Hesitation on cold acceleration

[Strike12]

Ive helped a few and i i hope a few could help me . Gotta 91 4.0 The x has a flat spot when accelerating from stop . Idles great , starts great . good gas mileage . only when its cold . A mile or so , its fine. Just a big flat spot like a bad accelerator pump on a old carburater . Any Ideas?

 

[MyExpWork]

Mine does this too. When its cold and from a stop I will hit the gas and it hesitates for just a bit. Even when idleing in the driveway I can get it to do it.

I've got a 169,000 miles on it and when its warm or after a few minutes of warming up it doesn't do it and it only does it in the morning when its at its coldest.

I think maybe if you clean the MAF or the TB it might go away.

But since all I have to do is let it warm for a minute longer I haven't done anything about it yet.

Brian

 

[Bottomlesspit]

Just to let you know, mine does it too. The engine is pretty slugish until it warms up a bit. During the cold start, and warm up mode, the computer is adding extra fuel and time to let the engine run efficiently. It is on the rich side and might tend to bogg down slightly until it warms up. Once warmed up the computer starts taking info from the O2 sensors and trims the fuel back accordingly, leaning it out slightly. I am guessing, compared to my old mustang data, that the engines are running slightly rich.
Another old culprit of hesitation and poor throttle response is the throttle position sensor (TPS) having a flat spot in it, but I don't think that's our situation since the problem goes away when warmed up. This is just all info I have encountered in the past when tuning the stang beast for the track.
Ken

 

[Strike12]

I checked the tps , changed the coolant sensor , cleaned the maf , and cleaned throttle body , I also have used injector cleaner on a regular basis , but still no luck . It only does it for 1-3 min on a fresh cold start , and didnt do it when the weather was warm , any ideas? Thanks

 

[Strike12]

I just had a thought about what might be wrong .Im thinking a vacuum leak around the manifold or throttle body , it being aluminum might be expanding when warm and sealing the leak , maybe why it doesnt it in cold weather and not in warm weather . Ill try to retorque and check with starting fluid . Ill keep you guys posted.

 

[Strike12]

Well I tried retorqing throttle body , and upper intake and then checked with starting fluid and still had the problem . I also pulled the plugs for s**ts and giggles but they looked great and the gaps were perfect , also checked the plug wires and ohmed them out and all checked out good , recleaned maf sensor , and checked all vacuum lines with a vacuum pump , everything checks out . No CEL . Could it be sticky injector/s or even regulator , would a test on that be a good idea?Need some help , this is driving me koo koo.

 

[Mike]

maybe its just to cold?

 

[Strike12]

Well yea its cold here in Michigan , but I 'm sure thats not the problem . I know I dont like the cold much and dont feel like moving until I get my coffee , but what does this x want , I cant give it coffee , itll have a stroke. LOL

 

[Blue Steel]

gotta let your engine warm up a bit before you go in the morning. lived in canada for 14 years. it's not good for your spark plugs. if you do it often enough, the spark plugs get too hot too fast and they will mess up.