whats up fellas? hey i just bought a 91 5.0 well, id say it had a 4cyl to start but itnow has a 5.0 fuel injected, mass air, stock t/b and mass air meter, new iac motor, it has a cam the guy told me it has a e-cam but i built the 87 5.0 i had and used a b-cam and this car i have now thumps harder than a b-cam, but anyways maybe someone can help me here, this car has a very nasty idle surge, i tryed a gasket off ebay that has smaller holes than the o.e.m gasket, i set the t.p.s @ .99. i have tryed all that i know that fixed my last mustang from the surge butthis one is being a pain in the a_s.... if anyone has any idea what it may be or know of anything i can try or buy or fix to make it stop or even get a little better than it is.. and also when driving and coming to a stop it will stay at about 2500 rpm for a few seconds before it starts to fall off to a idle. thanks for any input.
randy

 

hmmm, does the car want to die when you cold start it?

 

yes it dose, its a bitch to start ,like a carb car thats cold natured..

 

well i have the same problem. its probably the iac valve, its on the side of the throttle body. You might need to clean it or get it replaced

 

nope, its new !!!!!!!!!! try again

 

Did you do a base idle reset? Vacuum leaks??

 

well another problem would be the throttle body plate. its a part inside the throttle that flips open when you press on the accelerator and the amount it opens depends on how much you press the accelerator.
Well just like the IAC when the throttle body gets gunked up with carbon it can stop it from closing all of the way causing idle problems.

 

+1 on the throttle plate.it may be just set wrong.if it closes to far the engine opens it up then lets it fall back again hence surging. just try to turn in the little screw to hold your plate open. on mine it took only two turns in and car runs/idles perfect. you may still have an ecam.if your timing is off it can sound pretty lopey.

 

run a koer test and check for codes first.

 

I don't understand why no one does this. It only makes since to check codes because it might tell you what your problem is. Removes a whole lot of guess work.