holeshot

I've had this problem for a couple years and I have just lived with it, but its starting to bother me. I dont know if it started after I put on my CAI or o/r h-pipe (cant remember that far back) or if it was there since I bought the car.
Anyway, the issue is if I start up the car (no matter what the outside temp is) and take off right away my car will drive like normal, then all of the sudden it kinda stumbles and hesistates. If I keep my foot on the gas it will start bucking around like a wild mustang...no pun intended. Now if I let the car idle for about 30 seconds or so before I take off its fine...no problems.
Anyone have this issue and if so, wtf do I need to do to fix it? Thanks!

theedge67

Never had that problem. I know mine is touchy when cold, but not so bad that it bucks around on me.

05BlackGT

Mine bucked pretty bad until I installed CMDP's and cleaned my throttle body. It was pretty gummed up, but I did install a new tune also, so I can't be sure it was just the dirty TB.

Got Oatz

+1. Clean your throttle body. Made a world of difference for me on take off....And I only have about 15K on the dial......


Mike

Rebel73

On one or two instances, my car actually stalled on me when I tried to take off immediately after starting it up. I realized that I didn't give the motor a chance to "normalize" to idle rpm's. Now I usually wait til the tach needle falls below 1000 before taking off. Been ok since.

RRRoamer

I've never had anything that bad before. I have had some issues when I'm trying to go slow in first when the car is cold. It will buck until I let off the gas. The problem is definitely the TB is over compensating (underdamped in PID controller terms) when it is cold. It could very easily be that the TB is sticking slight, causing the motor to have to push harder to get it to move, then it jumps. Which causes the TB to open TOO much so the motor tries to close it and it sticks again causing that nice little surge loop.

I should probably go get some TB clean and give it a try. It sounds like you should too!

max2000jp

My car bucks everyonce in a while if I just start it and leave. If I let it warm for a minute, it works fine. Sounds like the same issue.

I bet it's grime on the MAF. I need to clean it and my TB. Should clear everything up. These cars seem to have a decent amount of blow-by.

GottaHaveIt

mine used to alot then I put in a K&N and 99% went away then I used a SCT flash tune and nothing, and when the engine is warmed up is that much sweeter like a lady with a few glass's of wine. smooth & fast the CAR.

holeshot

Well, I decided to clean the mass air flow sensor and the throttle body. So I went out and bought a can of MAF cleaner and a can of throttle body cleaner from CRC. Took the MAF sensor out of my C&L and it looked very clean and no dirt or deposits on the wires, but I sprayed it down anyway for good measure. Then I took off the throttle body and I could not believe how dirty it was! It was very gummed up with dirt and grime. I sprayed both sides (front and back) with the throttle body cleaner and broke up most of the gunk. I opened up the valves wiped the rest out and cleaned it all up like new.
Anyway, long story short.....it still does it. Same as before...during a cold start and taking off right away. However, I highly recommend that you guys take a half hour to do this and clean these two things. I could definitely tell a difference in performance.

RedFire4.6

I have the same bucking when its cold out and i first take off i was gonna ask the dealer about it but after my fuel pump TSB fiasco i decided to just try and live with it rather than dealing with the stealership again.

dustindu4

It's normal, mine does that too.

It depends on how your tune is set up too. There is an SCT tuning parameter called "startup RPM adders" or something. It changes the car's idle for a set time after it starts. You start your car is jumps up to 1800 and slowly goes back down to 850 or whatever the idle is set at.

Because I have an offroad H and SLPs, my neighbors bang their heads on their bedposts every morning so I had Doug change my tune to remove this feature. After it starts it goes right to idle so the car isn't so loud at 6am anymore. The downside is I have to let the car idle for a minute before driving off or it will start bucking because it's not warmed up enough yet.

It has nothing to do with a dirty MAF

NJ3

Mine does the same thing but only when I use my Brenspeed 93 octane tune.

theedge67

I have heard 2 theories on the reason the 4.6's rev up high at startup. All of them do it, Crown Vic's, trucks, mustangs...every one of them, every different iteration of the 4.6 that I know of.

#1. It is to warm the cats quicker for lower emissions.
#2. It is to help with the timing chain tensioners. They work on oil pressure, and a quick rev up gets the oil there sooner, reducing timing chain rattle (which owners hate) Our CV's at work all do it because of cruddy oil filters with no anti-drainback valves. It sounds like the engine is going to knock itself to death for about 1-2 seconds until oil pressure builds up. So far though, no problems with them with over 5 years and 90K miles on several of them.

That being said, I personally think it is due to the timing chains. With a good oil filter, such as a Motorcraft, it should not be an issue, as the pressure will build almost instantly after startup.