Hi everyone! I've been driving my new (to me) 03' Vette for a few weeks now and have been loving it! However it does do one thing that kind drives me nuts... it's not every time, but about 33% of the time when I start the car it will turn on and then idle down reallly low, like almost to the point of stalling, it doesn't ever stall but it gets really close, like maybe 200 rpm. Then it will rev itself up to about 1k and after about 4-5 seconds it normalizes and it's good to go.

Now here's the thing, the car has been modified, it has a cold air intake, headers, catback exhaust, and cam with a tune (makes 370 to the wheel, PO provided dyno sheet). I bought the car like this.

I don't know if it's the tune, maybe it's just a bad tune on it, sometimes I can small gas (like its running a bit rich). So i'm not sure if maybe I should get it dynotuned by someone, or is there a part that should be replaced? Thought about doing a full tune up (spark plugs, plug wires, PCV valve, oil change, air filter change. But i'm not sure if that will make a big enough difference...

I've also been toying with the idea of getting rid of these modifications... surely they are worth something to someone, but if the car is going to behave like this then I have no problems with setting it back to stock...

Car has 60k miles and is a Manual. Also the CEL turned on this morning, not sure what its for yet.

 

Do you know how to read the DIC codes? you could start there.
When you start the car turn the key to on for 1 or 2 seconds before starting to let the fuel pump prime and see if that makes any difference.

 

Things you can do yourself that won't hurt:
- find out what the CEL is and address that
- run it down to 1/4 tank, throw in a bottle of Techron or Seafoam, run it till the low light comes on. This is an effective way to clean the injectors.
- clean the throttle body / throttle body plate. It gets gunked up over time on all cars and can cause start/idle abnormalities.
- won't hurt to at least check the spark plug wires, plugs etc.
- check & clean all the grounds (sticky is on here somewhere)

If it still has symptoms, find a competent tuner & tell them you want a start/driveability tune. Tuning for WOT is relatively easy. Tuning for smooth cold starts, part throttle smoothness etc is hard. It'll likely cost $500+

good luck!

 

Thanks! I'll definitely try what you suggested... I just went and read the code and it came up with "10-PCM P0153 H C"

I googled it and it said that it was an o2 sensor, I guess i'll have to replace it first then go through your diagnostics.

 

that could be your problem.

 

Well I didn't have any TB cleaner but I wanted to see the condition of it anyway, I looked at it and honestly the Throttle body looked pretty clean already. I'm still going to remove and clean it but at first glance it seems good.

I did try turning the key and waiting a few seconds before starting the car and it seemed to start a bit better, so maybe I was just starting it too soon? I don't know either way I'm going to fix the CEL and clean the TB's give it a good tune up and then go from there... a tune is probably in my future.

 

Don't need special cleaner, just wipe it all clean with a paper towel.
It is a good thing to routinely turn key to Ignition, let the gauges do their dance, computers fire up etc. Give it a couple seconds then actually start the engine.

 

It's just weird how inconsistent it is, it happens hot and cold. I tried letting the car sit for a couple seconds before starting, it seemed to help some but it still does it from time to time. If it were the tune then wouldn't it do it all the time? Idk, today i'm taking the TB off and cleaning it, i'm ordering some spark plugs as well and i'm going to replace those. I'm going to try that seafoam trick and cross my fingers as well. I cleared the CEL and it hasn't come back on (I've driven about 300 miles so maybe it needs longer). Also I was thinking should I replace the PCV valve? Maybe not because the idle isn't bad it's just the start up and it's inconsistent and random.

 

Little bit of an update, I cleaned the TB and the problem persists... however I noticed that it only does it when the engine is warm. I looked it up online and people said it could be a stuck EGR valve or an oxygen sensor possibly... funny thing is I was getting that code for the O2 sensor so maybe that's the problem... It only does it on startup though, not when it's warm and just idling. I have to turn the car off, then start it back up, the car will idle really low to about 200-500 rpm and then slowly "catch up" back to about 1-1.2k rpm. I noticed that if I try driving the first 20-30 seconds the car will almost want to stall, more revs are required.

Weird.

 

Fix the O2 issue then cold-start tune.
I doubt the O2 has anything to do with it, car is running closed-loop on startup

 

Engine is running in “open loop” for at least 30-45 seconds upon initial startup !!

 

Any reason why it would only do it when it's hot though? The car cold starts fine everytime, only when it's hot it does it.

 

Sorry you are right - I got it bass-awkwards

 

When the car is first started it is running in “open loop”...the fuel trims are NOT active at this time...if the car is running lean (low O2 voltage) you won’t see that on a scan tool until that time...your fuel trims will be elevated...you’d need to get a scan tool on the car and see what you have...anything over +10% is of concern !!..also negative fuel trims at of -10% can be bad...PCM is subtracting fuel and may be your fuel “smell”...may be dirty air filter...you will see negative fuel trims with a dirty air filter...educational video below !!

 

I have an OBD2 reader adapter for my phone, do you recommend an app that can see fuel trims? I'll definitely look those over if I can. In the meantime i'm going to remove the air filter and try cleaning it. It does appear a little dirty on the outside (although nothing crazy).

 

I use scan tools so I don’t know about these apps !!

 

Which scan tool do you use? If it's not too expensive i'll spend some $ and get it.

 

I have 3 right now...GM Tech 2, Autel MS906 and a Snap On Verus Pro D10. I’ve had members send me data logs from HP Tuners...10 pages long...LOL !!...or a data log from the Torque App...don’t like to look at gauges !!...just show me data PIDS with just numbers and all on one screen !!

 

over 200 bucks for a scan tool.
Many out there but not familiar with these tools

 

did this ever get figured out?im having the same issue with a 2017