When I first fire up my '98 after the new tune & smaller injectors...the RPM's instantly jump to 3000-4000 before immediately dying down 1 second later to 800-900 RPM. It idles nicely once it gets that first throttle rev out of it's system.

I removed my throttle body and noticed that the throttle plate is sticking at around 10% or more open at engine shut down. I tried to force it closed by hand, but it springs back to where it was.

I have read that your throttle plate will "stick" at the favorable position your last idle was it. I wouldn't really be bothered so much if it wasn't right at the moment of being started, because the bearings are probably a little dry after the car has been sitting for a couple weeks.

Should I be concerned & what would be the likely cause? I was either thinking maybe the throttle body had been manually adjusted since this car was originally ran huge boost at one time...or maybe just the tune being off a little? I really do NOT want to spin a bearing on a new engine with less than 100 miles on it.

 

all corvette ls1 throttle bodies will be partially open when you remove it from the car. you may have a vacuum leak or the tune might not be good. who tuned it?

 

A tuner from LS1tech. He goes by the name Frost.

It's just intended to be a temporary tune until I am satisfied with the mechanical issues & modifications on my vette. Then I will be soon driving it to a dyno...probably a reputable shop in TX.

I was thinking a possible Vac leak, I am still getting some feint smoke in the engine bay, I am hoping the new 2004 PCV system fixes my problems when my new valley comes in the mail. I assume the smoke could also be leaked power steering fluid, not completely sure yet.

***Edit***

Could an EVAP leak cause this type of high throttle issue, or possibly even feint smoke? I had my EVAP system "re-installed" after I found out it was non-existant. I've been a little skeptical now, since mine was deleted for an unknown reason.

 

talk to Frost, it's probably in the tune

 

Smoke in the engine bay? You do need to locate that and do something about it. PS fluid will flash at something around 385 degrees...don't remember the exact number at this moment but its not something you want dripping onto the exhaust manifolds.

No, your throttle body should not be open that much at shutdown. Most likely in the tune as already suggested. Has anyone ever actually messed with the throttle body itself? I truly don't know if its even possible to manually alter it anyway, just a wild thought.

 

Frost is a stand up guy and knows what he is doing! Give him a call, he will help you.

 

Man, I wish I knew... The smoke is driving me crazy (and scaring me not to drive the car or let it run very long). It doesn't give any indication of being coolant. It doesn't show up in the exhaust pipes. It doesn't appear to be an exhaust leak, and doesn't make any popping noises that a header gasket would make.

I did my best to clean up the power steering & PAG oil leak, and I honestly can't find anywhere on the block where it would have burned. There is definitely no oil burning on the headers. And my engine oil is clean with no leaks. The idle seems to sound fine, It's hard to hear any type of valvetrain noise because of how loud my exhaust system is while sitting in my garage.

The smoke appears after 25 seconds of idling, it makes me think that it is somehow heat related. But almost every internet search I have done has told me the signs point to an incorrect PCV or bad piston rings or a leaking valve seal.

I did a compression check and had good pressure across all 8 cyl, and I didn't notice any smoke coming from the oil fill tube. To be honest it smells like exhaust or burning oil or something.

I just don't know what else to check... I ordered a 2004 LS6 valley cover to go along with my catch can and I am going to cross my fingers and hope maybe it was a poorly sealed intake manifold or an incorrect PCV system.


As far as the throttle body sticking...I don't know the history on my TB, I guess I'll have to take a picture and show you guys what I am looking at.

 

Well, smoke...I suppose you could start with a fan and blow it out and quickly observe where its coming from. I would turn off the hvac so the radiator fans aren't running unless the coolant temp gets way up there, they'll turn on anyway. But should give you enough time to locate the source. Have you gotten the car jacked up and looked for oil dripping onto the exhaust there? Sometimes the oil pressure sender will start leaking and drip oil down the rear of the engine onto the exhaust. Oil pan leaking and dripping oil onto the exhaust or even the rear main seal?

 

YES the throttle is open always at start up--- ( similar to what a GM Quadrajet carb does after start up--The carb cracks the throttle open via the "unloader valve" On a C5 it closes as it warms up as there is NO IAC (intake air control) on a fly by wire T-body so it uses the blade angle for idle air--be extrememly careful not to bend or mess with the blade !!!!

WHY smaller injectors ????? If you changed the injectors you must have the IFR table recalibrated--Smaller injectors would make it run LEAN--if the table is not corrected---
If you car is NOT cammed or has LT's there should be no reason for a throttle flare at start-up---Either a vacuum leak--intake air tract leak or a tuning table that has been changed or not changed correctly
On a cammed car it is typical to have to make several start-up/idle/surging/deceleration tuning adjustments

 

Relax, the injectors that were in there were far too big (48lb) and my engine was stinking up with fuel. I downgraded from a big cam 408 stroker (that was already running too rich) down to a 364ci. I decided against rebuilding a N/A block with -28cc dished pistons and a trashed cam/crankshaft.

You were the same person that recommended that I go with the 28lb injectors for good driveability. I will link the thread if you want

The engine is cammed with LT's. Though I have been fighting vacuum leaks too...i can't rule that out either.

The PCM was tuned with updated setup by Frost, the only guy I've heard of that can actually achieve a fairly close mail order tune on a cammed engine. I wasn't looking for perfect fuel tables....just a tune that I could drive around with and test out my new set up while I work out the mechanical bugs and test out 28lb injectors with a wideband incase I need to change the tune or upgrade to 36lbs.

You have to understand I live in BFE southern oklahoma. There is no tuners within a 200 mile radius that I will trust my car with. And I don't have a truck or trailer to tow it with so I have to be my own mechanic for the moment.

 

Would I be able to see the oil leak from underneath the bell housing looking up? I have inspected everything from the bottom very thorough. I have it on jack stands at the moment.

I am planning to pull the intake manifold off again in a couple days so I should be able to have a full view of any oil leaks from the sender. I don't believe that will be the issue though...I have had the intake off recently.

One thing I should mention...is I changed spark plug brands (from iridium to tr55 copper) and noticed the brand new plugs I pulled out were already stained a black color after 50 or so miles. I thought it was because of how rich the engine was running...but maybe it's oil getting into the intake?

 

Well, are you smelling burning oil, coolant or unburnt fuel?

 

I am not entirely sure, I am leaning towards oil, I know it's not burning coolant...that one is easy.

The smell is not overpowering, just smells like something burning. I am going to try your advice with the fan.