DSMKilla

Not sure what has caused this but my engine does this surging bit when it's cold out. It only does this on a cold start and at temps below ~60*

COLD START IDLE SURGING VIDEO

I seriously have wayyy too many mods to list so I am not even gonna go there. Basics are LT1 383 stroker, heads, cam etc etc. I do all my own tuning and work so I am very knowledgeable and technical and can respond to any questions for diagnosis.

Things I have tried so far to diagnose...
- Ran a scan with datamaster (didn't see anything out of the ordinary)
- Tried unplugging the IAC (didn't change and surging continued)
- Removed TB and cleaned everything (still no change)
- Checked for vacuum leaks (none found)

Car idles and runs fine once it's warmed up, no surging at all. Even when it's cold it still revs up fine and pulls all the way to redline. It's just been doing this surging thing when it's cold out. It does it whether the ECU is in Closed Loop or Open Loop so it doesn't seem to be a tune issue. Kinda got me stumped so I'm hoping someone could give me a few ideas on some things I can check. I'm sure it's probably something stupid which is why I can't seem to figure it out. It's always the stupid simple things that get me

TwEaKeDSS

dayyyum that thing sounds like a beast

you running a maf or sd? if you still have your maf i would suggest unplugging it and see if anything changes. could be a bad or dirty maf.

DSMKilla

Right on Thanks man

Yeah no MAF here, running in SD Mode.

I keep thinking it's gotta be something with the IAC but I would think that if it was the IAC that the surging would change when I unplug the IAC but it stays the same. I don't know what the hell the deal is.

DSMKilla

Anyone else got any ideas? I know it's not the usual "what exhaust is the best" thread but someone gotta have some ideas

chevy_dude97

do you see anything like fuel related? IDK like maybe when the car is cold u have a leak above the o2 sensor causing a/f to fluctuate? Doesn't sound like you would hear a leak.... :O with that lumpy cam and exhaust.

DSMKilla

Yeah I originally thought of that as well however being that the car is doing this on a cold start while the car is in Open Loop then the o2 sensors would have no effect on a/f enrichment.

chevy_dude97

ok wait... have you tried the temp sensor?

DSMKilla

No because when I scanned the car with DataMaster I watched the temp and it was reading accurately.

chevy_dude97

is it a specific engine temp that it does this? or ambient?

DSMKilla

No just when the car has sat overnight and the temp outside is like below ~60* which obviously has an effect on the temp of the engine etc. Now if it was like summer weather and the temp outside was like ~80* and the car sat overnight and I start it up in the morning then it wouldn't do it. Or if it did do it it would be not nearly as noticeable.

Grinns

could you have a weak battery
alternator adding load to the motor

bobdec

When cold IAC s/b opened up to keep RPM it a little richer, when you say disconnecting IAC has no effect, seems you are idling on TB plate opening (TPS=0) setting and timing w/o IAC control. Are you cold RPM's set up and I assume your closed TPS timing is set up for the cam. Also are the Idle underspeed and Idle overspeed timing advance tables . Are you OBD1 or ODB2 if ODB1 can you post a data log in .csv format or Datamaster . uni format ?

aknight_sa

i had a similar surging issue on my 97 Camaro Lt1, the problem was from the TPS connections.