Rough Idle when Cold

Ok, 2003 Windstar Se 42,500miles. I recently performed a major tune-up,plugs/belt/fluids/filters..and so on. Well lately it runs rough before warming up. I can start it fine and it idles good for about 5mins then weather it's in gear or not it starts to run rough, kinda surging, but never dies. My wife says she saw the Battery light come on the other day when it acted up at a stop light. Once you give it a little gas it smooths out, until you let off. After it reaches temp no problems. I just checked the alternator and the battery both check out fine even under load (headlights/radio/turn signal/ heater). I will say that when I turned everything on the meter dropped to 13.8v back to 14.3v every time the turn signal flashed. Alternator outpu reads 14.6 under no load. Terminals are clean. Now correct me if I'm wrong, but I thought I would see a spike in volts under load showing the alternator was trying to compensate for the load? Any ideas thanks!:banghead:

I wouldn't expect a voltage spike as the load increases. The voltage regulator limits the upper end and it is designed to output to maintain a certain voltage range under normal load. However, when there is a sudden large load on the electrical system, there definately will be a spike up in Current. And depending on the type of initial load, the current will either spike up and settle to a high level or just step up to a high amount. But none of that solves your real problem.

Did this problem exist before or just after the tune up? Have you double checked everything tight, loose, connected, etc.? I am a little suspicious of something going on with your alt, but I don't know the correlation with it and your idle. What kind of voltage are you experiencing during the rough idle? and does it happen every time? Did the problem your wife experience happen when the van was warmed up as that would not be consistent with it being ok when warmed up? Any cel codes?

No codes. I checked everything for snuggness yesterday too. The only thing I can recall is the headlights pulsing slightly before the tune up. I was getting a Left Bank Lean code before but I corrected that when I found a loose vacuum hose on the intake and cleaned the mass air flow sensor. Like I said it does not seem to happen all the time. If it is cold out then we get the rough idle before it is fully warmed up. So I not been able to reproduce the problem when I want so I can check it (of course). When my wife had the problem it was cold out (38 degrees maybe) and she had not let it warm up. I agree with you about the voltage spike, I just found it strange that it never got above 14.7v under load and bounced back n forth when the turn signals were on from 13.8 - 14.3v. I have noticed a slight whirring sound though, kinda sounds like a supercharger (alternator??). Thanks for the response!:thumbsup:

Maybe I didn't explain myself well enough. The voltage dips WILL ocurr when a load is applied like your signaler, headlights etc. I guess you mean it makes a quick jump up or down. Since I wouldn't call a 0.5 v change a spike in voltage I was thrown off, but so far I'd call all of that normal. How is your battery? It may be worth having AA or AZ load test it for free. That could account for some of your operation problems. Not sure if this is right, check engine coolant temp (ECT) sender, IAC, IMRC. If the problem goes away at ablut the same time as you get heat inside from the vents, i'd try checking the ECT first. You should take a screwdriver or like to listen right behind your alt pulley to listen to its front bearing it sounds like. I have a Napa replacement alt that sounds like that too , that I will eventually have to replace.

Same thing happened to my Windstar, 2002 SE with 68,000 miles. Would idle rough when cold out but only after it was run for a few minutes. And yes the battery light would come on when the RPMs dropped and it was surging just like you described. It did this for months and no codes were thrown. Then I finally got the PO171/PO174 codes. Turned out to be the Insulator bolts in the lower intake were leaking air. Now that the intake gaskets and bolts have been replaced it idles perfectly.

When the air is leaked into the intake manifold the computer fights to try to get the engine to idle smoothly. This is because air is going into the engine after the Mass Air Flow meter. The computer struggles to deal with it hence the surging and rough idle. When the engine is hot the intake expands, less air is leaked, and the engine needs less fuel so its not noticed. When the engine is completely cold its on fast idle/rich start mixture mode and its not noticed then either.