O.k. I had problem like this drove me nuts for months finally sent it to a shop took them two weeks to find it and it pissed me off when I found what it was. Somehow the positive battery cable got wedged between the engine block and exhaust manifold it melted the insulation around it the fused the wires together hard to find the spot was 1/4 the size of a dime. The dealer had just had it in for a recall and a week later this happened dealer could not find the issue told me "its an old car with a lot of miles it does weird things when it gets old cars are like that." Took it to an independent shop and like said two weeks later he found it. I threw $1,000 worth of parts in it at dealers suggestions including a $300.00 fuel pump, MAF, pcv valve, idle valve, throttle body. Dealer wound up reapinting my hood and bumper as a deal for my not taking him to court. So anyway try replacing or at least inspection the positive battery cable.
