ive had a 89 350/5.7 since last march and today for some reason my idle got all funky. when the car is in park, nutrual, and all forward gears (1st 2nd drive and overdrive) it revs itself at idle. instead of the usual 700rpm idle it drops to 500 then revs itself to about 1200-1400 rpm then drops to 500, starting all over agian. in other words it no longer has a smooth idle. any ideas of why this is happening? ohh and the volts go up and down with it, the lights dim then brighten back up. any help would be appreciated thanx

 

Prolly a combination of problems. Either your voltage regulator is busted or you have a bad battery with a cell that cuts in and out. I would check the MAP and the AIC sensors.

 

Not sure about the voltage going up or down, but the idling issue, sounds exactly like what my 89 firebird was doing and it was the mass air flow sensor. This may not be it if the voltage is screwing up too but maybe check it out.

 

Let the car idle, pop the hood and gently tap on the MAF.

If this can change the idle or the cars behavior in any way...time to locate a new MAF.