slight miss/buck when at steady speed

[blue87lx]

im a drive at 1 steady speed my car feels like it has a slight miss or buck. what would cause this? cap rotor plugs and all got very low miles on them. not enough fuel pressure?

 

[Oldskool]

Sounds like you may be experiencing a lean surge condition, especially if you find it goes away when you ease into the throttle. Try increasing your fuel pressure slightly to richen up the fuel curve.

 

[blue87lx]

ill look into it tomorow thanks. also.. after it sits say overnight and i start it up my idle surges until it warms up

 

[Rynb15]

had a similer problem once. Ended up being burned plug wire from headers. Mine were new as well.

 

[Black1987Stang]

Check ur maf, mine does the exact same thing and many others on here...one guy on here had been tracking down the same problem and it was his maf...mine sometimes like to go weird on me too, clean it with a rag (Very Gently) and some brake cleaner and reset the computer and its all good....did u pull the codes?....i doubt the fuel pressure will do it since the computer adjusts it for you no matter what pressure its at (to an extent of course)...computer doesnt control it at WOT though....but anyways, i would pull codes, check for vacuum leaks, etc

 

[vristang]

ill look into it tomorow thanks. also.. after it sits say overnight and i start it up my idle surges until it warms up

The surging idle checklist by jrichker should help you out with that. It is very detailed and located at the top of the 5.0 forum.

jason

 

[Marlboro_Man]

I had the same problem and it was an o2 sensor. Try pulling the codes and see what you get. check the sticky "surging idle checklist" for a how-to on pulling the codes.

 

[blue87lx]

bumped up fuel pressure.. same problem. could timing be it? its at 12 degrees right now. i just dont understand this. itll burn the tires 1st and 2nd and scratch 3rd pretty easy but if i just want to do 50mph steady it runs ****ty

 

[vristang]

bumped up fuel pressure.. same problem. could timing be it? its at 12 degrees right now. i just dont understand this. itll burn the tires 1st and 2nd and scratch 3rd pretty easy but if i just want to do 50mph steady it runs ****ty

Have you pulled the computer trouble codes? This could help alot, or do nothing for you, but it is worth a try.

What fuel pressure were you at before? And now?

It sounds like a problem with closed loop running, which uses O2 input. If the O2s are out of range (old) then it would cause part throttle/cruising issues. Since O2s are ignored at wot/open loop, the problem would not affect power.

my thoughts
jason

 

[Black1987Stang]

Fuel Pressure won't affect it, basically only affects the fuel control under WOT...the computer adjusts it for normal driving...if u do turn it up or down the computer just compensates it with the injector pulsewidth...Pull ur codes and clean ur maf, i bet its the maf...try a friends known good maf to see if that is it, if u got a junkyard u could even use one from a V6 taurus...i got one on my car right now, its the exact same part number...i also used to have a v6 taurus SD computer in my stang too...dont no how a v6 computer controlled a V8 but it worked...

 

[blue87lx]

gonna check codes tomorow fuel pressure was at 32 i bumped it up to 40. found that the plate between the throttle body and iac had the screw all the way in so im gonna play with that tomorow and i also noticed if i unplug the iac or tps nothing happens and in my other stang there was a noticeable difference. any ideas?

 

[HISSIN50]

FWIW, Jrichker's wonderful Surging Sticky was removed for some reason.
A good idea is to PM mods to have it reinstated if you liked it (I thought it was a wonderful reference, as he did a great job synopsizing it to help us out).

 

[blue87lx]

i backed the timing out 2 degrees and it stopped