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Discussion Starter #1
I have a 2002 Focus SPI. When I first got it I was unable to keep it running so I messed with the idle screw to keep it from stalling out. I have since fixed all of the problems keeping it from running and tried to put the idle screw back to its correct position but some of the mark I put on the screw came off so I'm not sure if I have it correct. It idles ok but it seems to lunge forward a bit when put into gear and seems to coast a little too quickly .

I have FORScan set up. Is there a way to get it exact?
 

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Too low, the IAC will be toward one end of its' range and then takes too long to respond leading to problems. Also, being at the end means you run out of bumpup adjustment say with a/c switched on. It'll work but not optimum.

Don't even need software. Warm engine up and disconnect the IAC harness and then adjust the idle speed to say 650-700 rpm then plug the IAC back in. That will have the TB butterfly set a bit low, the IAC then comes on to adjust slightly upwards (750ish) and still plenty of bump room for it at say a/c coming on. Older higher mileage engines will love it too.

You want the IAC not working speed slightly lower than with it on to have full IAC control but still be close to the proper centered-in-range position.
 

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AMC, you underestimate the range that the IAC has. If you set the idle to 700 with it unplugged you will likely get an error code. The TPS voltage will also be too high. The PCM often desires / commands an idle speed below 700. He is looking to set the absolute minimum base idle. The IAC is always working, and it should be working at 35-45% duty cylce on a warm idle without much electrical draw. If he sets the base idle to 475-500, that's about where it will sit.
 

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Discussion Starter #5
I turned the screw past where I knew it was before and the idle is still high. TPS voltage was about 0.97 before adjusting and 0.94v after. I was able to get it down to about 980rpm but I didn't want to go down further without checking in here first. I have attached a screenshot after plugging the IACV back in. What else could be causing the high idle?
 

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Vacuum leak.

To other...........

'The PCM often desires / commands an idle speed below 700.'

I disagree with that. The absolute hot idle speed is set in software whatever it is (MTX may be slightly lower) and the PCM seeks to hit that number except at cold start which bumps up in a ramp based on it as well. There is NO reason to go lower, and it increases emissions to do so. Several other bad things happen at lower rpm as well.

'AMC, you underestimate the range that the IAC has.'

Uh, no. I am fully aware of the wide range it has, in this case you misunderstand the importance of the IAC ranging being kept closely to the software idle speed. It's not nearly so important on newer vehicles but on older ones it helps idle performance immensely as there is no 'older engine' software update provided by Ford. The wide range is actually PART OF the problem.

You will get NO CODE at that close to the idle speed, the only IAC codes there are are for at end limit either way and the IAC limit on the upside has to cover cold idle as well. You have to look at the IAC pintle itself, these have a seek-to-off position of still open quite a bit meaning there is a lot more shutoff to that direction as well, again meaning no limit code that way either. You gotta look at and understand your parts.

The TPS is not settable at all so why you bring that up I do not know. Mine is modded to be settable but most do not have that, the PCM has an algorithm that takes variance into account anyway. A normal correct TPS will be under one volt regardless of where the idle is set if it is in the right range.
 

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I agree, vacuum leak most likely. Are your long term fuel trims positive, say past 10%, at idle? Try holding revs while monitoring fuel trims, see if they creep back towards 0. That would indicate a vacuum leak. Try dripping / spraying water around the intake connections and listening for vacuum to pull the water in. You'll want to sort the leak out before dialing in your minimum / base idle speed.
 

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AMC, I mentioned TPS signal voltage because it is related to throttle angle. He's changing the closed position throttle angle by turning the stop screw, and thus the signal voltage.

I know how the IAC works. It's a ground-side switched, pulse-width modulated solenoid controlled by the PCM. It's commanded nearly full open when you cycle the key on for second, and then again once cranking is detected. Its duty cycle corresponds with throttle while driving, and at idle it works to hit the commanded RPM by the computer. DSDRPM is the PID if you want to monitor it with live Scan tool data. If you did that, you might see a PCM commanded number below 700, even below 600 at certain times / conditions. On Fords, a duty cycle around 20% is effectively closed. So the 27% we see in the above screenshot makes sense. I think he's got a vacuum leak somewhere.
 

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Discussion Starter #9
I agree, vacuum leak most likely. Are your long term fuel trims positive, say past 10%, at idle? Try holding revs while monitoring fuel trims, see if they creep back towards 0. That would indicate a vacuum leak. Try dripping / spraying water around the intake connections and listening for vacuum to pull the water in. You'll want to sort the leak out before dialing in your minimum / base idle speed.
I'll have to look into the fuel trims later today. I'm assuming I can do that with Forscan (haven't tried before). I thought with vacuum leaks idle speed usually went down? I did a makeshift smoke test before through the valve cover vent but never saw any smoke come out anywhere . I can try the water test. Are there any common leak locations on these SPI engines to check first?

I don't know the cars history but I'm pretty sure at least the head was swapped in the past. I'm wondering if they didn't reassemble something correctly.
 

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I'm not familiar enough with the specifics on that engine but yes generally, it's a MAP system that will idle higher with a leak, not a MAF system. Yes, you can monitor STFT1 and LTFT1 with ForScan.

So, IAC unplugged your idle is 980, and then plugging it in jumped it to 1238? Have you taken the IAC off to inspect clean it? Perhaps it isn't fully closing.
 

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Discussion Starter #11
I'm not familiar enough with the specifics on that engine but yes generally, it's a MAP system that will idle higher with a leak, not a MAF system. Yes, you can monitor STFT1 and LTFT1 with ForScan.

So, IAC unplugged your idle is 980, and then plugging it in jumped it to 1238? Have you taken the IAC off to inspect clean it? Perhaps it isn't fully closing.
The IAC is new but it's an aftermarket part from China so could be defective or not match the vehicle. Dunno. It was different as the connector was straight instead of at a 90 degree angle. Bolted up other than that though.
 

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Discussion Starter #12
The highest the stft I saw at idle was 4.69% but it seems to fluctuate between -0.78 and 1.56% for the most part.

Ltft is 6.25. It has been slowly climbing with the car on for a while.

Also it looks like the ECU is learning the proper idle because it is hovering around 830 now.
 

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Discussion Starter #13
Maybe I didn't have it heated up enough before but I pulled the IAC again and it dropped down to 300rpm and stalled. So I put the screw back in about where it was before and rpms went up to about 600. I stopped there for now. Doesn't look too far off from where its supposed to be I don't think.

I may still have a vacuum leak though, I dunno.
 

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Discussion Starter #14
Went for a drive. Ltft dropped to less than 1. However car was idling at around 2000rpm when I stopped. ECU tried to lower rpms I guess and it just died. Restarted and it's at 700rpm again.

So I guess the IAC is sticking?
 

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How has the IAC been sealed when reinstalled? Could be an issue there. Reusing same gasket there is a mistake.

Pretty much ALL engines that are EFI a vacuum leak at first idles HIGHER until the idle fuel trim runs out, then the idle will drop lower as the engine starves of fuel. Often then the idle will go into the classic seesaw thing or 'rRRr, rRRr, rRRr' behavior as the engine leans then slows to richen then speeds up to lean, etc. Higher idle to get past the 1 volt TPS signals engine is off idle and then the higher speed fuel map interchanges for the pure idle one and engine then idles higher as the higher map has far more fuel allotted to it than the idle map, which hits limit pretty easy.

Went to Rock Auto to look at IACs, the straight one mentioned seems to be geared toward the DOHC motor while the one with connector at 90 degrees is for the SPI, could be an issue there of wrong part.
 

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Discussion Starter #16 (Edited)
It came with a new gasket. I'm not sure if there is anything different about the 2 parts other than the angle of the connector. Not sure how I would find out. I may have saved the old one and could bolt back in (don't even know if it was defective. Replaced it when I had idle issues before).

Also, don't know if this is related or a separate issue but the car has been having issues with moderate/hard acceleration. Usually it's fine but sometimes it seems to choke to the point the engine feels like it's going to stall then suddenly there is a kick and it accelerates normally. Would this be indicative of a vacuum leak as well? Seems to be running lean, though I read it could also be spark blow out. Maybe a clogged cat too though I would think it would be more consistent?

Car has new plugs and wires and new fuel pump and filter. Also refurb fuel injectors (one was dead previously).
 

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If the new gasket got used once and then again it is no longer new.........the IAC connector matters not one whit, what does is the IAC absolute metering and they can change radically and look exactly the same on the outside. Some default to full shut at power off and some stay open in varying amounts due to design. The springs doing that greatly affect the amount of dither the IAC pintle uses to move (and stay) the exact amounts needed to idle correctly. Some use a vacuum assist and lock and some don't as well, need the type matched to the software values there.

'...then suddenly there is a kick and it accelerates normally.'

Normal, they go into open loop past a certain amount of throttle demand (TPS swing) and then the engine gets a sudden rush of power from that, you see it a lot in hot weather and even more with a/c on.
 

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X2, if the gasket was a paper one, then you keep the rubber gasket that was originally used and under the new paper one, it seals better. The paper is flimsy enough that with the rubber shaped o-ring gone it can slip into the groove there to not seal, they often do not have much edge overlap. Leaving the rubber in place as a groove stuffer helps the paper one to seal.

May well have the wrong IAC there.
 

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Discussion Starter #20
I went ahead and bought a new gasket and put back on the old IAC. It seems to work much better. Idle is normal now and it doesn't try to accelerate like it did before with my foot off the gas. Seems like it was the incorrect part and the valve was more open than the computer thought it was.

It still didn't solve my hesitation issue but I'm going to start a new thread because the idle problem has been solved.
 
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