Rough Idle Only When In Gear

This is a little odd. Over the last two years or so the van had developed a rough idle issue. When left to idle in Park or Neutral the roughness would usually lead to the engine stalling after a few minutes.This happened both in and out of gear but only when the engine was still cold, idle returned to normal once normal op temp had been reached. Cleaning the IAC got rid of the problem... sort of. Now it idles fine in Park or Neutral but when in gear and engine/tranny still cold it is still very rough.

When waiting at a traffic light with my foot on the brakes the van shudders as it tries to lurch forward, the shaking is very noticeable even to those outside the van. This has become so bad I shift it into Neutral every time I need to stop at a traffic light, and it instantly settles into steady smooth idle at 800 rpm. However once the engine is warm everything returns to normal. Another thing I noticed is that when in gear and cold the roughness only occurs with brakes applied. Feels like whenever the roughness in the engine occurs the transmission attempts to override the brakes, which causes the lurching.

While the problem only lasts 5 to 10 minutes until op temp is reached it is nevertheless very annoying and driving me nuts. My main concern is that it may eventually cause damage to the transmission to be tugged at and jerked around in such a way. I am running out of reasonable explanations as tho what may be causing this and have begun elaborating more esoteric theories. My latest one is that since this only happens when the brakes are applied then the tiny voltage required to activate the brake lights is somehow causing some other electric part to fail, and that the rough idle is somewhat related to this. Shows you just how desperate I'm getting.

Anyone here ever encountered this?

I'm also wondering if the tranny is fully easing up.
It should still provide some engagement...but it would have enough slip in the torque converter to avoid bogging down the engine.

I guess the FIRST thing I would address is any routine maintenance items....including transmission fluid (use a fluid that meets the Mercon V specification).

Vaccum leaks are another thing that I would look into.....as in condition of all the vaccum lines...including the PCV hose.

One point mentioned by Wiswind is a vacuum leak and according to your post, condition seem to be worst when you apply the brake which use (if I could say) a big amount of vac to operate the booster. If not already done I would take a serious look at the few vac hoses between the engine and the firewall, in addition to the brake booster, there is another big one connected to the base of the intake plenum on the passenger side and also a few little which feed the Vapor Canister Purge Valve and the EGR Vacuum Solenoid (on the firewall). Just a few idea if not already done.

A-ha! Now we're getting somewhere. Thank you gentlemen, off to check vacuum lines. This killer heat will make things even more interesting. Forecast heat index for today was supposed to be around 90F but at 10 am was almost 100F already :newburn:

Ditto on vacuum system. And there may be a leak in the brake booster itself.

That hot in Montreal?

That hot in Montreal?

Sure is, Montreal is noted for its perfect incarnation of the Humid Continental climate zone the main feature of which being temperature extremes exacerbated by consistently high humidity levels. I have lived some years in Phoenix and I can tell you 100 degrees there feels quite cooler than 80 degrees here and it's way above 80 now. If one wants to experience what it feels like to live in Africa and then what it's like to live in Antarctica, Montreal offers both every single year. In summertime it is often hotter than Miami here, and no soothing sea breeze to cool you down in the evening, often no wind at all at night. In winter it is sometimes colder than Moscow and always, always that dang humidity. I have no idea how people managed to survive here before the advent of AC and central heating.

Needless to say it's kinda rough on vehicles :(

So when it became obvious that I couldn't perform a vacuum check without removing the cowl I opted to postpone the procedure until this evening and do my coolant flush this pm instead. Got two gallons of demineralized water and a quart of concentrated coolant at the ready, that's my van's summertime cocktail. Beamer only gets water with a dash of rust-proofing compound. I only drive it in summer and it has never tasted antifreeze according to previous owner, I purchased this car in Arizona (Tucson) where it had spent its whole and rather sedate life. I bought it on a whim because I had never seen such a small V8 before, it's only 4.0L. It is sluggish and Winnie beats it on acceleration lol

Cool front is working its way toward you......it moved into Wisconsin a little later than expected....but it feels MUCH better now than it did earlier.

If you have a 1999 or newer windstar, do not forget the isolator bolt TSB........folks have posted that this vaccum leak can be worse when cold.

Cool front is working its way toward you......it moved into Wisconsin a little later than expected....but it feels MUCH better now than it did earlier.

If you have a 1999 or newer windstar, do not forget the isolator bolt TSB........folks have posted that this vaccum leak can be worse when cold.

Cool front will be greeted with open arms and open windows yay!!!

Isolator bolt check added to to-do list, thank you :)

I believe I have finally narrowed down the list of vacuum leak suspects to one: the brake booster itself. I have noticed that if I turn the engine off while stepping on the brake the pedal immediately becomes stiff as rock. This is not supposed to happen, normally the brake booster should hold enough air for a few assisted applications even after the engine is shut off. My theory is as follows: if the booster's diaphragm is ruptured but the booster casing is intact, power brakes will still operate but only as long as there is "live" vacuum (i.e. engine is running). Loss of diaphragm should normally prevent the booster from keeping any "reserve vacuum" once the engine is turned off.

As I was expecting a new brake booster costs a small fortune, so I guess a trip to the junk yard is in order.

Instead of purchasing a brake booster at the moment, I think you should be able to remove the vacuum hose from the booster, plug it, and let it run. The hose does not need to be connected to the brake booster to run the engine. If the engine runs well, problem found. If not, back to the grind stone.

Instead of purchasing a brake booster at the moment, I think you should be able to remove the vacuum hose from the booster, plug it, and let it run. The hose does not need to be connected to the brake booster to run the engine. If the engine runs well, problem found. If not, back to the grind stone.

I purchased two boosters :biggrin:

But those are junk yard units at $8 apiece, and I will do as you say prior to installing anything :)

If none of this proves to be the issue, I'd check the motor mounts next. Broken or worn motor mounts often exhibit symptoms that can be difficult to pinpoint.

If none of this proves to be the issue, I'd check the motor mounts next. Broken or worn motor mounts often exhibit symptoms that can be difficult to pinpoint.

Interesting. It just so happens that the motor and tranny mounts are due for replacement, one is obviously on life support. I keep postponing this job because it involves using an engine cradle and special jacks. Also the mount and subframe bolts were unremovable even with a 42-inch breaker bar but I purchased an IR air impact wrench and it appears to have no trouble at all spinning off those rust-welded nuts, judging from a few trial runs. Still, it's a day-long job I would guess.

With regards to the brake booster I did as suggested and it didn't change anything, even with the booster off the vacuum stepping on the brakes still causes rough idle that returns to normal as soon as I let go of the pedal. This only happens when tranny is in gear, stepping on the brakes when idling in Park or Neutral has no effect, idle remains normal. It would seem that a vacuum leak can be ruled out as the cause.

When the tranny is engaged, the engine twists a bit under load ... not so in N or P. What air leak would be more apparent if the engine twists?

Under load, the idle is slower ... could it be the IAC is at fault?

When the tranny is engaged, the engine twists a bit under load ... not so in N or P. What air leak would be more apparent if the engine twists?

Under load, the idle is slower ... could it be the IAC is at fault?

Been wondering about the IAC myself. I used to have a rough idle issue only when on N or P so I cleaned the IAC and that fixed the issue. But now that I think about it, this was around the same time the rough idle in D issue appeared. I suppose it's possible I inadvertently performed a "politician fix", solving one problem by creating a new one that's worse :banghead:

IAC issues go hand in hand with throttle body issues ... make sure the throttle body and plate are clean and everything around lubricated ... WD40 or the like.

Greetings to All!

This is my very first post in this forum. I have heard many good things about this particular forum and the folks that inhabit it!

I have a 2002 Windstar SE that has this identical issue of idling rough while in gear, but not in Park or Neutral. Now she keeps throwing a TC that indicates a wee air leak in the intake manifold. As I am on a pension, I have demurred on that repair until it becomes an absolute necessity. I have had two professional mechanics check her out for vacuum leaks as have I, but none of us could identify one! (which came as a bit of a surprise, really). Cleaning the idle air control valve is a new idea for me, so I will plan on doing that today or Tuesday, depending on how busy I am today. Is there anything else in the realm of regular maintenance that I want to pay special attention to? Yes, the air filter has been replaced in the last month! LOL

Can you post the P-codes you get from the scanner? The specific codes are vital to helping track down the problem.

Thank you for your reply scubacat. Unfortunately, I cannot provide any P codes related to this issue at present. I am unable to find my notes that lists the singular code that was thrown. I have a friend who is a master mechanic coming over this weekend to help me with my van and I'm certain he will have his diagnostic computer with him.

However, I did forget to mention one possibly significant fact that makes the issue I am having different from the issue described by the original poster and that is the rough idling issue is present whether the engine is cold or at normal operating temperature.

I will update this thread with the P code and the results of cleaning the Idle Air Control Valve as soon as I possibly can.

Ok. If it is, in fact, a lean code, check the P0171/P0174 sticky thread. That's a well known issue with the lower plenum bolt grommets and a fairly easy and very cheap fix. If there's a misfire, check that, the EGR ports, and the coil pack for cracks. Those are the 3 usual suspects.

It would be helpful if you'd post the type of engine (3.0 or 3.8 L) as well as the mileage on the engine.

There are a number of root causes for rough idle while in gear. Some are relatively simple, others take a little more teardown & repair.

First, lean operation due to a vacuum leak doesn't necessarily mean misfire (rough). The computer can compensate for significant excessive air entering the intake without leading to misfire.

It is helpful to check for oil in the throttle body and plenum (boot between the throttle body and the air filter). This oil is a sure sign of blow-by (due to worn rings). The extra oil might be enough to give a lean reading due to unmetered "fuel" entering the engine (since the oil burns). Similarly lean codes can be the result of a malfunctioning fuel injector if it releases too much fuel.

I've had misfire issues that were related to the EGR system as well. When the EGR are ports are clogged you can get misfire under light acceleration. An EGR that sticks open might cause issues at idle.

Another source of misfire can be the Idle Air Control Motor located on the intake near the throttle body. If the IACM is malfunctioning then the computer can't optimally adjust the intake air flow at idle.

Thanks some more scubacat and thanks for weighing in tomj. She has the 3.8L engine with approximately 141K miles on her. In thinking about the specific trouble code thrown, although I still am unable to find my notes, I would swear an oath that I was told it was due to running lean. Therefore, I will be checking out the sticky topic that you recommended scubacat. While she does idle roughly, I don't believe there's a misfire involved. I have experienced misfires in a previous Windstar that I owned and they are significantly more violent than what I would describe as a significant vibration that I am experiencing presently with this Windstar. Also Tom, when I replaced the air filter for her earlier this summer, I did closely inspect the insides of all the different components that I had to disassemble to get the filter out and back in again. Despite her high mileage, I am pleased to be able to report that I found no sign of oil, either visually or by feel anywhere along the exposed air intake pathway. I will be checking out the EGR valve the next chance I get.

I did get around to cleaning the idle air control valve yesterday. There was some soot present inside the valve and it was cleaned out as thoroughly as I possibly could. The spring is intact and the valve inside the housing moves quite freely. However, I did not notice any appreciable change in engine performance when I drove her last evening. It was only a short distance, so perhaps I'll notice some difference while out and about today.

Thanks again for all of your excellent suggestions! I'll continue to update the information as I uncover it.

Is the check engine light (MIL) on? Don't overlook AutoZone's free code reading service.

It is good to know that you don't have oil in the intake, even at 141k.

My experience with the EGR issue is that the system can be clogged.

My first experience with clogging was at the EGR "ports" which are located in the lower intake manifold. There is one for each cylinder. They are accessible by removing the upper intake manifold (plastic piece) and can be cleaned with a combination of solvent and mechanical removal (I've used a drill bit and a wire brush). I use a vacuum to suck and removed material from work area before it can fall into the intake. It's a fairly common operation that is frequently discussed on this forum.

The second EGR clogging experience was in the EGR pipe between the exhaust manifold and the EGR valve. The EGR pipe has two small tubes that are located on ether side of an internal orifice. The tubes and orifice allow the DPFE to sense the amount of exhaust gas that is flowing back to the intake. I was able to remove Soot clogging the small tubes with a small piece of music wire and heat (applied to the tubes) to "cook" it. It think I tried solvents as well, but the heat was required to burn out the clog. This clog was indicated by a stored trouble code indicating a malfunctioning DPFE.

Don't overlook the ignition system. Make sure all the plugs and wires are in good condition. Some old fashioned vacuum gage analysis might be of help as well.

Thanks for the follow-on about the EGR, tomj.

I happened to Stop at my neighborhood O'Riley's Auto Parts today and had them check the P codes. Sure enough, the codes came back as P171 and P174! So now at least my course is clear. It'll have to wait until at least next month as money is extremely limited for the rest of October and there are any number of PM's I intend to perform while I have the Windstar's cowling removed, not the least of which is replacing the wiring harness and plugs, cleaning/replacing the EGR and dealing with that other component that seems to like to take a dump once the P171/174 issue is resolved. Just hope the weather stays fair until the work is completed!

Hey Guys! Been studying the sticky 'bout fixing the problem for the P codes 171 & 174. REALLY like the link to the webpage (http://leckemby.net/windstar/windstar01.html) and the fact that he covers the P code 0401 as well since it seems to regularly follow fixing P171&174. I do have a couple of questions that I'm hoping you can help me with. First: Rather than replacing the valve cover on my engine if it indeed has the notorious hole in it, could I just clean it up thoroughly and patch the hole with some J.B.Weld or the like? Second: Could someone please tell me what the acronym DPEE stands for? I just cannot figure it out! Thanks all!

Not sure on the valve cover. It's a design issue; the hole is just how you identify it. I'd replace it. I believe you can get an after-market part for not too much (or a junkyard part from a newer model that has the updated cover).

DPFE = Delta or Differential - Pressure - Feedback - of EGR. It's just a fancier term for "EGR Sensor". Surely somebody concocted it in a Ford corporate-level meeting to score brownie points.

Anyway, the DPFE sensor is what fails and can trigger an EGR code. Clean the ports in the manifold when you have the cover off and replace that sensor, but do NOT waste money on an EGR valve. They almost never fail. The code(s) can be misleading and tempt you to replace that valve, but you'd likely be throwing money away doing so. The DPFE sensor is usually around $20 and takes one minute to replace.

You also do not have to replace the plenum bolts, so no need to fork over the ransom for those from a dealer. You can just cut off the grommets and get another set for about $8 from rock auto; the silicon upper plenum gaskets ("port seals") are just a few bucks as well; replace them too. Even if you already have the green grommets, that is where your vacuum leak is occurring, so just replace them again. The green ones are improved, but nothing is foolproof. And, they're cheap anyway.

Two other things to check when you have the plenum off: First, the little white "IMRC" bushings. They'll be on the little metal actuator arms on the left side as you're facing the engine compartment. It's $5 for a 5 pack from an auto parts store (a dorman part). Once again, don't get gouged by the dealer for those. Even if they LOOK ok, they may be on the brink of disintegration like mine were. Do yourself a favor and replace them when you have easy access. Second, the water bypass tube you'll see attached with 2 bolts across the metal intake manifold. It will eventually leak at the 90-degree bend. It's about $32 for a new one from rock auto and $70 from a dealer. I replaced mine (for $32) preventatively. You can skip this, but you may be removing everything again someday if that springs a leak. Just something to keep in mind.

Good luck!

Flat out AWESOME info, scubacat! You can count on me using every bit of it too! Thanks SO much!

Not sure on the valve cover. It's a design issue; the hole is just how you identify it. I'd replace it. I believe you can get an after-market part for not too much (or a junkyard part from a newer model that has the updated cover).

The best price I found for a new, after market LH valve cover was 50.00. On the other hand, while I was pricing parts for this repair, I found several places that offered ALL of the needed parts together in sort of a 'kit' form AND at a substantial discount! The one I'm going with was found on E-Bay and has the kit priced at 96.90, delivery included versus 172.27 buying each part individually from a variety of suppliers, some online, some brick and mortar stores.

DPFE = Delta or Differential - Pressure - Feedback - of EGR. It's just a fancier term for "EGR Sensor". Surely somebody concocted it in a Ford corporate-level meeting to score brownie points.

Isn't that just typical? Ask an engineer what time it is and he tells you how to build a freakin' watch! LOL

Anyway, the DPFE sensor is what fails and can trigger an EGR code. Clean the ports in the manifold when you have the cover off and replace that sensor, but do NOT waste money on an EGR valve. They almost never fail. The code(s) can be misleading and tempt you to replace that valve, but you'd likely be throwing money away doing so. The DPFE sensor is usually around $20 and takes one minute to replace.

Yep. Found one online through my pal E-Bay for 23.00 including delivery.

You also do not have to replace the plenum bolts, so no need to fork over the ransom for those from a dealer. You can just cut off the grommets and get another set for about $8 from rock auto; the silicon upper plenum gaskets ("port seals") are just a few bucks as well; replace them too. Even if you already have the green grommets, that is where your vacuum leak is occurring, so just replace them again. The green ones are improved, but nothing is foolproof. And, they're cheap anyway.

Good information to know! Why don't you add this very relevant and money saving bit of news to the sticky thread on the P 171/174 codes issue? As for me, since you feel I should probably replace the valve cover rather then filling the hole with J.B.Weld, I think I'm gonna stick with buying the 'kit' for 96 bucks and change.

Two other things to check when you have the plenum off: First, the little white "IMRC" bushings. They'll be on the little metal actuator arms on the left side as you're facing the engine compartment. It's $5 for a 5 pack from an auto parts store (a dorman part). Once again, don't get gouged by the dealer for those. Even if they LOOK ok, they may be on the brink of disintegration like mine were. Do yourself a favor and replace them when you have easy access. Second, the water bypass tube you'll see attached with 2 bolts across the metal intake manifold. It will eventually leak at the 90-degree bend. It's about $32 for a new one from rock auto and $70 from a dealer. I replaced mine (for $32) preventatively. You can skip this, but you may be removing everything again someday if that springs a leak. Just something to keep in mind.

Yeppirs! In for a penny, in for a pound as I say! As long as I have the engine that far disassembled, I'd rather perform PM than repairs anyday! I'll scrape up the extra bucks from somewhere.

Good luck!

Thanks mate! Believe me, I'll need it (as well as a garage out of the wind and weather to work on her)!