Idle adjustment on an 84 CFI setup

[Matt J]

After about a year of chasing faulty sensors and vacuum leaks, all I have left is to replace my throttle position sensor which has been showing up on my diagnostic tests since I bought the car. I back-probed the leads on it and the voltage was all over the place, and even when the car is idling when I jiggle the wires on it, I can hear it clicking and it affects the engine idle, well in any case it needs to be replaced and I have one coming. We found a huge vacuum leak in the cruise control module, so that's been disconnected and plugged until I have the time to fix it (why would anyone put that in behind the fender, anyway). My question is about the idle on the car, it's really low now that the final big air leak is fixed. When stopped at a light in drive, it can idle around 200-250 RPM, and can even stall once in a while. I'm thinking that the TPS might help with this, though I'm not sure if it has anything to do with controlling the idle on the car. I've looked through a number of references and can't see where there's an idle adjustment on the stock 84 CFI. The TPS isn't adjustable on that year, I did read in my Haynes manual something about if someone adjusted the idle screw, it might affect the TPS functioning properly. But that guide covers all the years of the fox bodies, and the TPS is slotted and adjustable in later years.

Once I get the TPS in and working correctly, if the idle is still too low, is there an idle adjustment on the stock 1984 CFI, or is it all computer controlled?

[Matt J]

Anyone have any experience with this?

[JACook]

The TPS doesn't affect your idle speed, but on a CFI engine, a bad TPS will often make the idle hunt.

If you adjust the idle speed on a CFI car by more than 50 RPM, the AOD Throttle Valve adjustment
should be redone.

The CFI idle adjustment is done by moving the throttle positioner. Loosen the lock screw, turn the
adjustment lead screw, tighten the lock screw. Pretty simple.

The actual -procedure- for a CFI 5.0 is a bit more complicated.

• Set the parking brake
• Bring the engine up to operating temperature
• A/C-Heat selector Off.
• Shut the engine off, then restart and immediately bring it to 2000 RPM and hold it there for 60
  seconds in Neutral, then let it idle for 15 seconds
• Without restarting the engine, bring it back to 2000 RPM for more than 10 seconds in Neutral
• Put the transmission in Reverse, then check/adjust the idle speed within 60 seconds

If the idle speed is too low to get through the procedure, shut down the engine and turn the adjustment
screw one full turn, then repeat the procedure.

[Mikestang]

Have you verified that the DC motor for IAC control works? Should be a 4 wire connector on the side of the CFI unit. I have seen these motors go bad. Usually I manually command them out to seat the pintle to obtain a "min air" setting. (that is done with the IAC unplugged) Then set the base screw to around 500rpm, sometime you have to play with that speed, maybe 550 or so. At that point if the IAC DC motor is working and the PCM is working it will move the IAC motor to where idle should be, usually around 800 or so. If you need more info let me know. I do not remember the wire colors for the motor off the top of my head, you would apply fused power to ISC + and ISC - this is how you manually move the motor. I thought there were minor differences in the CFI systems, thought there was a EEC3 and EEC4 version? Not sure how you would verify that? Hope I did not just confuse you more, I have only worked on a handful of those.

[JACook]

I guess I should have asked whether this is a 5.0 CFI or 3.8. The 5.0 does not use a DC idle speed
motor like the 3.8 does, so the failures common to the 3.8, like the idle tracking switch, do not apply.

The CFI 5.0 actually controls idle speed by varying the ignition timing. It also has a vacuum operated
throttle modulator that can kick the idle speed up a notch when needed, such as when the engine is
not up to operating temperature, or when the A/C compressor engages.

[brianj]

It is a completely stock 5.0 CFI auto. It should be a carb'ed 5.0 5-speed, but he is one of "those" guys- it is staying stock. Any ideas about the idle?

[Mikestang]

I guess I should have asked whether this is a 5.0 CFI or 3.8. The 5.0 does not use a DC idle speed
motor like the 3.8 does, so the failures common to the 3.8, like the idle tracking switch, do not apply.

Good call

[Matt J]

It is a completely stock 5.0 CFI auto. It should be a carb'ed 5.0 5-speed, but he is one of "those" guys- it is staying stock. Any ideas about the idle?

Hey, I'm happy with my 16 second 1/4 mile, or whatever it is! I think Jeff's instruction on getting the computer set will probably be helpful, I know the EEC4 computer has a "learning period" and this will skip that. Or blow it up.

I'll get the new TPS in there and see if it's even an issue. I just know I was looking for an idle screw on the thing someplace, and there was none to be found...Thanks guys!

[JACook]

To be sure, the TPS voltage jumping around is definitely an issue.

And yes, the complicated procedure is to "teach" the EEC-IV what it's target idle speed is supposed to
be. It sounds a lot more difficult than it is, but even after doing it many times, I still pull out the book.

Since you already know your idle is too low, I would probably start by just adjusting it without all the
learning stuff, and replace the TPS, and see if you get a stable idle.

[Matt J]

In retrospect, it would have been helpful for me to mention it has cruise control...I figured out that I have to adjust the position of the cruise control module (or actuator, or whatever it's called) in order to adjust the base idle position. Brian also suggested to me that I unplug the battery for a while...you know the instructions in the Haynes manual told me to disconnect the negative terminal on the battery before replacing the TPS (and pretty much everything else). I assumed it was just a safety thing, but you know that computer really needs a reset sometimes, and that kind of does it. In any case, I adjusted the cruise module a little to kick up the base idle a little, but it was still hunting a little, bouncing up between about 400 RPM to 1,000. After letting it sitting unplugged for a few hours I hooked it back up and it's running a lot better now. Might be coincidence, but in any case it's running better now.

[JACook]

Good to see you got the idle under control, but I'm having a hard time wrapping my head around
what cruise control has to do with this. It shouldn't matter. But if what you adjusted looks something
like this:

Then it makes perfect sense.

[Matt J]

Yeah, that's it, isn't that the cruise adjuster-thingy?

[JACook]

Nope, has absolutely nothing to do with cruise control. It's called a vacuum operated throttle
modulator, which is just a fancy name for a kicker solenoid with a vacuum line instead of wires.
The ECU commands vacuum to the VOTM when it wants to raise the idle speed, such as during
warm-up before the engine goes into closed-loop, or when the A/C compressor is engaged.

[Matt J]

Ah. Well, I learned something new today, thanks! I'm still having some issues with the idle...when the car is cold it starts and idles fine, but once it's heated up, the idle is still too low, to the point where it will stall if the engine is revved and then the foot taken completely off the gas, the idle will drop almost to 0, then will sometimes catch and bounce back up to around 500 RPM. When I stop and put it in neutral or park, it will start to "hunt" from around 250 RPM to about 1,000 rpm. It will just bounce up and then kick back down. It might even stall sometimes. I have to give it a little gas to get it re-started, I shouldn't need to do that it's fuel injected and never needed it before.

I've replaced the TPS, PCV, EGR position sensor, all vacuum lines, the car has been tuned up. I haven't had a chance to put the thing on the computer diagnostic since I installed the new TPS, and I didn't back-probe the new sensor to be sure it was in the correct voltage range. Since we blocked off the vacuum line to the cruise control module (the real one in the fender well, it had a major vacuum leak), the idle is really low. Could even be timing, if the thing was leaking a long time ago, they might have changed the timing to compensate for it. Something else I still need to check. The car runs great when under power, just an issue at idle.

[eight666lx]

I know it sounds much too simple to be the problem, but i had the exact same problems with idling in my 86 cfi 3.8. it would stall, go down to zero then catch and go up to 1000, hunt in neutral or park, and all hell broke loose with the A/C on... it turned out that tightening the vacuum lines helped alot, things never became perfect but something so easily overlooked as a loose hose (especially if they are new/have been played with recently) can be at fault.

[JACook]

Make sure that VOTM operates when vacuum is applied. Coming off the throttle is one of the
conditions where it will normally kick the idle up for a couple seconds. You may need a new
one, or the vacuum solenoid that feeds it may have failed.

[Sally]

I also have an '84 CFI setup and I too have spent about a year chasing faulty sensors and vacuum leaks with the exact same idling problem you are experiencing. I've been able to get my "warm" idle to a fairly steady 550 RPM now, versus the 200 RPM plus fluctuations I was experiencing after a nightmare of a time troubleshooting and spending a small fortune replacing parts that probably didn't need to be replaced, just chalk it up to a learning experience. Mine would stall after it warmed up and came back to an idle (kind of sucked at busy intersections lol). I found a tiny crack in the ground wire that goes from the coil to the distributor (into the module), replaced it and it was like night and day.
My advice:
1. Make sure all of your ground wires and cables are new and working. (Check wire from coil to distributor)
2. Finally, there are two fuel pumps: one in the tank that is high pressure, and one in the frame that is low pressure; change the filter in the low pressure if you haven't already.
Everyday seems like a challenge with this classic car but she is a mean, lean beauty so it is worth it. Hope this helps and good luck.

[Matt J]

I'm having a heck of a time finding one of those anywhere online, I saw your photo came from RockAuto, but can't locate it there. Does it go by any other names?

Make sure that VOTM operates when vacuum is applied. Coming off the throttle is one of the
conditions where it will normally kick the idle up for a couple seconds. You may need a new
one, or the vacuum solenoid that feeds it may have failed.

I just tested the unit by putting a little vacuum on it (no snide comments anyone ), and it did operate. I started the engine and could feel some vacuum coming from the line, including when I revved the engine, so I think it works okay. That said, it tried it hooked up, and it worked, but then after it was hot, it stopped. I also noticed the #1 solenoid (the one furthest to the front of the engine bay) that controls the EGR vent is clicking away so much that it actually sounds like a bad lifter (probably 3-4 times a second). I noticed when that was happening, the VOTM stopped extending when I revved the engine. It's possible it's using up too much vacuum, or something. Not sure what would make that soleniod freak out like that, or if it's supposed to do that. I tried adjusting the base idle up again, it seemed to work , but once the car got hot the idle dropped way down again. I actually had to restart the car 4 times to just park it, it's becoming undriveable at idle speeds. I think I'm just going to have to start from zero and go through it all, vacuum, timing, fuel, electric, etc. It's really frustrating, the car runs great anytime but when the foot is off the gas.

I'm curious, these problems started when we disconnected the cruise module as we could hear a leak in the fender well (and plugged off the vacuum line of course). It fixed some of the rough running issues I'd been having to that point, but the idle went nuts after that. I'd guess it's leaked for a long time as the cruise didn't work when I bought it, so it's possible the previous owner had adjusted lots of things around it to overcome the problems associated with the vac leak, which are now causing trouble now that it's blocked off. Is there anything else plugged in to the cruise module that affects the idle? I intend to fix the cruise when I have the time, but needless to say I'll move those plans up if this is what's causing the trouble.

[JACook]

The EGR supply and vent solenoids are supposed to rattle a bit, it's the main reason the solenoid bracket
is on rubber mounts. The EGR valve doesn't just open and close, it's got a position sensor, and the ECU
"dithers" the supply and vent solenoids to control it's position.

I think it's probably normal that the VOTM doesn't operate once the engine has gone closed-loop, but there's
an easy way to tell if the solenoids have enough vacuum to operate. Just temporarily tee a vacuum gauge
into the line to the reservoir.

When my VOTM failed, I bought a new Motorcraft unit from eBay, but Rock Auto has one left, if you think
you might need a new one. Probably not though, if yours holds vacuum.

You have to adjust base idle after the engine is warmed up, and the VOTM should -not- be extended.

[Matt J]

Thanks, again, Jeff. Is there anything you don't know about these things? Just curious, how much vacuum should I be seeing?

I might need a new VOTM, as mine operates when I draw down on it with a little vacuum, but it doesn't seem to hold it for all that long. It might have a small leak, the thing is no doubt really old and I've had to replace the other rubber vacuum parts on the car. I feel like a dope, but I can't find the thing on Rock Auto at all...what do you use as your search criteria on the site? There's nothing there for Mustang 5.0 for 83-85, I just can't find it anywhere. Might be under another car or engine option, I suppose.

Even with the VOTM working perfectly, still not sure what's making the idle hunt. It comes and goes, too. I drove it today, worked great (it's getting chilly here, it was only about 60 degrees out), but then I approached a stop sign, and noticed the idle was hunting, surging the car forward then letting off, and then stalling. Drove it a little more, and it idled perfectly. I revved the engine a few times to see if it would kick down to a low idle, it held steady at 750 RPM. Got me a little confused, though I haven't had the time to work on it. I think the first thing I need to do is to verify the timing is set right, and that the timing advance is working correctly.

I had one other question for clarification, you mentioned how to set the base idle before involving a set screw and an adjustment, and I've been adjusting it by moving the VOTM with its adjustment screw (and nut that holds it in place). Am I adjusting the right spot for that? I'm trying my best to work with this setup, if it was a carb I'd have fixed it all months ago...this is all new to me so I appreciate your patience and good advice!

[JACook]

Well, apparently I didn't know enough to give you the actual part number for the VOTM... Motorcraft CD-69.
Just put that in their part number search box. You can also find these at RockAuto and elsewhere by searching
for E3VY9S520A. Other numbers are Standard D5131, and Airtex 1D1017.


The VOTM is given full manifold vacuum when the solenoid is picked. If you manually apply vacuum to it, it
should not leak down. How you're adjusting the base idle is how it's done, at least as far as the mechanical
actions. Loosen the lock screw, then turn the lead screw, then lock it back down.

On my '85 Vert, the CFI system is kinda picky about fuel pressure and ignition timing. Make sure your crank
damper ring hasn't moved, or you might not be setting the timing where you think you are. And of course,
make sure the SPOUT connector is unplugged when you check/set the timing. Fuel pressure should be 39PSI.

The other thing that I found on my '85 Vert was the MAP sensor was leaking, so I tried putting in a used one
(baro sensor) off a '93. It worked better, but when I put the proper one for an '85 in it, there was definitely
a difference. I believe the MAP sensor for the CFI cars is the same as what was used on the speed-density
SEFI cars. Mine is labeled with engineering number E6EF-9F479-A2A, Motorcraft p/n DY-503. If you need one,
they can be had pretty cheap on eBay right now. Make sure the vacuum hose to the MAP sensor is not kinked,
and does not tee into anything else.

[Matt J]

Thanks a million! It looks like "dashpot" is the magic word, now I can find it all over the place. I have a few things to check on before replacing that, but if it does have a little leak, it's just one more place in the engine that vacuum is being lost and affecting things. Thanks for all your help, I hope to get this figured out soon!

[brianj]

Edelbrock 1405. I even have an intake for you! Just kidding. I wish I could help more but CFI is beyond me.

[Matt J]

If the whole thing didn't rely so much on vacuum operated mechanicals (and all the hoses that go along with them) it would actually be pretty easy to work on. Everything went to electrical connections within a few years, but these things kind of broke the trail for the wires instead of hoses system we use today. It's just a small leak on the other side of the engine bay (or behind the fender well as we ran into on mine) will create a problem someplace else. Kind of hard to find the issue. I know once it's 100% it's pretty fool proof, it just sat for so long everything needs going through. You mentioned to me a few weeks ago to check in the distributor as well, the idle advance might not be working correctly either. We'll get it figured out.

[JACook]

The distributor used on the CFI engines has no advance capabilities of it's own. Spark timing is all
under control of the EEC-IV module.