JakeFusion

iTrader: (7)

So, I've had the car idle tuned and street tuned and was about to take it to the dyno but I've run into an issue where the car does not want to hold idle once warm. My tuner can't get back out to look at the car until Monday, so I'm looking for ideas on what to check/troubleshoot over the weekend. When it was tuned, it idled fine when hot?

Okay, so first things first, I am running in open loop SD. I replaced the MAP because I didn't have it secured on the back of the FAST and it was coming loose, so I thought it was an issue. I bought a new Delphi MAP and relocated to the front and plugged the hole in the back of the FAST. I took the manifold off and when I put it back I double-checked for vacuum leaks.

The car idles fine when cold (around 1050 RPM). But once it starts to warm up it begins to surge from 900-1100 and then it gets progressively worse if I leave it in park or in gear with idle until it dies. It's commanded to idle at 925 once at operating temp.

I've adjusted the TB set screw and reset the TPS several times.

I have a new fuel filter to try. I have a new Racetronix pump in the car.

I plan to take the IAC out and clean it.

I have a new LS3 MAF/IAT in the car. The MAF is disabled but the IAT is enabled.

I had a check engine light come on before I replaced the MAP and it's gone (will have to see what the log shows on Monday if it is MAP or IAC related).

I also plan to drive it today to see if it stumbles/surges under load in gear to rule out the IAC as being faulty.

Any other ideas for what to check? It was doing it before it was tuned. I mean it surged horribly and would die out quickly - and it had a mail order tune on it where it idled fine for about 5 minutes and then never idled right after that. So it's worked on and off and seems to stop working just because.

After the street tune, it idled and drove fine for about 2 hours during the process. Once we finished it had a high idle hang when I pulled it back into the garage. And since then it's been doing this **** while idling once warm. So it sounds like it developed a vacuum leak somewhere that only shows once warm? Because it idles dead nuts when cold.

Any thoughts?

Mercier

iTrader: (15)

IAC is an aggravating little guy. I've cleaned, tweaked, cursed, etc. several IACs I thought were good(or made good by my cleaning and fits) and it always came down to replacing it. They are just so expensive at the parts store. I ended up buying one from someone on eBay and got lucky and it actually works. Problem solved. I also have had cheap throttle bodies develop leaks around the shafts. Looks like you spent the money on a good TB though..but anything is possible.

BrntWS6

iTrader: (7)

I've come to the realization that FAST setups are a bitch to tune right. I've been through my engine several times looking for vacuum leaks etc and It's perfect. It ran great with the LS6 intake while on my H/C setup. I've been back to my tuner 3 times for him to tweak it and I still have some idle hang. Mine seems to be worse when the car is hot too. I've also had it running good while street tuning it with my tuner in the passenger seat, then the next day it will be doing the same ****.

JakeFusion

iTrader: (7)

You have the FAST TB or NW?

I replaced the fuel filter with a new Wix unit. The old one looked pretty new and clean.

BrntWS6

iTrader: (7)

It's a FAST TB. I have thought about trying a NW but it's an expensive gamble. Every time I bring it to my tuner it does get a little bit better, it's just a pain to go back all the time. I'd like to learn how to tune it myself.

01ssreda4

iTrader: (96)

You dont have a mechanical problem. You have a finicky car. Idle and settling to idle can be two difficult and time consuming things to nail down on a street driven car. But, I have to ask, why are you open loop? That means it is NOT using the o2 sensors.

JakeFusion

iTrader: (7)

I know. The tune was done with a wideband. The overlap of the cam will make the O2s read a bit funky. So that was the recommendation.

I do want to try it in closed loop with the MAF and O2s... that might make it worse, though.

ls1 1990 VN

Just a thought,
when the car is well into it's operating temp, if the engine is idling high, turn it off and take out the IAC and see if the shaft is in the 'extended or in' position.
If it's 'in' hold the rubber seal on the end tightish and turn back & forth while pulling the shaft out, should extend out about 1 1/2" to 2"
When extended reinstall, put the plug back on & start the engine.

JakeFusion

iTrader: (7)

Well, I replaced the IAC (the old one was working, but was loose when you jiggled it). The new one is tight. But it still idles up.

On cold starts, it holds idle around 1100. As it warms, it bounces from 900-1100 and then shoots up to 2000 holds it and then starts coming back down to around 1100 slowly, holding at 1500 and then 1100. It's commanded to hit 925, so when it tries to go down to 925 again, well, rinse. Repeat. It just can't find it.

As long as I'm not idling (in park or drive) it does fine. I've been driving it around. I just can't drive in traffic or sit at lights. It stalls out unless I ride the throttle.

Is this a vacuum leak? Is the TB closed too far? What else should I be looking at? The IAC, MAP, TPS, and IAT are the only sensors working in the current tune. All but the TPS is brand new.

SethU

I'm no guru on EFI stuff but have been reading up on Megasquirt/Microsquirt ECU's and came across a similar thread and the solution was in the timing. More specifically, something called Adaptive Idle Control. I don't know if it is something your ECU does or not, but thought it was worth a mention. It may or may not help you out.

Good luck

https://www.youtube.com/results?sear...daptive+timing

JakeFusion

iTrader: (7)

The LS1 has adaptive idle, so that may be an issue. My understanding is it only comes on when the car is not in motion.

I guess the question is - is this a tuning issue or a mechanical one? If mechanical, I need to get it fixed before taking to the dyno. If tuning, it should be fixed on the next round of tuning. I'm just frustrated and not wanting to take it to a shop to have them figure out if it's one or the other. But without the tuning software, I doubt I can adequately troubleshoot this.

rhodes37

Im having exactly the same problem. Im running a fast 92/92 intake and just installed a lq4 in my car. Had the same combo on my ls1 and never had this problem. Now since I installed the 6.0 im getting the same issue its driving me crazy. My tuner played with the tune for two hrs and he tried to fix it by making the car idle high at 1300 rpms when slowing to a stop then dropping it back down to 950. Seems to help at times other times i have to use throttle or throw it in neutral to keep it from stalling. Wont be able to tackle my problem for another 2 weeks though. Please post what you find out. Im going to fill my intake with smoke when i get off to rule out a vacume leak somewhere

JakeFusion

iTrader: (7)

I'm not dismissing the FAST isn't a POS and is leaking. Just seems like it'd show up other than at idle when warm.

ls1 1990 VN

Jake...As I tried before to get you to try checking your IAC when the engine is at operating temp. If it's idling high, take it out, check if shaft is 'in', extend the shaft & then see what it does.
I also believe it's an ECU fix

SethU

When operating in speed density, MAF disabled, I don't think vacuum leaks would cause a surge. Maybe high idle, but not surge. Faulty MAP or IAC are the only hardware items I can think of related to your issue.

I bought a little bluetooth OBD2 reader dealio that plugs into the OBD2 port and shows all the sensors readings in "gauges" on my phone. The adapter was about $15 on Amazon and the phone app was a $5 upgrade from the free version. The app is called Torque Engine Management Diagnostics. May or may not be helpful to you, but is inexpensive and does all the same stuff most other scan tools do, and more.

I forget if you mentioned it already, but sensor calibration for any non OEM sensors. Maybe? I hate throwing **** on the wall. That's all I got.

Burken01

iTrader: (88)

I think its in the tune.

when you cold start it, it goes into "afterstart enrichment" mode which basically means it runs rich for a minute before it settles down..

only problem is it won't settle down, the tuner can data log and rule out stuff fairly quickly.. I doubt its a vacuum leak either, maybe you can check by pressurizing the intake opening sort of like a boost leak tester and see if air is getting out anywhere

JakeFusion

iTrader: (7)

New IAC is in. Are you saying the PCM is commanding it to go in when it should be out? I pulled the old IAC while it was running and it just idled higher and higher lol.

JakeFusion

iTrader: (7)

Yeah. I still haven't heard it lope yet. It never idles down enough.

My cousin was telling me to go buy a vacuum gauge and put it on one of the ports. If it's bouncing everywhere, it's a vacuum leak. But the MAP should show that in the datalog, correct?

JakeFusion

iTrader: (7)

I looked for that. I've got an iPhone and it's an Android app... blah. But I'm not throwing any codes that are displaying on the dash. Also, the sensors... well I bought the same Delphi MAP that the car had. And got the same IAC too. So, I doubt there is a recalibration on them? Plus, it was doing the exact same thing before I messed with either one.

thunderstruck507

iTrader: (18)

Mine used to do **** like that. It was a combination of the Fast brand TB and the RAFIG table it seems. After switching TB and then redoing the RAFIG table it's been fine.

But every once in a blue moon it still will do weird things when idling and get random idle hangs (most notably after driving on the highway, when getting off on an exit it will want to idle high until I come to a complete stop)