Bucking under no load
 

Hi
My 89 5.0 is having troubles it wants to buck under low RPM no load situations. And then other times it does fine it just does it when it wants like something is turning on and off it might do it for 10min or 5 at any time, but its really getting old and I don't even know what would cause it to do this. please help
thanks

Re: Bucking under no load
 

I just had the same thing happen to mine. There are probably a few different things that could cause this, as in most cases. In my car, for the past couple of years, I noticed that every now and then when I started my car, it would cough and struggle to stay on for the first two or three seconds after start up and then surge up to 1100-1200 RPM for one second and then immediately drop to normal idle. I would keep the plugs, wires, cap and rotor new and the MAF and idle air valve clean and this problem would still occur randomly. Then one day it started to do exactly what you described. It would buck and hesitate under low load in high gear. I popped the hood and noticed a slight hissing sound. I traced the hissing sound to a very small crack in one of my vacuum hoses. After replacing the hose, all the above problems went away and the car idles smoother than it has it two years. Sometimes these kind of problems come and go. In my case the hose must have moved slightly during engine vibrations and movements and ulitimately the crack grew more permanent. In my case it was the hose going from under the upper intake manifold to the evaporative emmisions canister. Good Luck

Re: Bucking under no load
 

I agree with the vacuum leak theory.
Had the same bucking problem and then found the vacuum leak in one of the lines under the intake.
It was a PIA to take the intake off but it was a big relief to find the culprit.
She runs great now - and best of all - NO MORE bucking!!!!!!!!

Re: Bucking under no load
 

I three had the same problem, however fixing my vacuum leaks didn't work- I had just put a 1" spacer on my intake and it started. Turns out she wasn't getting enough fuel. If you haven't added anything it would most likely be a vacuum leak or kink in a vacuum hose.
The main ones on my car that were bad were the one going to the Fuel Pressure Regulator, the one going to the charcoal canister, and my intake gasket had broken when I put the new one on. If you do hear a hissing noise, spray carb cleaner around with motor running until you hear it stop... that's your leak!

PS: Carb cleaner and paint DO NOT MIX...

Re: Bucking under no load
 

Really I have a 1" spacer on
I will try upin the Fuel Press cause I have a adjustable reg
I will also check the hoses
Thanks
Everyone