99 Ranger 3.0 with composite intake idle problem

I purchased the truck a couple of months ago wrecked and have spent some time replacing the bed, tailgate, rear window, both bumpers, header panel, grille, and lighting all around.

Truck has a rebuilt motor in it with 20K miles and is super clean. Runs awesome as long as you're not in neutral or between shifts (5 speed) as the truck can't hold an idle. I've even had the truck die when I put it in neutral to coast to a light. I've only driven it maybe 200 miles since I bought it.

Is there anyone else out there with the composite upper mod that's having this problem or could it just be a bad IAC? Any help is greatly appreciated.

P.S. I found a way to fool the PCM into thinking the EGR is still present even though it's not.

Check thoroughly for vacuum leaks. Most likely it's just a bad IAC.

Which method did you use to fool the PCM into thinking the EGR is present?

If you use the accel pedal to just keep it at idle, does it still stall or run rough?

I would pull the IAC off and look at it while having someone else turn the key from off to run (not start). You should be able to see it open each time you turn the key to run. If it does, good, clean it (you tube), if not measure for voltage with key in run. I don't remember what it should be (maybe 5 volts???); but, it has been posted on this forum a number of times so you will be able to find it using the search function. If you get voltage and the IAC did not move, you probably found the problem.

That should eliminate the IAC concern, tell us what you find.

One thing to note is that if a running engine's rpm drops below 500 the computer shuts off the fuel pump.

Froggmann said:

Check thoroughly for vacuum leaks. Most likely it's just a bad IAC.

Click to expand...

I didn't get emails that there were any responses or I'd have gotten back sooner. I ordered a new IAC as I figured the RPMs are dropping so suddenly that it just seems most likely.

Froggmann said:

Which method did you use to fool the PCM into thinking the EGR is present?

Click to expand...

I tried the looping the REF back to the HI and that threw a code within 20 miles for insufficient EGR flow. I then thought that since vacuum is controlled to the EGR by the EGR solenoid and the DPFE voltage can be checked using a vacuum pump on the REF nipple, why not tie manifold vacuum to the EGR solenoid and the other nipple from the EGR solenoid to the REF of the DPFE. Driven it 150 miles and no codes. Sailed right through emissions

Rearanger said:

If you use the accel pedal to just keep it at idle, does it still stall or run rough?

Click to expand...

It runs perfect with any gas pedal at all. I tried bumping up the idle screw on the TB, but it still sometimes dies when I shift and RPMs are going from 3500 to 500 in 1-2 seconds, it just stalls.

enjr44 said:

I would pull the IAC off and look at it while having someone else turn the key from off to run (not start). You should be able to see it open each time you turn the key to run. If it does, good, clean it (you tube), if not measure for voltage with key in run. I don't remember what it should be (maybe 5 volts???); but, it has been posted on this forum a number of times so you will be able to find it using the search function. If you get voltage and the IAC did not move, you probably found the problem.

Click to expand...

I actually pulled it off the other day and saw that it was very dirty... like I've never seen on any vehicle I've owned. I cleaned it out with TB cleaner and noticed that it wouldn't completely close on its own. I had to give it a slight push from a small screwdriver. I just figured I'd replace it and forgo a bunch of testing.

enjr44 said:

One thing to note is that if a running engine's rpm drops below 500 the computer shuts off the fuel pump.

Click to expand...

Didn't know that. Probably what's happening when it stalls. I'll post up if the IAC does the trick. Thanks guys.

Changed out the IAC yesterday and drove it around a bit. Doesn't appear to have done any good at all. Here are some specifics about the issue:

* Between shifts, the idle usually drops fairly quickly to around 1100RPM and then transitions down to around 900RPM. Sometimes it bounces from 900-500RPM up and down 2-3 times. Other times when I press in the clutch and let off the gas, the RPMs drop all the way to 900 and immediately surge or bounce from 500-900RPM 2-3 times. Then, sometimes (rarely) it acts completely normal.
* Idles fine as long as you're not just coming out of a higher RPM.
* Actually only stalled 3 times in 200+ miles, but it's annoying. Stalling may be related to AC clutch kicking on when RPMs already dropping from 900.

Would it make sense for me to erase PCM memory? Could the IAC actually be the fix, but I need the PCM reset?

So nobody else has had this problem with the composite intake swap? Had I done this myself, I'd feel a lot better about it, but it was already completed when I'd bought it.

The TPS tells the computer when throttle closed. Wouldn't hurt to check adjustment of TPS. You may also have some crud in the throttle where the throttle plate closes, check there and clean.

I've noticed that that when on idle and moving the idle remains high(er) until speed almost zero. Speed sensor must be involved.

Rangstang said:

So nobody else has had this problem with the composite intake swap? Had I done this myself, I'd feel a lot better about it, but it was already completed when I'd bought it.

Click to expand...

The only issue I had with the composite swap was a hanging idle between gears when accelerating. Turned out to be a TPS adjustment, had it set at .95v, changed it to .85v and it cured the problem. Haven't had an issue since, the intake has been on my truck for 3-4 years.

Froggmann said:

The only issue I had with the composite swap was a hanging idle between gears when accelerating. Turned out to be a TPS adjustment, had it set at .95v, changed it to .85v and it cured the problem. Haven't had an issue since, the intake has been on my truck for 3-4 years.

Click to expand...

Okay, so this definitely means I've got a problem. Thanks, that was my biggest question.

Rearanger said:

The TPS tells the computer when throttle closed. Wouldn't hurt to check adjustment of TPS. You may also have some crud in the throttle where the throttle plate closes, check there and clean.

Click to expand...

I'll look into the adjustment and see if that's the issue. Already cleaned the TB thoroughly a couple of weeks ago.

Rearanger said:

I've noticed that that when on idle and moving the idle remains high(er) until speed almost zero. Speed sensor must be involved.

Click to expand...

Is this something you've experienced?

Idle relearn is very simple procedure:

Get the truck up to full operating temperature, shut off engine.
Disconnect battery negative cable and touch it to the B+ that is still connected.
That will erase all of the non-volitile memory.

Reconnect the battery, start the truck. Do not touch the gas pedal.
Idle for 4 minutes in each of the following conditions:

Neutral, foot on brake (Park for an automatic)
Neutral, foot on brake, AC on. If you have a stick shift, you are DONE after this step.

Drive, foot on brake
Drive, foot on brake, AC On.

At that point the idle should be high, like over 800, close to 900.
As you continue to drive the truck, it should continue to learn its idle strategy and eventually slow to 700-ish for a stick shift, 800-ish for an automatic in Drive.

The PCM does indeed use the speedometer signal to control the idle. It props up the idle during shifts on a stick shift truck. As you pass below 5mph, the idle should drop to 700 if you are coasting in Neutral or have the clutch disengaged.
Since yours is not doing this, you either have blocked up ports in the intake (remove the IAC again and dig the carbon out of those ports) or the speed signal is not getting to the PCM pin 58 on the GY/BK wire from the GEM (2wd) or 4WABS module (4wd).

Many of us older stick shift drivers don't like the way Ford props up the rpms for shifts and many (Mustangs) have taken steps to eliminate this "feature". Some have cut themself a new IAC gasket with much smaller holes in the gasket to restrict how much the IAC can control the idle speed. Others have put in a switch or cut that GY/BK wire to take the speed signal away from the pcm.

The perceived advantage is that it gives you back old-school engine braking when you let off the gas.

If you end up figuring its an electrical problem and want the schematics, send me a PM with your email address and I'll send them to you. No email address, no files. You'd be surprised how many ask me to send them and don't include the essential email address.

Earl43P said:

Idle relearn is very simple procedure:

Get the truck up to full operating temperature, shut off engine.
Disconnect battery negative cable and touch it to the B+ that is still connected.
That will erase all of the non-volitile memory.

Reconnect the battery, start the truck. Do not touch the gas pedal.
Idle for 4 minutes in each of the following conditions:

Neutral, foot on brake (Park for an automatic)
Neutral, foot on brake, AC on. If you have a stick shift, you are DONE after this step.

Click to expand...

Thanks for all the helpful info Earl. I don't get email notifications when there are updates, so I didn't set this until this morning. I've got a stick, so this will be the end of the relearn for me.

If I need schematics, I'll hit you up, thanks for the offer.

Byron