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Discussion Starter · #1 ·
Hey there, I'm having some issues with my 2002 Focus SE. I got a new serpentine belt and IAC valve installed yesterday, however it made my problem significantly worse. Now when I start the car it
-Revs very high immediately before settling down, my car tries to get me to 50mph on a flat road if I don't use my brakes
-When I come to a complete stop occasionally it feels like my engine is tugging me, or alternatively this is when the revs drop down and it will occasionally stall, triggering the battery oil and check engine lights.

The reason I installed a new IAC is because my car would occasionally stall with the AC on when coming to a stop, now my issue happens regardless of AC being on. I replaced the battery yesterday as well and reset my ECU, however the problem still persists. Could it be a faulty IAC or something else entirely?
 

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2004 ZX3 SVT EE 160k miles. 2004 ZX3 SVT 189k miles
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Check for a collapsed pcv hose coming out of the back of the intake. Dont just look at it. Remove it completely and examine it thoroughly.
 

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It runs around the driver's side, to the rear corner of the engine. It is obscured by stuff on top, but look carefully between the firewall and intake.

What typically happens is it gets soft over time, to the point that engine heat and suction will collapse it, restricting air flow.

If you are going to remove it for examination, I would recommend you just replace it, since it's a bit of a pain to get to.

Try this crummy video:

 

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As if on cue...haven't watched this one, but this guy's videos are all really good:

 

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Discussion Starter · #6 ·
Awesome you guys helped a bunch, I knew this could be an issue from hearing about it before on this forum, I just never had actually been able to find it or have symptoms directly related to it. Upon inspection I discovered my tube was collapsed at the bend, even prior to starting the car, and squishae between my fingers. Because there's not a particularly good video to do it and it's pretty cramped in there I took it to the mechanic yesterday and it's getting a new PVC valve and hose today.
 

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Discussion Starter · #7 ·
Upon receiving my focus back from the shop I noticed it still has some issues. When starting it still revs up pretty high, but that could be because of the cold. However my car still seems like it just wants to move. It either tries to idle and bring it up to 50mph, or occasionally, probably half the time or a quarter, when I come to a stop it either feels like the engine is fighting me braking, or it will essentially stop vibrating and noises entirely and then stalls.
So far since I got the car I've replaced the:
  • Radiator
  • Spark Plugs
  • Timing belt
  • Valve gasket cover
  • Serpentine belt
  • IAC
  • PVC valve & hose
  • Coolant Flush with rad & Oil changes every 7.5k
At this point I'm having a hard time thinking about what could be causing this, having replaced what I would've thought were the big things. Do first gen foci get throttle body / sensor problems? Should i just take it in to be diagnosed?
 

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2004 ZX3 SVT EE 160k miles. 2004 ZX3 SVT 189k miles
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Upon receiving my focus back from the shop I noticed it still has some issues. When starting it still revs up pretty high, but that could be because of the cold. However my car still seems like it just wants to move. It either tries to idle and bring it up to 50mph, or occasionally, probably half the time or a quarter, when I come to a stop it either feels like the engine is fighting me braking, or it will essentially stop vibrating and noises entirely and then stalls.
So far since I got the car I've replaced the:
  • Radiator
  • Spark Plugs
  • Timing belt
  • Valve gasket cover
  • Serpentine belt
  • IAC
  • PVC valve & hose
  • Coolant Flush with rad & Oil changes every 7.5k
At this point I'm having a hard time thinking about what could be causing this, having replaced what I would've thought were the big things. Do first gen foci get throttle body / sensor problems? Should i just take it in to be diagnosed?
This car has a plastic throttle body that will stick when dirty. Clean it.
 

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2004 ZX3 SVT EE 160k miles. 2004 ZX3 SVT 189k miles
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Get some mass airflow specific cleaner from the auto parts store. You can spray the mass air flow sensor and clean it. Use the same spray to clean the throttle body.
 

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2004 ZX3 SVT EE 160k miles. 2004 ZX3 SVT 189k miles
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I believe the intake tube has a permanent clamp type from the factory. Replace with a regular hose clamp.
 

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I believe the intake tube has a permanent clamp type from the factory. Replace with a regular hose clamp.
And also be sure not to crank it down too tight. The plastic throttle body bore can deform and that'll also cause the throttle to stick.
 

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Discussion Starter · #12 ·
Is the throttle body the most likely source? It's kinda like I have my foot pressed a little on the gas when I'm in first gear, and then it will lose significant rpms and stall. It only has issues when I'm idling or coming to a stop, and it's not everytime, but I can almost feel it coming because the engine is making significantly more noise, regardless of not having a tach. Also it used to idle like a normal car and creep along at a couple miles per hour before I got my IAC and serpentine belt done, whereas now it usually wants to climb up to at least 30, and sometimes 50.
 

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Discussion Starter · #13 ·
Well I cleaned the throttle body, and it hasn't stalled again but it still fights me when I'm braking, almost like I'm engaging the gas when I'm not, and it won't die down until I put it in nuetral or park, where it drops to normal rpms.
 

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Well I cleaned the throttle body, and it hasn't stalled again but it still fights me when I'm braking, almost like I'm engaging the gas when I'm not, and it won't die down until I put it in nuetral or park, where it drops to normal rpms.
Almost sounds like a vacuum leak in the brake booster. I would check the hose for damage and pull a vacuum on the booster to test for leakage.
 

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2004 ZX3 SVT EE 160k miles. 2004 ZX3 SVT 189k miles
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Other possibility is a bad throttle position sensor. You need a scan tool to see what is going on instead of throwing parts at it.
 
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