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Discussion Starter · #1 ·
I am back after a very long time. I no longer have the 1995 or 1996 Thunderbirds. Me and my wife were missing them so we decided to look around for another MN12. My wife saw this green 1994 T-Bird and had to have it. It has 57,000 miles and the previous owner did "the PI Swap" to it.

Now I am doing a lot of research to make sure it involved with this swap. It runs fine except when it is cold the idle drops so low it stalls. This symptom only lasts for about 30 seconds.
I did find unused ports on two vacuum trees. I connected the climate control line and plugged the rest. I a 1994 Ford Electrical and Vacuum Troubleshooting Manual in the trunk, that is nice but photos of how vacuum lines run along the firewall would help too.

Good to be back.
Rich
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SuperNewbie
1995 Thunderbird LX 4.6 red
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Very nice! This car agrees with me. My first MN12 was a green 1994. If you still have idle issues, start looking for vacuum leaks. Do you know if the car was tuned after the PI swap?
 

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Discussion Starter · #3 ·
Thanks!
Yes it was tuned. The SCT X4 tuner came with the car. I know there must be a vacuum leak somewhere in the climate control system. Could be at the inner fender reservoir. Air blows only out of the defrost vents.
 
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1994 Cougar XR7 DOHC/5-Speed
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Check if there’s a loose vacuum line under the passenger side dash, it’s very common for that one to get knocked off the servo by a passenger playing footsie with the car, and with it unplugged all air will direct through the defrost vents by default in all settings

The firewall vacuum lines shouldn’t be altered whatsoever with the 96-97 conversion besides the main vacuum line off the plenum to feed the tree, which goes to the brake booster, HVAC and cruise control servo, which appears to be deleted in the picture of your engine bay. The vacuum reservoir line comes off the check valve near the AC evaporator connections
 

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Discussion Starter · #5 ·
The white line under the dash is fine. Under the hood it is connected to the check valve.
Not concerned with the cruise control, I never use it anyway.
I will draw a diagram off the current vacuum line configuration. Sneaky feeling that it is not quite right.

Here is a list of what the PO did to it:
Below parts are installed on or after September 2020:

Pi Heads/Cams swap off a 2004 Mustang GT (66k miles on them). Pi Intake swap.
SVE 75mm Throttle Body and Plenum.
New 14 piece steering/Suspension kit, bushes, sway bars etc. (installed)
New 2.5" duel exhaust with X pipe (tru bendz).
New Vogtland 1.6” lowering springs installed.
New Front struts and rear shocks. installed
New Custom Paint job: (Metallic Dark Green).
SCT X4 $155+$150 unlock fee + $200 email tune from Lasota Racing.
New coil packs and spark plug wires and new Motorcraft copper spark plugs. (Feb 2021)

New Battery and New 130Amp Alternator. (Feb 2021)
New Tires & Wheel alignment. (Sept 2020)
Tail light LED lights replaced with stock HP LED strip Replacements x2.
New headlights and upgraded to LED bulbs.
New Fuel Filter.
Taillights/Headlights Tinting All Windows tinted in December 2020.
New K&N Air Filter replaced. (Sept 2020) New PCV Valve replaced.
 
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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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I'm not a huge fan of tinted windows/headlights/taillights but in this case it was done tastefully and the overall impression pops. It's a sharp car. :)

Why'd the PO sell? Based on the list of things done, it sounds like they intended to keep it for quite a while.
 

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Nice car! Welcome back! This has been the year for quite a few old members to return.
 

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Discussion Starter · #10 ·
I'm not a huge fan of tinted windows/headlights/taillights but in this case it was done tastefully and the overall impression pops. It's a sharp car. :)

Why'd the PO sell? Based on the list of things done, it sounds like they intended to keep it for quite a while.
Yeah. I don't care much for the tinted windows and headlights either. I will probably remove the film on the headlights and definitely go with a lighter and legal tint on the windows. And thanks!
the seller had to back home to Australia. his visa ran out plus had to get back to work on a TV show there.
 

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1994 Cougar XR7 DOHC/5-Speed
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“New 14 piece steering/Suspension kit, bushes, sway bars etc.”

These kinds of kits tend to use very low quality parts. Some of the lower priced suspension components work fine and aren’t critical enough to stress about but UCAs and LCAs in particular you really should stick with professional grade stuff, not sold in kits.
 

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Discussion Starter · #12 ·
I see why it is not getting vacuum to the climate control. The brake booster is hogging all the vacuum.
I drew a quick diagram of how it is now.
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1994 Cougar XR7 DOHC/5-Speed
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That’ll do it, factory 96-97 plenums have a dedicated port for the brake booster where Mustang plenums (and all aftermarket ones) lack it since they’re hydroboost. Just add another T in the booster line to the plugged hose send you’ll have HVAC and as it turns out cruise - Vac tree 1 going into the inner fender goes the cruise servo, I stand corrected, I couldn’t see the lines for it in the picture.

I see another problem, your diagram is missing the PCV valve, it should have another port at the front of the plenum. If PCV were fully deleted (which I don’t recommend) both the PCV valve and the breather hose would be replaced with breather filters, but the line is clearly hooked up. Without the valve, or whatever’s in its place you’re drawing unmetered air through the passenger side valve cover through the crankcase and into the driver side breather tube through the intake system.
 

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Discussion Starter · #14 ·
That’ll do it, factory 96-97 plenums have a dedicated port for the brake booster where Mustang plenums (and all aftermarket ones) lack it since they’re hydroboost. Just add another T in the booster line to the plugged hose send you’ll have HVAC and as it turns out cruise - Vac tree 1 going into the inner fender goes the cruise servo, I stand corrected, I couldn’t see the lines for it in the picture.

I see another problem, your diagram is missing the PCV valve, it should have another port at the front of the plenum. If PCV were fully deleted (which I don’t recommend) both the PCV valve and the breather hose would be replaced with breather filters, but the line is clearly hooked up. Without the valve, or whatever’s in its place you’re drawing unmetered air through the passenger side valve cover through the crankcase and into the driver side breather tube through the intake system.
Thanks Matt. Here is a photo of the the PCV valve setup.
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Discussion Starter · #15 ·
I still need to track down the vacuum leak causing the cold idle issue. it starts and holds an idle just fine. If I give it a little throttle it responds without hesitation but then the RPM drops so low it stalls out. Here are some pics of cold idle in Park and in Drive. The RPM looks ok, maybe a little low?
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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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Factory idle speed is 600 RPM in park/neutral and 550 RPM in drive, with a few adders based on ECT when startup occurred.

Definitely running lean though, it's at the limit of adding 25% fuel to compensate.

The photo you posted is of the vent - the PCV valve is on the passenger side. The driver's side is just a vent to allow filtered, metered air back into the sump as vapors are pulled into the plenum for combustion.

On the 96+ factory setups the lower front vacuum port is for the PCV valve. The other port on the front (near the throttle body) is for the EVR/EGR solenoid. There is a second upper front port above the EGR inlet for the brake booster/HVAC tee; a port on the rear is for the EVAP system.
 

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Discussion Starter · #17 · (Edited)
Thanks Brandon.
I went out to look at the right side valve cover and did see the PCV valve with two lines coming from it. It is too dark out to see where they go. I also noticed a plugged port on the throttle body just after the TPS.
I will get a better look in the daylight.
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Looking through your list again, It's funny that you've listed a New K&N filter as they're lifetime filters. Just clean and re-oil the thing. No need to replace.

I'm also not a fan of the tinted head and tail lights. Glad to read that you plan on removing the tint.
 
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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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Yeah, it's hard to see what's going on. Yank the air intake tube and poke around a little, it's much easier to see the routing with that out of the way. The EVAP is a plastic hard line that runs along the top of the passenger side valve cover from the back of the plenum, then jogs across to the passenger shock tower and goes into the inner fender along the frame rail.

Here's a pair of images - one that I annotated to help show what and where, then another without the annotations so it's easier to see everything.

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