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Discussion Starter · #1 · (Edited)
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Hello! My 2002 Mercury Cougar V6 Automatic idles lean when in drive and reverse at a stop. In neutral it idles perfect.

More Context: When the engine is warmed up the lean idle stops but the rough idle occurs a few minutes after starting up. The rpm sounds like it's going to stall but it doesn't. It does not trip any codes. It idles normal around 800 rpm and then it dips to 650 sporadically at a stop. I recently replaced the fuel injectors, sparks plugs, intake gasket, fuel filter, EGR valve, and even the IACV, but it still has this issue. The fuel pump was replaced from that 2004 recall, and I swapped the air intake & MAF Sensor from another Cougar and no fix.

I would appreciate any advice. :) Long live the Cougs!

Update: [F68E-6758-AE / M536K is a part that I may or may not need to replace to fix the vacuum leak. I wrapped tape over it & the idle is still rough]
 

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1999 3.0 SilFro
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You can use any old piece of rubber hose in the right size. Just route it so it doesn’t make contact with the water pump pulley. If that solves your problem THEN you can try to find a factory part later.
 
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Discussion Starter · #3 · (Edited)
Thank you for the suggestion! I will look for a universal rubber tube and measure the hole diameter.
Also I learned that part is called a positive crankcase ventilation hose; however, on the Ford parts website, all the hosing parts are discontinued for the Cougar, but I will keep searching in due time.
For now I bought self healing tape from AutoZone. I will share the results and see if the tape calms the lean idle in gear. 👍
 

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1998 V6 MTX Ebony Black Wild at Heart Trim
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I used a piece of replacement PCV hose (something fuel/oil vapor proof) from the roll my father had left in the garage.
It doesn't have the bends for the IMRC but you only notice it if you look really close.

The only BMW part I would ever put on the car haha
 

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Discussion Starter · #5 · (Edited)
Thank you MarcusV6, I am starting to find rolls of that PCV hose online. The Motorcraft rolls for the 3.8-4.8mm or the 5.1-6.1mm are $100+ on Rockauto or Ebay, but cuts of it are $10-$30 from generic brands. I haven't measured the diameter yet, after realizing I need to test the other hoses.

But yeah I did tape that visible PCV hose and the lean idle still occurs.

Also I learned that the EGR system is activated when the engine is warm which explains why my Cougar's idle becomes stable when warmed up, so likely it is a vacuum leak somewhere. I'm thinking I will take off the front plastic cover on top of the engine & try the Water Soak/Mist test or get it smoked tested to find the leak on the vacuum hoses.

These are pictures of the top view:

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Motor vehicle Hood Automotive design Automotive fuel system Automotive exterior


Also do any of you recommend me buying the "Powertrain Control/Emissions Diagnosis 2002 Service Manual" that's referenced by the hood sticker?
Font Rectangle Material property Parallel Pattern
 

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Most of us believe that plug wires should be replaced with the plugs on these cars, and I also believe the ignition coil on the 01/02 cars needs to be replaced every 75k miles or so.

This does sound more like an air leak though.
 
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Discussion Starter · #9 ·
Wow thank you so much for that link mmc757, and wadespencer99 for your suggestion! I just ordered the 02 book. After looking through that 1998 pdf it's teaching me more about this engine, it will be worth it when it comes in, especially since the C2 Cougar may have a different pcv set up.

This Cougar is actually my Dad's car and it just hit 105,000 miles. I will look into the ignition coil and wires, good idea for maintenance.

I have finals this week so I will try to get it diagnosed soon, indeed I will not give up. I love these cars. Thank you everyone for providing me knowledge!
 

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Discussion Starter · #10 ·
Also I'm sorry it's been a while. Life got busy and I haven't been able to drive the Cougar for a while. The smoke machine did come in and I hope to test it soon to find the vacuum leak and use automotive tape for a temporary fix. I promise one day I will share the results.
 
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