

This has me stumped.. unfortunately on his car we can't see the underside of the TB, although he's coming round here later so I might yet be able to spot it emerging from the intake somewhere. A fresh pair of eyes may spot the connection too I'm hoping.

I could just plug it, but I'd hate to discover that the car wasn't running right after putting the whole intake back together

David L. Lutz

I'm fairly confident that on my 87' this went to the air pump diverter valve. Looking on page 24-216 of the WSM it seems that the vacumm line coming from the under side goes to "I" which is called the " Secondary Air Valve" which I am assuming is the valve we are discussing?

This page in the WSM clearly show where the other 2 vacumm lines off the underside of the intake go to and its not the air pump system. I had this line pluged on mine as the air pump had been removed.

Hilton

Unfortunately the splitter isn't plugged on any sides; mine is still all connected up as the factory did it, complete with elbows on the ends of the plastic lines. I'm replacing it with all new splitter and lines and left the original plugged together for reference and measurements.

Logic therefore says that the bottom line went to something else... but I can't think of anything else that takes manifold vacuum on the car?

Anyone able to think of any other devices on a 5-speed that take manifold vacuum other than the charcoal filter, air pump, and 3 pressure regulators?

jon928se is getting here shortly and I'll be examining his '88 SE closely to check all the lines, so hopefully we'll find the answer using a mirror to peer under the TB.

jon928se

Just leaving now. I'll bring a mirror on a stick!

ROG100

That's the feed for the special valve that allows the 5 speed to simulate the power of the automatic by induced direct injection - this was omitted from the WSM to elude the not so clever owner (not you of course Hilton). If you do not connect it to the correct nipple your car will revert back to being a boreing low powered 5 speed exactly as it was delivered from the factory.
I strongly suggest you drink at least two glasses of a good Australian red before attempting this complex manouveur 8>)

Hilton

Its 11am here.. possibly abit early for a glass of red, but if we figure it out in the next few minutes I might be tempted!

UKKid35

Checkout this thread which should help

https://rennlist.com/forums/928-forum/114314-throttle-body-vacuum-lines.html

ROG100

Its 8.00pm and I am already into my second glass. Good luck!

Hilton

Mystery solved with the help of Jon's SE!

After removing his airbox and MAF and poking around with a mirror, we found it on the underside of the throttle body, and then figured out where it goes.

See the photos below - it appears to be a test port with a large rubber cap on the rear end of the RHS valve cover.

Jon's air pump valve and charcoal valve are both the same as mine (also factory - his intake hasn't been apart since manufacture).

Here are photos.. one of the line as viewed from above with MAF removed, and one of the end of it with the cap.

This probably explains the slightly high idle that I took my intake apart to fix.. mine had no cap on the line at the testing end

Oh well.. at least I know all my rubber is new and good for 20 years.

David L. Lutz

Sorry for my confusion, but I do remember now. When I deleted my air pump I also deleted that test port and pluged that line.

Thanks for this info.

By the way Roger we are about 3 BomBay's into it here on the Beach, its 10:20 and a full moon!

ColinB

Hi Hilton
Confirmation. My '89 RHD has the same line, blanked off with the same type of cap. Somebody else here (Worf?) told me it's a factory test port. BTW does your car have the 7-port vacuum tee? (Source + 6).

Colin. 89GT.

Hilton

No it has the 5 port Tee. ATs have the 7 port.

dr bob

That 'factory test port' does not attach to the vacuum system at all. It's an exhaust gas sample port from the headers upstraem of the cats, used to adjust mixture/CO. One on each side of my engine.