Recently My 01 z has had a stumble on startup... the idlw dips a few times to the point it nearly stalls... also the idle doesnt seem to flare up as much when I start the car as it used to. Once the idle stabilizes the car runs wonderfully, but its an annoying little issue that I'd like to get solved for my peace of mind.

Few details on the car, 01z, LPE 427, longtubes, xpipe, slp loudmouth, vararam intake bridge, blackwing filter. No recent changes to the engine or any other part of the car.

We took a voltmeter to the battery friday and it was hard to get a reading at the battery terminals, when we grounded the meter to the thermostat housing, we immediately got a reading of 12.4 volts (car was off). If I touch the window switches with the headlights on, I can see them noticeably dim. With the car running, my voltage is at 14-14.2, but drops to 13.6 or so when I use the window switch

I have a feeling its a grounding issue, or a battery issue. I'm leaning towards a ground issue because the starting stumble occurs whether the car has been sitting, or if I shut it off and start it immediately. Originally it was a very intermittent issue, but its become more constant recently, though sometimes the car starts without a problem.

You guys/gals have a direction for me to go in or any personal experience with similar issues?!?! Hopfully it wont rain too badly tomorrow and I can screw with it a bit!

 

Nothing to help with but my 2001 started doing exact same thing recently. I like to follow.....

 

My bet would be on a vacuum leak, check the rubber hose on the passenger side front of your intake as its a common place to start leaking.

 

We weren't able to locate any vacuum leaks yesterday in a cursory inspection... I will go over it again today if the weather clears up a bit, otherwise I'll look at it tomorrow

 

in addition, I have had "charge system fault" show up on my DIC intermittently as well, though not recently

 

Cleaned the grounds uner the battery tray... Seemed to make a difference the first time I started it afterwards, but an hour later, same issue... Tomorrow I'm going to clean my maf and inspect all my vacuum lines. If I can't find anything, I'll try a new battery

 

When your car is 1st started up either cold or hot--it is running in "open loop" mode
When cold the coolant must reach apprx 140* before it swithces to "closed loop" ( means it is now running offf the 02's ) When started warm-- The ECM uses a timer usually around 20 secomds before it switches to closed loop
I would 1st clean your MAF- check for intake tract or any vacuum leaks--Also a C5 does NOT have an "idle air control" so when started it only used the throttle blade to control idle speed and fuel--make sure your T-body is clean !!!! With the key OFF the blade should be slightly kicked open--that is normal--be careful when cleaning NOT to bend the blade--It's most likely carboned up -I like to use Brakeclean as it flashes dry when finished
If this doesn't cure it--typically you need to make a small adjustment to your tune--by leaning down the "open loop normal table" in the start-up fuel area--a by-product of your LT headers---Stock commaned AFR is around 13.0 i believe at start-up
-On my car I had to lean it down to 16.2 to get it to start everytime without any issues---

 

Cleaned the Maf, checked for vacuum leaks, tightened down the clamps on the intake really well, and cleaned one more ground point. Things seem to be smoother... not sure if it was the MAF cleaning or the ground issue, but as long as its better, I', happy

I'll keep everyone updated!