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Old 03-25-2018, 10:12 PM   #1
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Idle Runs Rough. IAC IMRC?

2003 Focus 2.3L Duratec.

Engine warm or cold, the engine idle will be normal and then suddenly "chug" and drop rpm quickly and then recover back to normal RPM's. Running the AC on fan speed 4 can almost cause the engine to stall. Flipping between speed 3 and 4 can reproduce the problem. The engine normally idles around 800 rpm and drops to 500rpm and then recovers.

A few months ago I had a CEL that led me to a dried out vacuum line on the two valve bodies right on top of the intake manifold. These control the Intake Manifold Runner Control (IMRC) flats. I mention this as it could be related.

Research has pointed me to the Idle Air Controller (IAC). I have removed this part located near the throttle body and cleaned it out with throttle body cleaner. Same symptoms persist. I was not able to move the mechanism inside in or out. Not sure if it supposed to. I need to purchase a voltmeter and see if this is working as it should.

Looking for other vacuum lines that have a crack is also a possibility. There are two line that go to the IMRC valves on the top of the intake manifold route to the underside of the intake manifold and are difficult to see. I can not hear a hissing leak.


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Old 03-25-2018, 11:19 PM   #2
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You would get CEL if the IMRC was bad.
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Old 03-26-2018, 10:48 AM   #3
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The front of the intake is where the imrc/imtv gets their vac to the solenoids which are at the top of the i/m.....You'll find the vacuum actuator behind the t/b w/ the vacuum line hooked at the bottom of it. With the motor idling, Flip the t/b w/ your hand & you'll see the little imrc/actuator linkage move up/down.
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Old 03-28-2018, 09:22 PM   #4
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The vacuum actuator that is behind the throttle body works if the engine is rev'd past ~40% throttle. I can see it come up abruptly and then drop back down when at idle.

This means the solenoid and vacuum lines are working I suppose? There are two solenoids on top of the intake manifold though. Is the second one connected to another actuator?
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Old 03-28-2018, 10:07 PM   #5
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Quote:
Originally Posted by butterfingarz View Post
The vacuum actuator that is behind the throttle body works if the engine is rev'd past ~40% throttle. I can see it come up abruptly and then drop back down when at idle.
Yea that means its working......
This means the solenoid and vacuum lines are working I suppose? There are two solenoids on top of the intake manifold though. Is the second one connected to another actuator?
The imtv operates the valve for the d/r (dual runner)....The short runners are for the higher rpms & the longer runners are from idle to mid range. Works the same as the svt, but is vacuum operated vs electrical (motor hooked to a linkage) You'd have a cel on if it isn't working. btw if it wasn't working most likely the solenoid.
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Old 03-28-2018, 11:50 PM   #6
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So what do you think I should check out next?

I need to grab a voltmeter to check that the IAC is actually operating. I have read I can try unpluging it while the motor is running to see if there is a change in RPM.

I'm going to check spark plugs for the heck of it as well.
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Old 03-29-2018, 06:50 AM   #7
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Do you have a vacuum leak? It very well could be the pcv hose hidden behind the i/m. Use Denso it20's for the plugs.
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Old 03-29-2018, 06:51 AM   #8
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When cold does the motor have a high idle at first & slowly come down?
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Old 03-30-2018, 01:54 AM   #9
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Check the PCV hose buried below intake, a common duratec idle issue.

So many expect the IACs to do it but.................one needs to carefully analyze the quality of the idle. IAC generally affects SPEED ONLY, if the engine can be detected as misfiring or very erratic then may not be IAC, more the sign of an erratic air leak (vacuum leak). Most IACs are changed for nothing but then nobody pays attention to a detail of the idle quality, lottsa money wasted there.
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Old 03-30-2018, 01:00 PM   #10
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Quote:
Originally Posted by felixthecat View Post
When cold does the motor have a high idle at first & slowly come down?
Yes.
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