Ls2SilverBullet

Alright guys,

For the past few months I have been trying to get this F.A.S.T. 90/NickWilliams 90mmTB to work on my 98 a4 ls2 z28.

I had another thread a couple months ago: https://ls1tech.com/forums/pcm-diagn...sity-tune.html

Notes:
My car is Speed Density Tuned
I'm using new Fast Gaskets from the lower manifold to head.
Using the old inner gaskets, but they were not damaged or warped, and i added RTV, as you will read)


After swapping the intake manifold from a stock ls1/stock 78mm ls1TB to a F.A.S.T. 90/Nickwilliams90mmTB the car was surging at idle (basically revving up and down between 900rmp and 1400rpm. I thought the manifold was leaking as FAST's are known to so I took it off and RTV'ed between the upper and lower parts to ensure it was not leaking there. So I installed it back on the car, turned it on and it was ECACTLY the same as before.

Since it was the same I figured it was all in the tune so I went in for one. Went to the shop, trying to get squeezed in cuz i didnt have an appt, and ended sitting around for a while. Once the previous customer was done my tuner checked out my car and found my PCV line that strecthed behind the block between the heads was disconnected. He had me hook everything up correctly while they did something else. I also found that a elbow that went one of the nipples that came out of the head was cracked so I replaced it with some hose they had.

After fixing that huge vaccum leak the car seemed to run much better and I got an appointment for the dyno the next day so we could dial in the AFRs and see the new numbers. Took the car to a local carshow and it ran fine the rest of the night.

Next morning on a cold start the car is still surging at idle while heating up. So i drove it around the block and parked it back in the garage and couldnt get it do do it again. Went to work, it ran fine. Leaving work on another cold start its doing the same ****..... This morning was the same

So I'm confused. The "surging" is much smoother and is only 900-12or1300 rpm now.

Is this something else in the tune?

Or do I possibly have some sort of Vac leak on the manifold?

Is it possible for the Intake to be defective, or warped, or something?

I'm going to get back with my tuner for sure, but I wanted some of you guys oppinions/ideas!

Thanks in advance guys!
Eric

moehorsepower

iTrader: (3)

Well if your absolutely sure you have no vacuum leaks it will still be in the tune, Need to adjust a combo of spark, fuel and iac and T/B position. Usually all FAST intakes when bolted on will cause a surging issue when the stockers did not..

98hc4mula

iTrader: (5)

seems like the car needs to be loged for base air flow in cold starts in gear and on park both.
the cold idle tune needs to be looked at. your tuner should know what to do for this.

Ls2SilverBullet

Thats the thing, can say im 100% sure, more like 95% lol, but when I look at everything its all hooked up correctly so from what I can see with the vac/pcv lines they are good.

They will cause a surging untuned, or tuned or what? Please explain

Ok. From what I understand my car will run on one tune until its a certian temp. and then switch off to another tune for normal driving at operating temp. But I'm not sure what that temperature is. And wouldn't I see the surging stop once it hits that temperature?

Now it dosn't stop the surging until after I drive it around.


Thanks alot guys!

moehorsepower

iTrader: (3)

Yes, you set your % of running airflow or idle air at different temps, if it does it only when cold then your tuner needs to log it and adjust only at that temp.

bene

iTrader: (16)

This. Get your tuner look at your idle tune.

Ls2SilverBullet

Appreciate the info guys, thanks

BLK02WS6

iTrader: (2)

Like said above, this - and if it still surges, there are other tables that can be worked to get the surging out, but you are kind of at the mercy of your tuners knowledge...

Ls2SilverBullet

THanks, and yeah, he is reputable especially with fbodies... but this is pretty damn frusterating having to go back. I hope its free of charge or at least minimal since i just (supposedly) got it fixed...

Sprayed1998

iTrader: (10)

Is it fine when warmed? If so my money is on not enough raf at lower temps. Also see if the cars acts better above 140 degrees.

Ls2SilverBullet

Its fine when its warmed up after i drive the car, but it will surge untill i drive it seems like. If I put it in park after a very short drive after warmed up it has a steady idle and stays that way until another cold start

popethe5th

iTrader: (2)

spray some starting fluid or brake clean around the mounting surface of the intake and anywhere else you may think theres a vacuum leak, your idle will increase when the vacuum leak all the sudden turns into a brake clean leak, dont worry its safe i do this in the shop all the time works wonders. or you can buy a $1400 smoke machine and smoke the intake

thunderstruck507

iTrader: (18)

Just be careful using brake parts cleaner, it will eat the paint off anything it touches.