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Discussion Starter #1
Been dealing with this issue for a while and am running out of ideas.

1997 Thunderbird 4.6L
AED SuperCharger 103k miles

When I first attempt to accelerate with the engine cold, it stumbles all over itself. It will do this for about the first 2 minutes, then the issue goes away completely. This is just normal acceleration as I pull away from the driveway and make the turn onto the first couple of streets to get out of the neighborhood on the way to work.

By the time I get to the first stop light, it accelerates perfectly fine, no issues. Operating temperature isn't fully warmed up, maybe up to 100 degrees at this point. I can watch on my scan tool to see if I can pinpoint that if it matters. Doesn't have even the slightest hint of this issue until I go to leave from work after the car has sat all day. Exact same thing, first few accelerations stumble really bad, then it clears up.

I don't believe it is a misfire issue; no backfire and no codes, and idles perfectly even when first started. Any thoughts on what to check. Mechanical issue or an issue with the tune perhaps? I have two different tunes from two different people, and it acts exactly the same with either one, so I am leaning towards a mechanical issues of some sort. I have searched out and tracked down any possible vacuum leaks.

During the past 4 months I've replaced the following:
Plugs & Wires
Fuel Filter
02 Sensors
IAC Valve
Intake Manifold Gaskets
Cleaned MAF
Harmonic Balancer

Its very consistent. Does this every time on cold start, regardless of outdoor temperature.
 

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Sound like you have a loose spark plug, or two. As your car warms up the loose plug expands in the cylinder and the problem goes away.
 

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Discussion Starter #3
Hrmmmmm... maybe. The issue did not change after changing plugs and wires; Seems it would have had an impact on that, and would impact idle?
 

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Funny thing is my car does same exact thing and I've replaced everything from tps, mafs , plugs and wires ect.
My car has to run like op said for only a min or two and then accelerates fine. But that 1st min I won't attempt to drive it as I don't wanna damage anything.
Im thinking it has something to do with the tune. My car doesn't throw any check engine codes .
If you find the issue lmk and like wise.
Im also 100% shur my plugs,wires coilpacks and vacuum is all good.
Could it be the ecu adjusting its self by chance and after the 1st min or so to fully properly adjust?
 

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Sounds like a lean condition. Obviously, your temp gauge should be reading cold and less air is used for combustion or extra fuel should be getting added. Maybe the temp gauge is reading right but the computer is getting the signal for a warm engine instead of a cold engine. I don't know what parts are involved.
 

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Discussion Starter #6
I watched what the EEC is seeing through my scan tool and the temp appears to be reading correctly. It starts at ambient temperature and rises up to 180 and holds steady. The fuel trims seem reasonable as well; I actually did some data logging and had the MAF tables corrected due to a different issue in my tune, so I would think my guy would notice if something was out of line. It did this prior to any tune adjustments and with my prior tune from a different person, but that doesn't mean it isn't the same thing.

94BadBird - are you running a stock tune, or have you had it modified? If stock, then it seems like we might have the same mechanical problem.
 

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Sounds to me like something is out of whack in open loop. Check the open loop flag to see if the issue goes away when it switches to closed loop.
 

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Could be a lack of fuel pressure at the very start? Dying fuel pump? Try priming it a few more times before you start the car, see if that does anything for the stumble.

I have a suspicion on the coil packs being an issue too, they act differently in different temperatures when they're on the way out. It's an easy thing to try, Amazon sells motorcraft coil packs for like 40 bucks each.
 

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Sounds to me like something is out of whack in open loop. Check the open loop flag to see if the issue goes away when it switches to closed loop.
This.


Try starting the car, and wait for ~130 seconds.

See if it happens.

The car still won't be warm, but there's a 'warm up timer" in the tune; IIRC, its length is settable.

IDK exactly what changes, but as Brandon said, it sounds like it clears when it goes into closed loop.

It IS a different table or set of modifiers than WOT open loop, I'm almost certain. It's more like the Choke on a carb car.

In fact, if it's using the same settings, I'd bet that would cause problems. :)
 

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Biggest change will be fueling, and possibly the spark. If the fuel tables are too rich or lean for the timing/RPM then there will be a miss. Usually though the fueling at cooler temps tends to be rich. So that's my guess - too much fuel in open loop. Data verification should immediately clarify this though.

As soon as it switches to closed loop, it runs at stoich, so unless there are issues with the O2 sensors, vacuum leaks, or other various mechanical deficiencies, fueling issues usually go away at this point.
 

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Discussion Starter #11
Sounds to me like something is out of whack in open loop. Check the open loop flag to see if the issue goes away when it switches to closed loop.
I think you may be onto something with this. I watched this on my scan tool this morning. The air temp and IAC was a bit warmer this morning, starting at 46 degrees, so the car went into closed loop almost right away. I didn't notice the stumbling nearly as bad as prior and it completely cleared up very soon, before the engine temp even hit 100 degrees.

I'll try it this weekend or next week as we are supposed to have cold temperatures again to see if I can drive it more while still in open loop to confirm the correlation. I'll report back with the results.
 

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Finally got my problem solved with the stumble on acceleration it was after changing fuel injectors mass air flow sensor IAC TPS oil change fuel filter seafoam and probably a few other things I forgot that I changed and then I finally took my jerry chip ECU piggyback out and put in my Superchips that had a custom tune and I finally had the upgrades to match the tune and it completely cleared everything up I'm thinking the engine was getting too much air at first and that the computer had to adjust and once adjusted it ran fine but that's exactly what it felt like ,like it was getting way too much air. but I would double check on the tune. Maybe it needs less timing until it's warmed up
 

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sounds like what i had i ended up changing the throttle positioning sensor on the throttle body.
i would change that and the fuel filter
the filter first then the tps.
i had to replace that in the pic it is for the spark relay or some thing like that it is for a 97 thunderbird. it seems to help it i also did a tune up and change the wires as well.
all in all check the fuel filter and the tps first let us know if you could narrow it down
 

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disregard the last post.
but what superchip did you use i am wondering to be honest because i am looking for one that i would like to use but i noticed that there are newer ones out that don't really work for our cars.
 

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I don't want to start a new thread, but my *stock* '97 is experiencing the same symptoms of late. Usually it does it when it's cold - after an overnight break,for example - but it can go from a smooth idle to a rough one just like that, say, at a stop light. It will stumble early on when cold. It's never EVER done that. The other day while I was having the oil changed, I started the engine and it ran smooth for a couple of minutes and suddenly it acted as if I pulled a spark plug wire off. The engine was warm at this point.

I know I'm due for some plug replacements, and maybe some plug wires since I've never replaced them, but could it be anything else? I've cleaned the MAF, and IAC valve, checked all the vacuum lines, and electrical connections. Whenever I've needed to unplug the battery, it usually gets back to normal within a couple of days.

It could be all a coincidence, but it started doing it a little after I had the transmission rebuilt recently. Hardly noticeable at first, but now very noticeable when it does it. I replaced the oil coolant adapter the other day, but that didn't involve unplugging anything. What connectors, etc, might the transmission mechanics have worked with, or left off, if that's the right rabbit to chase?

...One more thing. I took it to get smogged this past Wednesday and the mechanic, who I've gone to for years, came back with the following, "I've got good news and bad news. Your emissions are good, but it won't allow me to check it now. Did you recently disconnect the battery (which I had) recently" ? The print-out said, "the OBD system was not ready to test" and he told me to bring it back Friday (today) to see if it had gotten back in sync.

Anything here? Thanks again, guys.
 

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Yours sounds like a definite coil pack issue. Coil pack on its way out.
It drove pretty good yesterday, except for that initial "stumble" for the first couple of blocks.

If it were the coils, which I grant you I have never replaced, wouldn't it behave in such a way all the time, and not just when it's cold?
 

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The coil packs are a funny thing. They have a lot of symptoms. Temperature? is a major factor, mine used to only stumble when it was warmed up, some coil packs might stumble when cold. Some under load, and some at idle, it's a hard to pinpoint issue and sometimes doesn't really make sense, I guess the coils inside the coil pack crack in different fashions? I don't even know. But with these cars the general consensus for stumbling and misfiring is something wrong with the MAF or coil packs and spark plug wires, or both. Usually fuel delivery is not an issue.
 

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Well, it's been running better the past couple of days so I took it in to complete its smog test and it failed in two categories, CO (carbon monoxide) and HC (hydrocarbons) at 15mph or less. The smog technician, a German guy that operates his own smog shop and who I've been going to for years, thinks the CO is affecting the HC. Fix the CO issue and the HC issue will likely clear up, he said. It passes everything at 25 mph and over.

The thing is, it seems just about anything can affect the CO.

Anyone want to try for a homerun?
 

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Since you appear to be highly modified with a supercharger I'd expect you are a bit lean at low rpm. Could your timing be a bit off, like advancing too quickly or the base timing off?
 
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