98LS1

Any recent mods? This just start happening out of the blue?

97modifiedmustangGT

we bought the car less than 2 weeks ago and it came with the problem. It's not a huge deal since noone drives it;but me and my dad would like to get it running right before we yank it and tear it apart. A race engine will be going in it.

Kick_Ass2k1

2 vacuum hoses to check in particulat: there is one that polug into the plenum on the underside front that leads to the charcoal canister.. its a long hose and usually developes a break in it somewhere (it is 20 yrs old now). Another one in particular to check is the one that goes from the inderside back of the plenum to the MAP. If either of those are leaking, your idle will surge up and down horribly. Better off pulling them both off the car, gettin in another car and goin up to napa and buying brand new hose. $5 is all it will cost for peacr of mind that those hoses are now new. even if it doesnt fix the problem. After you do that, if it still surges, get back to us.