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OP has the symptoms of a vacuum leak. Don't be surprised if IAC doesn't fix it. So many of you swap the IACs to get multiple problems when commonly they are not the problem. Vacuum leak is why no code shows until WAAAAY later, I've personally seen years to get one.

The rising and falling of rpm tells you the IAC is ranging properly, trying to fix the issue but the issue being not fixed will vary as most vacuum leaks do. The IAC goes low and so does the vacuum leak as engine rpm has decreased, and the same the other way too when the IAC then overcompensates too high for the engine speed slowing down the leak amount. What results in the infinitely variable 'rrr RRR rrr RRR' high/low rpm thing. Dunno why so many of you can't get that part.

So many change the IACs for no reason, the rpm suddenly going all over the place is enough for them but commonly it's NOT the IAC doing it.

To other, the IAC setting screw is to center the range of the pintle, that center will also vary the optimum amount of air perceived by the PCM. The center point is as important as the overall air amount setting, they both have to happen at the same time. Or as close as possible, it prevents unnecessary IAC ranging that wears the part out faster. And if too far off it will result in a IAC range limit code and pretty fast if it is a solid problem. The code will say something like IAC cannot control the rpm or similar.

OP's Dad should have known there is a quick setting to set the carb choke 'break or qualifying' setting on a Q-Jet. It can be adjusted correct for the weather conditions in seconds. And, if the linkage was correct and adjusted right to begin with simply pushing down gas pedal further opens that plate up more too. It is anti-flood prevention built right in.
 

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Discussion Starter · #23 ·
OP has the symptoms of a vacuum leak. Don't be surprised if IAC doesn't fix it. So many of you swap the IACs to get multiple problems when commonly they are not the problem. Vacuum leak is why no code shows until WAAAAY later, I've personally seen years to get one.

The rising and falling of rpm tells you the IAC is ranging properly, trying to fix the issue but the issue being not fixed will vary as most vacuum leaks do. The IAC goes low and so does the vacuum leak as engine rpm has decreased, and the same the other way too when the IAC then overcompensates too high for the engine speed slowing down the leak amount. What results in the infinitely variable 'rrr RRR rrr RRR' high/low rpm thing. Dunno why so many of you can't get that part.

So many change the IACs for no reason, the rpm suddenly going all over the place is enough for them but commonly it's NOT the IAC doing it.

To other, the IAC setting screw is to center the range of the pintle, that center will also vary the optimum amount of air perceived by the PCM. The center point is as important as the overall air amount setting, they both have to happen at the same time. Or as close as possible, it prevents unnecessary IAC ranging that wears the part out faster. And if too far off it will result in a IAC range limit code and pretty fast if it is a solid problem. The code will say something like IAC cannot control the rpm or similar.

OP's Dad should have known there is a quick setting to set the carb choke 'break or qualifying' setting on a Q-Jet. It can be adjusted correct for the weather conditions in seconds. And, if the linkage was correct and adjusted right to begin with simply pushing down gas pedal further opens that plate up more too. It is anti-flood prevention built right in.
He knew that it didn't help that's why I used a clothes pin He knew that it didn't help that's why I used a clothes pin.
 

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I chased a vacuum leak for over a year once trying to catch it messing up until I learned what to look for that pretty much tells you instantly it is a leak. The leak reseals up and then you can scan until the end of earth and get nothing. Keep trying though.

Ford damps code response in order to confuse more people into going to the dealers, like the temperature gauge thing that does the same thing.

'He knew that it didn't help' is absolutely incorrect, the choke can be held 100% wide open if you want to and no clothespin needed to do it. I used to rebuilt scads of those carbs. If Dad knew what to look for he likely would have cured the issue and commonly not the choke at all, it's just that the choke can affect it to work. The problem was leaking main wells in the carb castings and Q-Jets well known for it for many years.
 

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Discussion Starter · #26 ·
Many parts can impair AFR and driveability without setting codes. EVAP purge valve, PCV valve, EGR, etc. Without codes, make your best guess and see what happens.
I think it's APC V it's never been replaced all I replaced was at long back hose when it didn't pass smog the hose had collapsed but I never put APC V in it yet
 

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The PCV valve cannot leak, only clogs up and that lowers idle not raises it. The long back hose may be leaking again, if like a Dorman part, their rubber lasts maybe ten minutes. The worst rubber on earth for long life.

Bear in mind the TB base gasket has a thin seal at the IAC bypass that can blow out to leak and it shows at cold start to get much better when engine goes to closed loop and warm. When leaking the IAC settings go to h-ll. The seal can also seal back up again to quit leaking until it decides to do it again.
 

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Discussion Starter · #28 ·
The PCV valve cannot leak, only clogs up and that lowers idle not raises it. The long back hose may be leaking again, if like a Dorman part, their rubber lasts maybe ten minutes. The worst rubber on earth for long life.

Bear in mind the TB base gasket has a thin seal at the IAC bypass that can blow out to leak and it shows at cold start to get much better when engine goes to closed loop and warm. When leaking the IAC settings go to h-ll. The seal can also seal back up again to quit leaking until it decides to do it again.
Yeah it's set for 2 days and when I started up it started up like AV8 with like a really lumpy idol where I put a scanner on it and it was going between like 750 and 400 RPMs seconds later went up to the 1200 like I'm supposed to smooth down never did it again
 

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You can also check fuel pressure and should be around 40 psi at idle then shut engine off and watch for how fast the pressure bleeds back down. It should stay close to the same for at least an hour to me. Going down quick is a leaking injector that will start up just like you describe. The fuel line leaks down that cylinder to be loaded with fuel at a start and why it sounds lumpy like that.
 

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Discussion Starter · #30 · (Edited)
That's exactly what my mechanic friend said last year , I guess I'm just in denial. It's not hard to replace those myself is it ? The price would have been lower last year. : ( what about that weird high idle the one time that took like 10 minutes to come down ? To me it acted like the IAC was stuck at 1200 rpm high idle for awhile. My pressure is right there (40) per scanner. Can I rent a gauge and put on Schrader port to test it. ?
Or just bite the bullet and buy 4 new ones. 😂
Also could the TB base gasket you described be the problem ? Lumpy idle ? Or just the stuck high idle for awhile.
 

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To me it acted like the IAC was stuck at 1200 rpm high idle for awhile
That tells me to replace the IAC. It's old and due for PM anyway. What more do you need to know.

My pressure is right there (40) per scanner. Can I rent a gauge and put on Schrader port to test it.
You can but why. I trust what Forscan tells me.

Or just bite the bullet and buy 4 new ones
That's a big bullet to bite. I would do easy jobs first.
 

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Discussion Starter · #32 ·
I have a mechanic friend with professional scanners and all he was a mechanic for many years at different dealers would he be able to do a pressure drop test using a scanner or do you have a gauge on the fuel rail ?
 

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Wow!

The IAC is just a simple solenoid actuated air pathway. When the throttle body butterfly is fully closed, the IAC allows air to be channeled into the intake manifold plenums. The computer will put voltage down on the IAC to open and close the valve, but just assumes it works, and cannot trigger a fault code.

Troubleshooting is difficult, but simple, since your probably looking for a leak of unrealized air. Additional air that is either metered by the Mass Air Flow sensor, or un-metered such as a leak that wasn't measured by the Mass Air Flow meter.

I would take the throttle body off, stuff a rag in the intake manifold to block anything from dropping in it and clean the edge of the throttle body butterfly, and scrub the intake manifold plenum. You want to make sure you have a tight seal when the butterfly closes, so air actually passes through the IAC valve channel. If you have carbon build up on the edge of the butterfly, air will leak and the IAC channel and valve will make things worst by adding even more air.

Best fix is to just buy a new throttle body gasket, new IAC valve gasket, and clean the IAC, or replace it with a decent one like the Hitachi, and clean the throttle body system. If you still have an issue, then your consuming un-metered air. This could be a hose, or intake manifold gasket.
 

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I have a mechanic friend ... would he be able to do a pressure drop test using a scanner
IDK, but I can with Forscan.

I pull the fuel pump fuse so it can't run. That prevents re-priming the pressure. Then I go KOEO (key on engine off) and connect with Forscan to read the number. It's that simple.

With engine off, my fuel pressure holds at 40 psi for an hour or more. That rules out injector leakage. It bleeds off overnight, but that's normal.

More info: www.agcoauto.com/content/news/p2_articleid/323

o_O
 

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UH, the butterfly does NOT fully close and never should. The IAC range is set up for a certain amount of air to go through the butterfly aircrack that is at idle. Why the setscrew to set that 'leak'.

I clean pretty much most of my butterfly without ever removing the TB, simply open the throttle and clean the edges of it. I have never cleaned the inside of an intake and no need.

Lumpy idle and high idle rpm are two sides of the same coin. Likely vacuum leak. You can have that leak and fuel pressure one from injector too, no law says otherwise. If you hold pedal down to stop flooding the other three injectors will be off too and engine may well not start at all.

And yes, I likely have the only two Focus cars in the US with schrader valves on the intakes.
 
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