Long story sorry…

I have a crate ls3 480/376 in a 99 miata. Ran 3.5k miles last year with no problems. This spring i had my driver side header modified to give me a bit more clearance around the column. Header looks identical except for a one pipe was modified where i used to have it bent in. While i was changing that i changed the plugs and installed a new air filter. I also had to loosen up the driver side knock sensor and so i could rotate it. While i had the header off i had the battery disconnected which was for a couple weeks.

Now the issue. I started it up and it will not idle. Barely runs and stalls if i don't keep on the gas. I drove it roughly 10 miles that way hoping it would come out of it but it didn't. The strange thing is if i am above 15 mph with the clutch in or clutch out in neutral the car idles perfectly. Soon as the speed goes below 15 mph it wants to die. The VSS is connected and i am getting my speed reference from the gm computer. While driving it wasn't running great but it was drivable.

I changed the plugs again last night because i put tr55's originally gapped at .50 and just because it was easy i put in tr5's with the stock gap (checked all though)

Seemed the same but i only tried to idle it i didn't drive it or disconnect the battery to clear anything. Last night i did disconnect it and i won't be home until later today to try again. The intake all looks tight so i don't think air is getting in from some place else. Everything i unplugged i rechecked to make sure i plugged in. I don't know if some how i killed the o2 sensor on the new header side. I don't have a scanner or a tuning program readily available and i didn't check to see if the engine light was on (not on my dash).

Any ideas?

 

I`m also interested in the answer to this problem, from someone running this engine/PCM

 

If you're running a MAF, start checking your fuses. Sounds like the fuse for the MAF has popped (labelled gauges I think?)

 

just got home and checked. All fuses good in the gm fuse box. reconnected the battery, turned the key on and the check engine light is on like it normally would be with the car not running. Start it and the light doesn't come on but the car still dies, light didn't come on after it died but i know the light works and that is the idiot light in the gm crate fuse box.

EDIT: alright, i just unplugged the maf and it idles fine. So my question before i get cleaning the maf does it go into another mode and not use the o2 sensors? My only thought is maybe the oil from the new filter screwed it up?

 

Sounds like you got your MAF covered in oil. Without the MAF, it reverts to a "safe mode"...but it still references the O2 sensors. Go grab a can of MAF Cleaner at A***zone and give it a thorough cleaning, let it dry, hook it back up without the filter and see if it's any better...

 

Bah i thought that was going to be it. Pulled the maf sensor looked clean, got a can of maf cleaner, cleaned it same thing. Pulled it again, cleaned it again. Same thing.

car still idles when i pull it. So either the maf is dead after 3.5k miles or when it goes to safe mode it covers up the real issue.

 

Did you change the just the filter (same type), or the entire style of filter to something different. Is it on the stock GM (crap) tune that comes with the LS3 480. I spent hours and hours getting one to idle in a 79 TA last week all because of how they had the MAF mounted in the tube. The new blade type MAFs are extremely sensitive to what you put in front of them and the size of the tube. You might consider putting one of these air straighteners in front of the MAF. https://ls1tech.com/forums/generatio...ighteners.html I bet it would help. And if it is on the stock tune that comes with the crate motor, work on the tune.

 

it is still on the stock tune, intake piping is the same as it was before and the same exact filter just new as i ran all last summer. I am trying to get it to run correctly so i can make the 2 hour drive to slowhawk for a real tune. I could trailer it but i don't want a 4 hour round trip if something is crapped on it.


when i get home tonight i am going to try and put the old filter back on. See if that works, if it does then i will just put the new filter on when i get down there.

Edit- I rechecked everything again. Didn't find anything, started it up it, stalled. held the rpm's at 1400 and let them slowly come down until it idled on its own. Now it is running great. who knows