Bad Stumble... WTF ???

StangLou · Apr 26, 2004

Ok guys, heres the deal. Car has been running great since the L/T clutch install. This am I go out and it starts up great. I pull out of the driveway and go down to a stop sign. It starts stumbling and revs drop to around 500. I put in the clutch, floor it, and it smooths out. I hit 2nd and feel it start to stumble again. Im like what the heck, floor it in 2nd and it will barely get out of its own way. Im almost slowing down and its floored. I put the clutch back in, floor it, and it levels out again. Get to another stop sign and it starts idling fine, then it drops to 400. From there the car has a very noticable shake to it and the revs are going from 400-700. I pull out in first, nail it, hesitates some, nail 2nd pulls fine, nail 3rd and it stumbles a bit but pulls after that. I hit the next light and its idling fine. I run through the gears hard for the next few lights and getting onto the hw and its fine. Get here to work and it idles perfect. Im guessing my IAC is going bad AGAIN!!! If this is the clupret it will be my 4th new IAC Ill have to get for this car. You guys have any suggestions as to why I would be going through these things so fast or what could be wrong???

D.K · Apr 26, 2004

It may be due to the LTs. Since the O2 sensors are now further downstream, it takes longer for them to heat up, which can cause drivability problems when the engine is cold. If the problem seems to go away once the engine warms up, that would be my guess as to what it is, and it can be resolved with a tune.

downsouthman1 · Apr 26, 2004

D.K said:
It may be due to the LTs. Since the O2 sensors are now further downstream, it takes longer for them to heat up, which can cause drivability problems when the engine is cold. If the problem seems to go away once the engine warms up, that would be my guess as to what it is, and it can be resolved with a tune.

This is precisely what my car does until it warms some. I just drive it really easy for the first 3 minutes or so & it's fine.

StangLou · Apr 26, 2004

Well that sucks! I called my shop and they think it could be the tps going south on it. He said that since I hit the throttle and 2nd and it would hardly budge, hes leaning towards that. He thinks if it was IAC it would only happen at idle and I would have a hard time starting the car. The car looked fine with a/f and all on the dyno 2 weeks ago, could this problem just arise or would it have been obvious on the dyno then? Oh well, I have to take my g/f's in tomorrow to have Flows put in lol. Ill just have to tell her to put in the clutch and floor it if mine acts up on her tomorrow lol.
Ahhh the joys of Modding our cars

'96&'01Stang · Apr 26, 2004

Are you getting a CEL? Have them check your front 02's even if you are not

D.K · Apr 26, 2004

It took a week after my LT install before my car started acting like that.

StangLou · Apr 26, 2004

No, Im not getting any SES light or anything. He said it will take a long time of this happening for the SES to come on for the tps going bad. It will take so long that most people get it fixed before it does come on. Anyone know how much these things cost?

DK, did you get your tuned to get rid of it? I have a tune on my chip already. The L/Ts leaned me out some, but not enough to cause detonation so I kept the same tune that was on the chip from a few months ago. Like I said all seemed ok on the dyno pull I did. Would it have shown up there?

D.K · Apr 26, 2004

StangLou said:
DK, did you get your tuned to get rid of it? I have a tune on my chip already. The L/Ts leaned me out some, but not enough to cause detonation so I kept the same tune that was on the chip from a few months ago. Like I said all seemed ok on the dyno pull I did. Would it have shown up there?

Yes, my tuner was able to fix the issue on my car. Once he hooked my car up to the computer, he spotted the problem before making a run. It won't show on a dyno graph, but it should have shown up in your LT fuel trim and O2 voltage readings if they were being read during your dyno session.

StangLou · Apr 26, 2004

I know a/f was measured with the pulls, but nothing seemed strange then As I said before, it got me a little leaner, but there was no detonation so we left the tune alone. Im hoping it is just a tps going bad. Did yours also have hesitation like I described in mine or just a rough idle?

Thanks guys.

D.K · Apr 26, 2004

StangLou said:
I know a/f was measured with the pulls, but nothing seemed strange then As I said before, it got me a little leaner, but there was no detonation so we left the tune alone. Im hoping it is just a tps going bad. Did yours also have hesitation like I described in mine or just a rough idle?

Thanks guys.

I didn't have any idle issues. On the first start of the day everything would be fine until until I would slow to hit the second speed hump in my neighborhood (.1 mile). After that, when I would go to accelerate, it would stumble/sputter/buck and not begin to pick up any speed. If I pushed the clutch in, the RPM would drop like a rock, so I'd have to generously blip the throttle and drop a gear before the RPM dropped again. I'd have to do that at the remaining 5 speed humps in my neighborhood. Once I got on the road, and the engine got to normal operating temp, everything was fine. After the tune, all those drivability issues were gone.

00VERT GT · Apr 26, 2004

StangLou said:
I know a/f was measured with the pulls, but nothing seemed strange then As I said before, it got me a little leaner, but there was no detonation so we left the tune alone. Im hoping it is just a tps going bad. Did yours also have hesitation like I described in mine or just a rough idle?

Thanks guys.

I have an automatic and i have the same problem. And yeah mine is only bad when the car is cold. I created a huge thread about it some months ago and it turned out a bunch of us have this problem. I'm getting used to my "rpm bounce" but yeah it does suck. the other day i had it floorded in second and the car was just sitting there. If you find a fix please post it. oh and i've changed my IAC 3 times as well.

StangLou · Apr 26, 2004

I had a bad cold start problem... is this the other thread you are referring to? On a cold start it would just act like it wouldnt turn over and then it finally would. For the first little bit it would have a really rough idle? I had that issue for months. My chip actually fixed it. There is something in the tune from Ford that just wouldnt let it fire up right when cold. Now the car starts great when cold.
The problem I have now is when I first drive it, when I stop the revs drop badly and I have to put in the clutch and floor it. This is much different than the cold start problem that a ton of us had. I know you said that you had it floored in 2nd the other day and you were just sitting there, thats a lot of what happened to me today. Have you changed your tps? The IAC excuse is getting old. There are only so many times one should go bad on a pretty much new car lol. Im hoping to know more Wed after I take my car up to the shop to have them look at it.

lwkauble · Apr 26, 2004

The TPS could very well be a likely source of the problem. Before paying to get it checked, you should check and see if any disconnected vacuum lines. Also check to see if the tube leading to the IAC from the Air inlet tube is connected properly. 2wice I have had the same simptom, and 2wice it has been becasue something has come off. If the IAC tube is loose or open at the air inlet tube (after the MAF) the computer will go crazy and won't be able to control a/f ratio. Almost like a bad misfire under load. You have to fight to keep it alive. Anyway check and makesure you maifold Vac line is in place and check the IAC tube. The TPS is a common culprit on a high milage car but not for a car that is as new as ours are. Make sure your injectors are plugged in and all that. then if you can't find it, take it in. Good luck

StangLou · Apr 26, 2004

Where in the heck is the throttle adjustment screw on our cars

. I was going to mess with it some to see if I could raise the idle a bit. Why cant these things be as easy to mess with as the 5.0's lol.

JonJon · Apr 26, 2004

my car does that once in a while when it was really cold... it would stumble like crazy when I gave it more than 1/2 throttle... made me really worried my friend though i had water getting into my intake or something but we checked a few times, the engine bay was totally drive

but when a few minutes later when it warmed up, it ran good

JonJon · Apr 26, 2004

StangLou said:
Where in the heck is the throttle adjustment screw on our cars . I was going to mess with it some to see if I could raise the idle a bit. Why cant these things be as easy to mess with as the 5.0's lol.

on my accufab 75mm tb, it's on the side facing down. it's a threaded bolt with a screw on the end. turning it one way keeps the butterfly open more, turning it the other way closes it more

00VERT GT · Apr 27, 2004

stanglou, i was referring to the "rpm drop" thread i made. but yeah exact same problems. Rpm's dropping while in motion. Mine does it when i'm stopped as well though. lucky me.

StangLou · Apr 27, 2004

JonJon... on my tb, it looks very similar, but that mid right screw is just one of the 4 that bolts the tb in place.
The screw on the bottom left I dont have . its just a flat covering on mine.
The piece right in the middle of your red box... it looks like I should be able to adjust a piece that moves the throttle adjust... but again mine is weird. It looks like there is a piece of screw, but no head on it Its just a threaded peice that the little 90 degree bend sits on.
Anyone else know what screw adjusts the throttle on a stock tb 03 GT???

Oh yeah... the freaking car did perfectly fine this am . I mean Im happy, but its frustrating when there is something tedious like this wrong.

JonJon · Apr 27, 2004

dammit... that's the thing, I don't know if the stock tb even has an idle adjust screw...
Mine is in MD so I can't look at it
sorry

stang09er · Apr 28, 2004

Whenever I adjust that screw (same problem as the rest of y'all) nothing happens..,I can turn it while idling and nothing happens???

Bad Stumble... WTF ???

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