Fixed Idle Problem, But Now Stalling At Abrupt Stops?

dz01

Member
Mar 31, 2005
274
10
19
Massachusetts
I finally solved my hanging idle problem, but looks like I created another.

Last time I smoked my system I found my throttle shaft (bottom) and EGR leaking.

Rather than screw with a bone yard TB, I picked up a new BBK 65mm TB and spacer. New TPS included was already set, but I checked it 4 times as I set the idle. Before I replaced the EGR I wanted to see how a new TB ran. Test drive was good, but car idled too high. I unplugged the IAC and set the idle at 600. Car seemed to run pretty good except abrupt stopping or if the car was under a load (turning wheel at low speed) would almost stall the car out, then my idle would dip almost to the point of stalling and rise about 3-4 times. For a few seconds, car seemed to struggle to keep running, then back to running fine. I did notice the car seemed to idle low after driving for 15 minutes with my new setup. Even though I set the idle by the book, I turned up the idle screw 1/4 turn (still might need to turn it up a little).

At this point I had not replaced the EGR, but have since installed a new one- no change

My IAC is not new, but clean and I would think if it were junk I would have noticed issues with the old TB. I do have a new motocraft IAC in the box (funny it doesn't say Ford on it).

Any ideas? The only thing different from "no stall problem" to "stall problem" was my TB and spacer. The new EGR didn't change anything.

-Is my idle too low? I could see this possibly contributing to this problem.

-Is this a symptom of an IAC that I might not have noticed before b/c my idle would hang then come down to idle? Is it the IAC that increased RPM slightly as you slow down so you don't stall out?

I have not pulled the codes yet, but will probably do that next.
 
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If your IAC was the issue, you would have this problem when you started the car initially. It sounds like your idle is set too low. You want somewhere around 750 - 800. Do a base idle relearn at or around 750 and see how it does. I know not all set ups are the same and what works for mine may not work for yours, but my idle is set to about 650 - 700 with no accessories on. I run lower with the a/c on, and there are times where it will dip down pretty low on deceleration. But I like how I sound at idle with my cam.
 
I would check codes first, as well as check for vacuum leaks. It's quite possible you inadvertently damaged or removed a vacuum line when you were making your modification. I'd give the known vacuum areas a few shots of brake cleaner and see if there's a change in the idle.

After that's done, get back to us.
 
If your IAC was the issue, you would have this problem when you started the car initially. It sounds like your idle is set too low. You want somewhere around 750 - 800. Do a base idle relearn at or around 750 and see how it does. I know not all set ups are the same and what works for mine may not work for yours, but my idle is set to about 650 - 700 with no accessories on. I run lower with the a/c on, and there are times where it will dip down pretty low on deceleration. But I like how I sound at idle with my cam.

Thanks. I'll try to set the base idle a little higher. Question, do I need to disconnect the IAC and pull the neg cable every time? Seems easier to just go a 1/4 at a time whether the cars running or off.
 
I would check codes first, as well as check for vacuum leaks. It's quite possible you inadvertently damaged or removed a vacuum line when you were making your modification. I'd give the known vacuum areas a few shots of brake cleaner and see if there's a change in the idle.

After that's done, get back to us.

No codes with key off. Have to wait to fire the car up until tomorrow to run codes with car on.

Vacuum leaks are always a possibility, but I was pretty careful especially since I've been chasing vacuum for months now. I even torqued the TB bolts to the correct specs and used all brand new gaskets, re-tightened all hose clamps on air intake and trippled checked all other bolts on sensors.

I'll report back once I bump my idle up a tad and run codes with car on.
 
You may already have this, but just in case you don't, here it is...

Setting the base idle speed:
First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. If you have a wild cam, you may have to raise this figure 100-150 RPM or so. Then the electrical signal through the IAC can vary the airflow through it under computer control. Remember that the IAC can only add air to increase the base idle speed set by the mechanical adjustment. The 600 RPM base idle speed is what you have after the mechanical adjustment. The IAC increases that speed by supplying more air under computer control to raise the RPM’s to 650-725 RPM’s. This figure will increase if you have a wild cam, and may end up between 800-950 RPM

Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

This isn't the method Ford uses, but it does work. Do not attempt to set the idle speed until you have fixed all the codes and are sure that there are no vacuum leaks.

Disconnect the battery negative terminal and turn the headlights on. Leave the battery negative terminal disconnected for 5 minutes or so. Then turn the headlights off and reconnect the battery. This erases the computer settings that may affect idle performance.

Warm the engine up to operating temperature, place the transmission in neutral, and set the parking brake. Turn off lights, A/C, all unnecessary electrical loads. Disconnect the IAC electrical connector. Remove the SPOUT plug. This will lock the ignition timing so that the computer won't change the spark advance, which changes the idle speed. Note the engine RPM: use the mechanical adjustment screw under the throttle body to raise or lower the RPM until you get the 600 RPM mark +/- 25 RPM. A wild cam may make it necessary to increase the 600 RPM figure to 700 RPM or possibly a little more to get a stable idle speed.
Changing the mechanical adjustment changes the TPS, so you will need to set it.

When you are satisfied with the results, turn off the engine, and re-install the SPOUT and reconnect the IAC. The engine should idle with the range of 650-750 RPM without the A/C on or extra electrical loads. A wild cam may make this figure somewhat higher.
 
You may already have this, but just in case you don't, here it is...

Setting the base idle speed:
First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. If you have a wild cam, you may have to raise this figure 100-150 RPM or so. Then the electrical signal through the IAC can vary the airflow through it under computer control. Remember that the IAC can only add air to increase the base idle speed set by the mechanical adjustment. The 600 RPM base idle speed is what you have after the mechanical adjustment. The IAC increases that speed by supplying more air under computer control to raise the RPM’s to 650-725 RPM’s. This figure will increase if you have a wild cam, and may end up between 800-950 RPM

Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

This isn't the method Ford uses, but it does work. Do not attempt to set the idle speed until you have fixed all the codes and are sure that there are no vacuum leaks.

Disconnect the battery negative terminal and turn the headlights on. Leave the battery negative terminal disconnected for 5 minutes or so. Then turn the headlights off and reconnect the battery. This erases the computer settings that may affect idle performance.

Warm the engine up to operating temperature, place the transmission in neutral, and set the parking brake. Turn off lights, A/C, all unnecessary electrical loads. Disconnect the IAC electrical connector. Remove the SPOUT plug. This will lock the ignition timing so that the computer won't change the spark advance, which changes the idle speed. Note the engine RPM: use the mechanical adjustment screw under the throttle body to raise or lower the RPM until you get the 600 RPM mark +/- 25 RPM. A wild cam may make it necessary to increase the 600 RPM figure to 700 RPM or possibly a little more to get a stable idle speed.
Changing the mechanical adjustment changes the TPS, so you will need to set it.

When you are satisfied with the results, turn off the engine, and re-install the SPOUT and reconnect the IAC. The engine should idle with the range of 650-750 RPM without the A/C on or extra electrical loads. A wild cam may make this figure somewhat higher.

Yes, thank you. I just thought I could "cheat" a little and tweak the idle screw without having to follow the whole process. Especially since I only need to make minor adjustments to increase the idle. I'll follow the rules:) Plan to run codes with engine on today (God help me if I'm still throwing 41 and 91 after replacing my cracked intake plenum, installing a new TB/spacer and installing a new EGR- all of the areas that I found to be sucking air), then adjust idle a little higher the proper way and see where I'm at. I've heard if idle too low car stalls coming to abrupt stop like mine does, too high and the hanging idle symptom comes back. Sounds like there's one perfect spot that I need to find.
 
Yes, thank you. I just thought I could "cheat" a little and tweak the idle screw without having to follow the whole process. Especially since I only need to make minor adjustments to increase the idle.
You can, as long as you stay within the TPS acceptable range of adjustment (somewhere in the .80-1.05V range). You must however turn the key off and restart the car everytime you make a changes to the idle screw position, as the TPS is zero'd and reset by the computer after each start up.
 
Did some more testing today...not really sure where this leaves me...but it's not what I wanted to report back...

- checked codes with car running. Pulling 41 and 91 still (both O2s lean)! (I've been chasing these two codes for 7 months off and on- new O2s, tightened ground bolt on back of head, fixed all vacuum leaks)...lost on this one

- Raised idle slightly. With engine warm (ran for 15 mins) my idle was about 850. Car actually ran great at least initially. No stalling at all with abrupt stopping or turning wheel. Idle hang minimal at best which I could live with. Drove car about 10 mins (definitely at operating temp by this point). TPS sensor at .94. I really didn't change it at all. Only fluctuated from .92 to .94 with idle change.

Here's the issue, when I pulled back in the driveway, my original symptoms started again. Pulsing idle for 4-5 seconds. Once idle leveled out idle was more like 650 vs. the 850 I had earlier (car was warm at 850). Only difference was car at full operating temperature.

Took car out for another run, everything fine until I came back. Same thing happened again. I put in new IAC between test runs. No change with new IAC.

I can only conclude my symptoms occur when my car is completely at op temp (~15 min into driving). Come to think of it, my test runs over the weekend show exactly the same problem. It wasn't until I got to a specific stop light were problem would start. Car would run fine in the beginning.

My idle is perfect and car runs great initially (engine warm), but deteriorates with more driving?

I hope this isn't a valve problem...

I have a bone yard MAF if anyone thinks it would be worth it to swap out? Also have a performance MAF I haven't put on yet.

Here a list of crap i've done so far- IAC, TPS, EGR, ACT, CTS, new TB and spacer, new plenum gasket between upper and lower, set idle, tested fuel pressure, new O2s, fuel filter. Smoking system showed cracked plenum, throttle shaft air leak and EGR air leak.

I've never checked my timing. Some old timer at the local exhaust shop kept telling me to advance my timing 3 or 4 degrees to gain more horse out of a ford 5.0. I have no idea what I'm at now, but I will probably check this week.
 
So you have a vacuum gauge? That should give you a good indication if you've got valvetrain issues. This would be an ideal time to pick yourself up a gauge. They're not expensive and can be worth their weight in gold when chasing issues down.

Advancing the timing will generally help to some degree if you've got low idle vacuum symptoms because of a hot camshaft. A little ignition advance can help you pick up a couple of inches of vacuum.

Regarding the lean O2 codes....when was the last time you did a tune up? Dirty fuel filter, dirty injectors, etc could have you starving for fuel at idle. When you pull the vacuum line off the regulator, is there any raw fuel in it?
 
So you have a vacuum gauge? That should give you a good indication if you've got valvetrain issues. This would be an ideal time to pick yourself up a gauge. They're not expensive and can be worth their weight in gold when chasing issues down.

Advancing the timing will generally help to some degree if you've got low idle vacuum symptoms because of a hot camshaft. A little ignition advance can help you pick up a couple of inches of vacuum.

Regarding the lean O2 codes....when was the last time you did a tune up? Dirty fuel filter, dirty injectors, etc could have you starving for fuel at idle. When you pull the vacuum line off the regulator, is there any raw fuel in it?

I don't have a vacuum gauge, but will be picking one up.

Brand new fuel filter when I did O2s. I never did cap/rotor or plugs. The guy before me "said" he did those within 5K miles, and new wires. no raw fuel from the regular vacuum line.

Strange my problem doesn't start right away.
 
It probably starts about the time the computer switches from Open Loop where it runs on stored settings in the computer to Closed Loop where it runs on sensor input. It may still have a sensor that is marginal or has some bad wiring or bad connections.
 
So I searched a little on code 41 and 91. Supposedly there is an Orange ground wire in salt and pepper shakers that is for the O2 sensors. Several people have eluded to a poor connection of this ground wire causing the code 41/91.

Thanks, I found the bolt that holds that wire to the head extremely loose about a month ago. I tightened the bolt down snug. I didn't really clean the connection like I should have. My guess is that bolt had been loose for some time. I'll go back and do it right so I can check it off the list.