My car bucks and Jerks when trying to maintain a steady speed. I have repalced or looked at almost every sensor/component in my car. I have replaced Throtle body, Mass air, rotor cap, plugs, wire, MSD box, coil, Fuel regulator is accurate (set at 38psi), etc... car runs great under acceleration or idle.
Any one ever had this problem. I am sick of dealing with this problem.
65 coupe - parts cabinet, next on list! (wifes car)
69 fastback - awaiting restoration, STILL!
69 coupe - long-rod 289 done, finish fine tuning when snows gone!
82 GT - 306 long rod engine project, just starting on motor build.
84 GT -money pit street car project thats donating parts to 82 GT this spring!!!
It is a 5 speed and the timing is set at 12.5 degress. I have not changed the fuel filter yet. The car ran great, then I swaped the heads and intake, now it runs like crap. I think its gotta be electronic related. I have replaced everything from Throtle body to mass air to MSD and coil, wires rotor car plugs, etc..
when it does the bucking, do the rpms drop down significantly like from 2k to 1k then back up. If so, then i would HIGHLY recommending swaping a distributor w/ a friend or getting one from a junkyard for 25 bucks... sounds like the problem i was having that NO ONE heard of before... I did see ONE post on corral.net w/ someone who had the same problem, too bad i didnt read it until 5 months after finding out myself what the problem was.....
The computer came back clean. The wierd thing about it is that my RPM or Fuel preasure gauge do not move when the bucking occurs. It happens in 3rd, 4th, or 5the gear at any rpm when just trying to maintain a steady speed. The car runs great wide open or when idle. I have a cobra mass air conversion. Suppose to run 19lb mass air with the 24lbs injectors. Car was idleing like crap. I added a 24ln mass air and the idle and surge cleared up. Who knows? I have dropped soooo much cash into this thing in the last month, I feel like selling it. The local speed shop has tried everything that they can think of. The car ran perfectly before i swapped heads and intake. Nothing else was changed. I can not believe that the air flow with new set up could effect the computer that much, maybe it is?
I have a '88 convertible that when I purchased it it did the same thing and had a crappy idle. The car has a cobra intake system, 306 block and I think an E cam but it was speed density. I then installed a CL MAF and 24lbs injectors. The idle is now beautiful but the jerking and stuff is still there when I try to keep a steady cruising speed. It is a little annoying. I have tried everything, the car is perfect otherwise. To describe the jerking on my car, just think as if you are trying to cruise at 20mph on 5th gear or so, that is the kind of jerking my car has, if yours is like that, I do not think that there is much hope. I know I am not solving anything with my comments but I thought I let you know that yours is not the only one out there with these issues.
Originally posted by Tominator Sounds like an EGR or related sensor problem to me.
That's what I was thinking earlier.
You could try disconnecting the vacuum line from the EGR valve. I run mine without the EGR , but have the electrical harness connected. When I tried to run it with EGR , it ran very weird and felt like a backfire ? I never replaced the EGR valve because it is very expensive and it was working fine without it.
I do noy have the vaccumm line hooked up to my EGR either. Just electrical. I really think it has to do something with the computer or the electrical system (MSD wire) Car ran great before head and intake swap and I also move dthe MSD box. Ihave the Z3X 93 Cobra computer. I am trying a standard ford computer this week to see if that swap helps. I can't believe that this can not be corrected. There are plant of high horespower mustangs running around that do not buck and jerk. My entire motor is basically Edelbrock, the stuff is made to wrok together. When I figure it out, I will let you know. I have spent too much cash on this car to have it drive like it does.
My thought is that if you have no engine knock under acceleration, but the car “chugs” or “jerks” at cruising speed (light throttle application), you are getting too much vacuum advance on top of the mechanical advance.
I read somewhere if the idle is set too high that it will produce this effect at cruise.
I've been browsing a lot of forums of late and this seems to be an all too common problem on modified Ford 5.0s.
Never seen a sure fix posted.
I hate to say it, but the dealer has the equipment needed to find the fix, but not too many dealer mechanics know how to properly diagnose problems like this.
My Ranger exhibits this problem, but I'd describe it as a cutting out. Like a bad plug or wire. Maybe a clogged fuel filter. However, it idles fine and runs like a striped ass ape at WOT.
Seems to be somewhat worse during colder weather...
HELP!!! Bucking and Jerking at cruising speed 
