scotty68

I need help... I've been fighting my 1997 LT1 stoker for about a year! It runs great at speed but dumps fuel at idle. I can see the left side LTFT 25% and STFT at >25% after 20 or so seconds at idle. They go back to normal when RPM's raised during driving. The other symptom the car has is when coming to a stop it idles around 2000RPM before idling back to ~950RPM which takes about 10 seconds.

Details about my build:
1997 LT1 / OBDII Computer / T56 Trans
Tune by PCMFORLESS
Howell EFI Harness
Forged Scat Rotating Assembly
Heads and Intake Ported by Golen Engine Service
Comp Cams Intake 236 / Exhaust 242 @ 0.050
Accel 36lb/hr injectors
BBK 58mm Throttle Body
New Optispark / Wires / Plugs / MAF / Temp Sensor / IAC valve
3" exhaust / no cats.

I've done a smoke test on the booster port, no leaks
Replaced the intake manifold gasket and used sealer to prevent it from pulling in oil which it did originally
I've done the throttle body "Drill Mod" where I isolated the idle air so that it flows directly into the intake ports for the idle air. This really helped smooth out the idle speed.
I've replaced header and collector gaskets.

The setup is a swap into a muscle car, so everything has been gone through prior to install in the car.

Any ideas please let me know.

Nostang

iTrader: (4)

The tune is definitely off and needs some fine adjustments. I would contact PCM4less and see if they are able to assist in adjusting the tune. The idle could just be as simple as a table adjustment to the VE tables. The decel high idle problem is pretty common in base tunes. I am sure moehorsepower on this site could help you out as well with the tune if needed and would have much more info on how to fix the tune.

BALLSS

Have the tune looked at.....maybe from someone other than pcm4less

once those adjustments are done and there is still a idle issue scan to see what IAC counts are. They want to be 32 (30-35) at idle, engine at operating temp

did you just drill a hole of random size or did you do it starting at 1/8" and scanning to see what IAC counts are...and making 1/64" larger increments until IAC were right?

atlantadan

There's the first clue.....

scotty68

Anybody have a recommendation on who to have look at the tune? I'd prefer somebody local if possible... I'm in Cleveland, OH.

For the drill mod, I have increased the hole size 3x to what is now 3/16" diameter. I have not really noticed a difference in the way the car idles.

Does anyone know of a scanner that can read IAC counts on OBDII cars??? I have HP Tuners software, an Actron Scanner, and have borrowed a Launch scanner and IAC counts do not get displayed on any of these. If not what is the voltage range and I can figure out the value? I believe the IAC counts range from 0-160 correct?

BALLSS

yes IAC counts are 0-160. IDK if there is a volt correlation. There is on the TPS

My Actron CP9680 does not read IAC either...sucks

My old Auto Tap does which is what I used to do my TB drill mod. I have a old laptop to use with it. Auto Crap does not work with my windows 8 or 10 systems

don't go any bigger on your hole....3/16" is more than most have to go

moehorsepower

iTrader: (3)

You should never have to drill a hole in the throttle blades for idle, especially with that small cam, all this can be taken car of via tune in the pcm...

Viper

iTrader: (6)

scotty68, let me check my mac scanner this week, I'm in Cleveland too.

BALLSS

on aftermarket TB's, like OP's 58mm, on a camed motor many find IAC counts pegged at idle that are 160 and the car won't idle (stalls). Two ways to fix that is

1. drill a hole where the stock TB has one between blades until the measured IAC counts are between 30-35 at idle. Do not blindly drill a hole, have a scan tool that reads IAC (or laptop with software)
2. crack TB open slightly using the stop screw. Then "clock" the TPS back (slot holes) so the vdc are correct for TPS

I subscribe to method #1.

scotty68

I tried method 2 first because it obviously would be a more simple solution... I was fouling out cylinder 5, 7, 8 plugs consistently presumably because air never got to them at idle.

Method 1 has smoothed my idle out a lot.

Anyone else have any idea if IAC counts can be correlated to voltage or what scanner will read IAC counts on OBDII cars?

BALLSS

if you can find a old Auto Tap cable and have the software and an old windows 7 laptop. I bought it way back when and think in general it is crap but at least it does show IAC counts

Check out EasyDiag for iPhone (IDK if they make it for Android to) and get a blue tooth dongle to plug into the OBD port. You have to buy the GM application for it. It does read IAC though

moehorsepower

iTrader: (3)

What works for each individual and what they prefer is their decision, But I have never had to drill holes in the throttle blades for idle and iac, even with cams in the 250-260 degree range. its a combination of the throttle set screw and the airflow tables in the pcm, depending on the software, you can adjust the running airflow, airflow at idle and iac airflow, all of this will get you where you need to be without drilling...

scotty68

I bought the Launch EasyDiag 2.0 Plus... what a piece of crap, but it did read IAC values on OBDII. Good luck logging data with this though it cut out or crashed non-stop.

So the result was IAC = 0 at hot idle. It's highly possible the drill mod hole in the pass through is too big (3/16") but I am thinking I still have a vacuum leak somewhere due to the slow bleed down of idle rpm... it was like this before I did the drill mod.

Anyone know of a way to check for a vacuum leak between the valley and the intake runners? This is where I had a leak before and was pulling oil into the combustion chamber... I thought I had it fixed, but I'm not convinced. Smoke test showed no external leaks.

ILuvPizzaTimes10

iTrader: (1)

sell that BBK throttle body. buy a holley. drill the IAC passage bleed hole. set warm iac counts to ~40.

i had same issue. had it dyno tuned after mail order. then swapped to 24x(for other reasons). all to find out the cylinders are un even due to the iac passage being bypassed with the BBK and most after market T/Bs for LT1. if you look at the back it have a "V" notch cut out that dumps the iac air into the front of the intake plenum. the intake has a shitty low speed velocity. SO the rear cylinders are not getting the same air as the front With the iac passage bypassed. the iac passage has great velocity at low speeds. and all cylinders will be even if utilized properly with closed throttle blades and the iac hole drilled. hope its more then just rambling. and you get what im trying to say good luck.

and the hanging idle is you running off throttle blade input instead of iac air. you need the blades as closed as possible and the iac counts up accordingly.

ILuvPizzaTimes10

iTrader: (1)

https://ls1tech.com/forums/lt1-lt4-m...an-oem-tb.html

scotty68

I ripped my intake off convinced I still had a vacuum leak to somewhere and it appears even after sealing each port oil had still penetrated into the intake runners from below. Anyone know what the best sealer is for around intake ports? I used Grey High Temp RTV last time and although it says oil resistant, it's not fuel resistant and seemed to be degraded by oil.

Sales guy in parts store says Permatex Indian Head... I'm not impressed with that stuff though.

BALLSS

I have always used permatex black "ultra" rtv for intake manifold on front & rear china wall and the felpro "printo" manifold gaskets

atlantadan

Permatex Ultra Black.

Regarding a mail-order tune, I've used PCM For Less, Solomon, PCM Performance and Moe Bailey. Out of all of them, Moe Bailey (moehorsepower@peoplepc.com) is the undisputed master. PCM For Less are nothing more than rip-off-artists at this point. The web is riddled with posts of people being rooked by them. Their glory days are long, long behind them.

ACE1252

Are you referring to the bead of seal that goes along the front and back of the intake?

The Right Stuff.

That is the end all and be all of "RTV" sealers in my opinion. I have never had an intake leak with it....but I've also given it time to cure as well.

The thing that concerns me is you are talking about using it around the runners. If so, don't do it. If the intake gaskets are not sealing, you need to use different gaskets or maybe even have the intake machined depending on if you have had any head work done....and what type....

As far as intake gaskets, I have used nothing but GM intake gaskets. All the other intake gaskets I've seen are crap compared to the OEM units.