Very low idle and dimming lights, Celica had a heart attack ?? Options

[Remy]

Hey all, this morning I was driving to work on the highway and as I was approaching my exit this truck started tailgating me I was like wtf ? So I switched lane and he followed me as I got close to my exit he was still right behind me so I down shifted and took the exit and lost him as I approached the stop lights and coming to a stop my car started idling down to 150-200 and my lights and interior starts to dim down really low I though the car was gonna die on me, it was a good thing my work place was just down the block.

So I got to work and turned the car off and went inside, after I got off of work I started the car and it ran just fine drove it home (took the small street though). At first I though the alternator died on me or was going out but I drove it home after work just fine no problems at all and good idle too...? My other though was maybe its the IAC/ISC that was dirty but why would it effect my car only on the highway when I drive 60-70mph ?? If it was the IAC/ISC then it should effect my normal driving on the streets too right ?? And my idle would be high/low too ?? Anyways post up what you guys think the problem could be.....

Oh and the car just recently got seafoamed through the intake manifold only.

[Remy]

My battery is still good I have a battery charger at home and it can't even charged because the batts still fully charged lol my alternator looks fine hopefully it won't go out on me. I'm gonna get the IAC clean and see if that helps. I get bad idle when I drive 60-70 and when I come to a stop going that fast too. All my grounds looks secure too new grounds btw not oem ground wires. I'm staying away from the highway for now I guess...