car surges and a/f all over the place

[skaterboy79]

i just installed new heads on my 03 and the car runs fine in open loop i.e if i give the car more then a 1/4 throttle but under light loads and idling it will surge and run like shit when its in closed loop. it feels like a vacuum leak but i cant tell because sometimes it idles fine and other times it will surge between 900-1100 and the a/f are all over the place going from 13.5-18 on my wide band. tried cleaning the maf and reclocking it and no change. also the fan stays on after the car gets up to operating temps. the problem only seems to exist in closed loop. the 02s are original i think and the car has 72k on it. i regularly run 100 octane and 91 with torco but the problem only started after i put the new heads on. my mods are 2.6kb longtubes catted h pipe and steeda cai. the car always stumbled a little before i put the new heads on but not this bad

 

[skaterboy79]

well fixed the vacuum leak but it still has very poor driveability in closed loop and i get a big lean spike when i go into boost. it would even idle then go super rich then die and so i reloaded my tune and it seemed to help the idle problem but still drives like shit under 1/4 throttle. any one?

 

[sprstr1000]

Stock replacement heads?
Ported?

 

[skaterboy79]

stock replacement heads all stock no porting done and stock cams

 

[cobra21987]

Tune issue

 

[03cobra#694]

Sure as heck sounds like a vac leak. You have a vac/boost gauge?

 

[skaterboy79]

no just have the stock boost gauge with the 25 psi overlay. i checked for vacuum leaks the other day and found one at the egr but i fixed that and it fixed the surging at idle but it still bucks really bad until i get above 2300 or so rpms. it runs a lot better when the car is cold but gets worse as it warms up. ill check again for vacuum leaks but i dont think there is anymore

 

[horspla2000]

tune issue

 

[skaterboy79]

are you sure its a tune problem because i drove fine before i put the new heads on and im pulling 20in of vacuum at idle and tried to look again for vacuum leaks but couldnt find any

 

[horspla2000]

Are you absolutely sure your cam timing is correct after the cylinder head install??

 

[IUP99snake]

I'm not sure if you have the EGR, EVAP, and the other emissions stuff enabled or disabled in the tune. If it's disabled, it's just creating a mess under the hood and creating the possibility of a vacuum leak.

When I had my car tuned, I had no idea they disabled all that stuff, but they left all the lines connected. My car was throwing lean codes for years and I pulled my hair trying to figure it out.

I disconnected everything non-essential including the EGR solenoid, the EGR valve, the EVAP line going to the gas tank, PCV system (put breathers on both sides).

Basically, the only things I had hooked up to the vacuum on the intake was the line going to the Fuel Rail Pressure Sensor, Boost/Vac gauge, and Blowoff valve. No more lean codes!!!

It was some random vacuum leak in a system that was disabled in the first place. Most likely the EVAP purge system with the fuel tank...

Do more vacuum checking... take it to a shop and get it smoke tested if you need to. You can do a cheap smoke test using dry ice to pump the system full of smoke. You can also test lines and components with a hand vacuum pump with a gauge on it. You can hook it up to just one component or an entire set of components to see if it holds vacuum. That helped me diagnose a leaky BOV and a cracked hose as well.

But on the other hand, it could even be a vacuum leak in the intake manifold where it seats on the heads. who knows. Get it smoke tested.

Vacuum leaks are such a pain to diagnose. Let someone else do it.

Hook it up to a scan tool and look at the long term fuel trims LTFT for both banks 1 and 2. IT should be within -10% and +10%. If a single bank is outside of that threshold, you know it's a vacuum leak on one side of the intake manifold, or maybe a bad 02 sensor. If both banks are higher than 10% at idle, chances are it's a vacuum leak somewhere else before the intake splits into both banks.

I hope this helps!