Idle problems 89 4.9L

[Acidbath]

Hey there, i have just recently replaced my vaccum/power booster which was driving me nuts when it was leaking, i replaced it and now i'm wondering if now that i dont have that leak if it is what is causing my rough idle problems. They never happened until i replaced this. Everything electrical has been replaced short of the o2 sensor. plugs wires cap rotor, distributor, and it ran fine before this. Is this a timing adjustment i have to make now? I am getting 41, and 25, which says its running lean, and the knock sensor wasnt detected.. i ran it twice with no other problems the k.s. only came up once. and i got 11's on the KOEO / memory tests'
any ideas? Thanks

[Acidbath]

o2 sensor is now replaced, starts funny, runs fine. half the time it acts like before. so , needles i have a new o2 sensor.

[ModMech]

What kind of idle troubles are you having?

[Acidbath]

well, when i adjust the distributor i can make it do one of two things, i can tell when its retarted enough, to where i'm losing hp, and wasting gas. But it idles and runs fine, with no backfiring or anything. But if i turn it just a fraction counterclockwise i get great HP, but my idle is kinda rough. i've relaced some vaccum lines when i did the booster, so i'm just finding little problems with it now that i fixed some. Anyway, to change the initial timing, i let it warm up, remove the spout connector, then set it to 10 BTDC, which is the "big Tooth" , if im not mistaken? Any info would be helpful. Thinking of removing the IAC, and cleaning it, I have a SHO as well, and that has caused me problems before..

[ModMech]

Idle quality is not affected by the IAC, that will only cause stalling/no-start/rolling idle/high idle.

To be honest, I NEVER tune a 4.9L "by the book", they run much better if you set timing etc. "by ear". Another excellant method is to put a vacuum gauge on the engine (manifold vac. source) and adjust the timing for the highest vacuum. This works very well 99% of the time (leave spout in).

Aside from that, use some etherand spray it near the intake gaskets, you might have a leaky manifold gasket. Also, slightly bad wires can really mess with an otherwise good "tune".

[Acidbath]

Well, it seems when i tune it by ear, i can get awesome HP, but it seems to idle a little off. The more reliable the engine gets the more it seems like its flooding or something, you can hear it miss everynow and then at part throttle, also on start up my idle is questionable until i hit the gas once or twice then she levels off.

[RIGBOSS]

Mine had bad fuel pumps inside both tanks.. tuff to figure out