Hey guys I just got this Z28. Here are the specs:

270k miles on frame
at 180k lt1 was pulled, block sent off and rebuilt. LT4 conversion was made (Not really into LT4 though but shes pretty tough ) All GM Performance parts
T-56 was rebuilt, new clutch et cetera.
GM performance custom pcm for LT4 swap
EGR was deleted
Cats were pulled off, leaving rear o2 sensors and egr pulling a code.
Has a optispark 2
stock 3:42 gears
K&N/holley cai setup
BBK throttle body
Corvette Injectors

The problem Im having is, a rough/high idle. I finally had time to drive it today, and check it out but havent gotten it on a lift yet to do full inspection.
@ idle in neutral its running 1100-1200 rpms (normal? I dont think so), I can also tell while driving it is idleing high as well, at 60 in 6th gear im at 1500-1600 rpms. Also while driving if i press in clutch and put it in neutral sometimes rpms dont drop they either stay where they are or even go up (WTF??)
I can also tell it is running rich, i can also smell gas around the filler neck, and when I took off gas cap it was under a lot of pressure???
Also it has flowmaster exhaust w/ no cats, and it is loud but not good loud, sounds kinda sick but someone told me its the stock rectangle z28 tips that make it sound bad.
Also heard belt squeaking and its a new belt, i investigated and it appears that the harmonic balancer is like shaking n stuff not running smooth??

PLEASE HELP ME DIAGNOSE THESE PROBLEMS, bc this is now my daily driver ( i traded a 05 dodge neon for it lol)

 

If it's idling high I'm betting that there is an intake leak(or unmetered air getting in) somewhere. I suppose it could be some type of IAC issue as well.

Is the SES light on?
Have you scanned it yet with an OBD II scanner?

Normal idle is 800 rpm.

Some pressure when removing the gas cap is normal. It shouldn't be blowing out of your hand, but there is a distinctive "sssssshhhh" sound when I crack mine open to fill up.

The rectangle exhaust outlets have nothing to do with the sound. It's the muffler/cats/exhaust manifolds or headers that concern how it sounds. Do you know what series flowmaster is on it? I have an 80 series muffler and it sounds good. You'll hear lots of static on flowmaster mufflers here, but it has not hurt how mine runs(at least with my current setup).

I think it will smell worse without the cats, but I have not run without cats so others without them will need to chime in.

If you are having belt squealing issues it could be the tensioner, but a Goodyear Gatorback belt solved my belt squealing issues(on both my 1996 Z28 and 2005 Nissan Frontier 4x4). If the damper looks in bad shape, do get a new one. It should not be shaking. Is it mounted correctly?

You mentioned the LT4 conversion....do you know what cam is in it? Is it the LT4 cam or LT4 hotcam? Is your intake red or sliver? Do you have a detailed list of parts that were used in the rebuild?

Is the car lowered? It looks lowered in the picture.

 

Yes Its lowered (eibach) and has the LT4 hot cam in it. Im running the AC delco belt on it now, but I work at autozone and we quit selling gatorback belts, do you know if advanced or carquest sells them? Im going to try and tighten down the harmonic balancer today, but I checked out the air intake elbow (stock 90 degree) and it has a tear in the bottom, but its really small. (idleing issue??) So im curious where i can get a replacement, i saw a bunch on ebay etc.. but they dont have a place for the snorkel (do i need it?) SES light is on, but is reading back o2 sens/cat/egr valve. I think Im just gonna dumb $500 bucks and put cats back on eventually, and maybe repair egr if i can. This is my daily driver so Id like it to be more so stock, ( i even kinda wish it didnt have the lt4 swap). But its all good I just need some help solving these issues, before I go throwing money at it.

 

Definitely check for unmetered air getting in. rip in boot, broken vacuum lines etc. You say it has an LT4 swap... do you know how it was tuned or what computer you say was upgraded? as for the egr stuff dont even sweat that crap. it didnt come on LT4's anyway.

I say fix anything you can see and try to get a tune. They can remove the ses lights for the egr stuff and rear o2's.
Mailorder for now with the hotcam tuned in and see if that helps anything. Few of the issues you are having i have also had a couple times and fixed differently. Bad tune was one of my issues, unmetered air was another. Dont just throw money at it either, and a tune cant hurt anything and will give piece of mind. PCMforless or Madtuner are great place to start

 

I got my last Gatorback belt from Summit. Not cheap, but worth it to not have it squealing all the time.

On the balancer, remove the belt, the three bolts holding it to the hub, the balancer, and then inspect it. Also inspect the hub to make sure it is not damaged as well.

Also, read Injuneer's post in this thread as to causes for a high idle.
https://www.camaroz28.com/forums/sho...d.php?t=833545

 

For reference...Shoebox maintains an excellent website for 4th Gen F-bodies.

http://shbox.com/1/4th_gen_tech1.html

Here is a pic of how to remove the balancer with a puller(from his site). Of course, remove the belt first. Oh, and that looks like a Gatorback belt in the picture.

 

the balancer will actually come off without a puller. its only bolted to the hub. however it can get crusted on and hard to remove at times, a nice rubber mallet usually takes it right off with a few swift hits

 

I checked the harmonic balancer today (didnt take it off.. per say), as I thought bolts have backed out a bit but not by much. it was also missing a bolt (wtf?) but i tightened the two bolts and the center bolt down, not to torque spec, but tight enough. I visually inspected it while running and it didnt wobble anymore, but i am curious why there is a bolt missing... wtf?

I checked the air intake elbow, has a tiny rip on outter edge but its not leaking or sucking any air. however their is a vacuum T inserted on top of the elbow with one side capped and one vacuum line running off of it, it came off whatever it was plugged up to when i took elbow off, have no clue what it went to but it didnt change the way the engine ran. I didnt see anymore unhooked vacuum lines, but i did see on the bottom of the motor there what a switch or relay with two vacuum line ends coming out of it, and it wasnt plugged up to wiring harness, instead the wiring harness looked like it had a dummy plug on it?? No idea there...

But what the car does that bothers me is when im driving normally, it runs 1500-1600 rpm in 6th gear at 60mpg (normal??) it idles in my driveway at about 1200rpm and when I take it out of gear while driving down the highway engine revs to 2000rpm and only comes down when i am completely stopped at a redlight or something... THAT really annoys me, and I cant figure out why it is doing that???????

Also noticed after filling it up today, that whenever i hit brakes or anything my gas gauge like moves all kind of crazy around, doesnt hold to true volume of gas. is that normal? i mean like it had a full tank and it would read like below 3/4s when i applied brakes hard to stop. Also dealing with gas tank, when i filled up today and pulled out the hose gas began seeping back out of the filler neck and ended up like spilling about a 1/2 cup of gas on the ground and didnt stop till i put gas cap back on tight. ????

 

IAC valve could be opening when not needed.. TPS i think can do what you described as well

 

Really? I didnt think the iac or tps could do all that? I guess Ill take a chance and replace them just to see if it works or not..

 

dont just replace them. you can test voltage on the tps and also try cleaning the IAC first.. theyve been known to have a few issues when dirty.. i have only had low idle issues with IAC though never high.. i think i had a bad tune when i pressed clutch and rpms went up

 

Im worried that my problem could be tune related, but I am really unsure how I could find out for sure, or how i could fix it if it is? I also figured out where that vacuum line goes on my intake elbow, it hooks into my opti as a vent hose.. ill have to make sure i plug that up tomorrow morning!!

 

Your opti line wasnt hooked up? i musta missed something. Do you know for sure what cam you have and everything? cause if you do you can always try a mailorder tune. Either way its not a bad thing to do for peace of mind and if its not done its a good mod anyway

 

If your opti vac line wasnt hooked up it could've been collecting dirt and anything else to possibly foul it, especially without the line being able to provide the vac to keep it clean.

 

Yeah i accidently knocked off the vacuum line, (the one on the air intake elbow) today when I took it off to check for leaks, but I just went outside and plugged it back up. no harm no faul. took it for a ride, still runs the same so that doesnt fix anything. but im glad i was looking on shoebox and realized thats what it went too, id hate to get excess moisture in there!

The LT4 swap included, GM performance, heads, intake, LT4 hotcam, 1.6 roller rockers, heavy duty lt1/lt4 timing chain, bbk dual throttle body, and corvette injectors.

But what is this mailorder tune? is it worth it to buy a tuner or find someone to tune it? id love to do my own tuning but id be a noob at it. I just want it to run correct idle and fuel mixture bc its my daily driver, it doesnt need anymore performance as of now lol!