Problems with idle after H/C/I, any suggestions.

You're on the right track.

1. It may be that the idle air bypass valve is a bit gummed up. Replace it with a new one, try to clean it, or there is a idle air adjustment plate that can be installed on the IAB. You can get one from Ford or any of the major performance warehouses.

2. It is OK, and often preferred, to have the warm idle set at 900-1000 after H/C/I swaps. Sometimes, it's the only way to smooth things out. Mine sits at 900-950...and that's after custom tuning and having an idle air adjustment plate installed. Depending upon your cam, the valve timing may be altered enough that it simply won't run at 600-700 RPM any longer...it's OK, no worries.

3. The stock MAF housing and stock TB/EGR plate will not so much be a problem at idle, but at higher RPM when the air flow demand is much higher.

You may be stuck with adjusting the idle adjustment screw on your throttle body, for now, but this obviously effects your TPS settings. I think I would order a FMS 65mm ID TB/EGR. The FMS units come with a brand new IAB. If you go aftermarket, then you have to purchase the IAB separately. Then, if that doesn't settle things down, you may need the idle air adjustment plate...which, BTW, was designed specifically because of cam swaps. It even says so on the packaging.

After that, your 53mm ID MAF is obviously a restriction at WOT. I'd switch it out for a 70-73mm. If you go too large, resonance issues come into play and the idle and drivability start to get a little quirky. With MAF units, bigger is not better. It must be appropriately sized for it's application. For more info, just click on to the Pro-M site and read their troubleshooting guide.

Had the same problem when I did my swap.. Bought the idle adjusting plate and it fix the problem, it's like a $20 or so. I bought mine from www.mustangsunlimited.com

Definetly clean out the IAB. Remove the solenoid and generously spray gum out all in the valve. It should then be as good as new.
My car with H/I/SC idles steady at 700.

i knwo it sounds stupid, but why can't you just adjust the screw on the TB? or does that throw a whole bunch of other things off as well? I also have the same prob, i just added the 76mm MAFS, 30lbinjectors, and a adj FPR. I'm also not sure as to whree to set the fuel pressure, its at like 35 right now and it runs way rich. the air fuel also dosn't swing like it used to b4 the injectors, and i get a 3-400rpm surge it goes from like 500rpm to 1000 and just goes back and forth with the airfuel on the rich side. i'm not sure as to what to do. just play with stuff????

There's not a one-size-fits-all solution to idle issues when modding these motors. It's probably the single biggest headache faced by those of us playing with them. At the heart of the problem is that the designers of the system never intended the idle speed to be adjustable. The screw referred to in the post is actually a throttle stop screw, not an idle speed adjustment screw. It's purpose originally is simply to keep the throttle blade from closing too far and binding in the housing. The computer controls the idle speed with the iab solenoid and by altering timing. Part of the reason that surge is an issue is because for all our attempts to raise idle after mods are added, the computer's trying to get it back down to about 675 rpm - preset in the ecu. Surge is the result of that ongoing battle. Theoretically, if you open the throttle blade a bit by turning the throttle stop screw, once the car is restarted once (it'll take a new tps base reading each time the car is started) all that will happen is the computer will sense the higher idle rpm, and close the iab solenoid a bit to bring the idle back to where it was. There are procedures out there (disconnect iab, turn screw, turn off car, reset tps, plug in iab, disconnect battery to clear memory, face Mecca and pray, etc., etc.) that work in some cases. Some folks have had the idle plate (which works EXACTLY like a MANUAL iab solenoid) help them; some it didn't help at all. Every circumstance is different - and compounded by the fact that when h/c/i changes are made, there is almost always a vacuum leak of some sort that is compounding the idle surge/roughness issue.

From my perspective, first step is to be absolutely certain there are no vacuum leaks --- and that takes some doing. The biggest culprits are old vacuum lines that people re-use. Second biggest culprit is brittle, hard pcv grommets that don't seal around the pcv valve the way they should. If you can easily pull you pcv valve in and out of the grommet (I'm not talking about reaching it - that's always difficult! ), then you probably have a leak of some magnitude. Once you're certain unmetered air is not entering the manifold, then you can start with the idle-resetting procedures. And there's just no guarantee it's gonna work on everycar. I chased it for six months on mine - finally, we reset the idle speed in the computer with a chip - and that solved it first time we cranked it up after that. As odd as it sounds, some computers 'fight' a new idle speed more than others; while some seem to allow it as part of their adaptive strategy programming. Don't know why - but it seems to work that way. Good luck with it Astro.....

By the way - the idle air bypass plate was originally a Ford re-call part. They used them to help restore idle quality to engines that had gummed up throttle bodies and iab solenoids - they weren't maintaining their idle quality/emissions for the 5 years/100,000 miles (whatever the spec is?) that was required. Ford found that by manually bypassing a bit of air around the throttle plate, even a gummed up throttle body/iab solenoid could be made to produce a reasonable idle. The plate cost them about a $1, and took a good mechanic about 3 minutes to install. That was a WAY cheaper fix than actually removing/cleaning/replacing throttle bodies and iab solenoids. Others are making it now too.

RyanSG said:

i knwo it sounds stupid, but why can't you just adjust the screw on the TB? or does that throw a whole bunch of other things off as well? I also have the same prob, i just added the 76mm MAFS, 30lbinjectors, and a adj FPR. I'm also not sure as to whree to set the fuel pressure, its at like 35 right now and it runs way rich. the air fuel also dosn't swing like it used to b4 the injectors, and i get a 3-400rpm surge it goes from like 500rpm to 1000 and just goes back and forth with the airfuel on the rich side. i'm not sure as to what to do. just play with stuff????

Click to expand...

A couple of things you could try:

Simply adjusting the screw on the TB does allow more air into the system and raise the idle, BUT it throws off the TPS settings which should be around 0.96-0.99v when the TB is in a closed position. The TPS voltage can significantly effect idle and drivability. That said, one should try to fix the problem at hand, so that the TB can be in the closed position at idle and have the proper TPS voltage.

One of the main reasons for surging is that it can't get enough air with the TB in the closed position...especially after H/C/I swaps. Often times it is that the IAB isn't allowing enough air into the system, whether it isn't funtioning properly, it's gummed up with crud, OR you just need an idle air adjustment plate installed between your IAB and TB. The later, probably your best bet assuming your IAB is working properly. This situation is typically most prevalent during cold-start/idle.

Once warmed up, assuming all your sensors (ECT, ACT, EGR, O2 and so on) and your computer is working correctly, the computer will adjust the fuel injector duty cycle up and down to maintain the proper air/fuel ratio. So, often times fuel pressure settings have little to do with air/fuel ratio at warm idle, unless the setting is way too low (lean) or the injectors are too large (rich). Fuel pressure setting is however, critical at WOT, especially when tuning for maximum power. If the engine is running a little rich during cold-idle, it is supposed to (within reason). If it is running rich during warm idle, then it MAY be you are using too large of an injector. However, before swapping injectors, make sure everything else is working properly.

The 76mm MAF. If it is a C&L unit (I am running the same), then I have found that these sensors are really sensitive to resonance issues and need to be protected from fan wash. I created a sheet aluminum piece that covers my airfilter and MAF. It was a significant difference and really smoothed out the idle and cruise operations.

Another thing. If you are using a cone-style air filter (K&N, or the like) you have make sure that the air filter outlet is at least 76mm ID, as well. If you have somehow put on a filter that was designed for a stock 5.0L, it has a 53mm ID outlet and may be creating flow eddies as the air moves from a small conduit to a large conduit...which the MAF senses and creates some erratic behavior with the engine. I made this mistake, as well. I had to take a razorblade knife to the end of my filter to make it fit over my MAF. Anderson Ford Motorsport sells filters with larger openings, as well.

In the end, custom computer tuning is something that I highly recommend for any engine that has received significant mods. Make sure that cold-idle, cold-start, warm-idle, cruise, WOT, etc. operations get addressed with the tuning. They'll have it on the dyno several times with a wide-band O2 sensor installed just past the headers and a laptop plugged into your computer. Plan on the tuner having it for at least a few days to work out any "bugs" and allow for the computer to learn the new settings before you pick it up.

Just me....

ok guys, i'm gunna check out some of these issues in a few min, gunna print all these out and start checken everything. I'm going ot get the car dyno tuned hopefully in the next week. So i'm not sure if i shoudl even care about it as long as the car is running till i let the dyno guy play with it (even though i will anyway b/c i hate having my beast misbehaving lol) We'll see how it goes, i'll relay the info as i get it (good or bad either way) Thx guys your def helpen me sort this out!

well i got the prob fixed!!!! it ended up to be the timming!! i had to retard the timming by a few degrees. the idle smoothed out, the air fuel was perfect, and it runs liek a mo-fo!. I also did what you guys said as well b4 i set the TB back to what it shuld be etc. which i'm sure helped a bit def. so it's all good now. so if all else fails play with the timming a bit!! ANyways, thx for all of the info guys!

lol true true. but it is def worth a shot if your outa ideas and things to try. worked on mine but every cars different.