Stalling at idle (D) with foot on brake

[Mike St. Louis]

Going down the rabbit hole... daily driver with usual mods- TT , injectors, alky, 340pump hot wire kit, 58/58.

Car was running great until it wasn't. Will randomly stall at red lights and stammer hard under throttle from stop.

IAC jumps from mid 70's to over a hundred and then stall. Sometimes it spikes rpms and recovers.

Numbers while hot in D with brakes

AF 05
L8 32-33
Int 128
Bl 122
Clt 200-204
Ats 95
Rpm 800-825
Tps. 42
Iac 75-82
No Mal's
Idle hot in park numbers:

Af 04
L8 28-30
Int 128
Bl 122
Clt 200-204
Ats 95
Rpm 800-825
Tps .42
Iac 37-45
No Mal's

Any help is greatly appreciated.

 

[1KWIKSIX]

idle Air Control (IAC’s) outta whack
S/B 15-25ish with vehicle in Park & engine fully warmed up (A/C off)

 

[Mike St. Louis]

idle Air Control (IAC’s) outta whack
S/B 15-25ish with vehicle in Park & engine fully warmed up (A/C off)

Thanks, got the tps iac dance down to .42 and 10 pushing the brake pedal dips the iac for a sec and then it stabilized. Cooling fans also bump the IAC when they kick on. Putting it in gear foot on brake jumps to 50ish. Initial studder in gear but stable so far. Does that all sound routine?

 

[THensley]

dose it a\have vacuum brakes ? if so I believe you have a bad booster

 

[Mike St. Louis]

Found my column boost gauge line blew off but I wouldn't imagine it would cause this bad of a problem. Either way fixed that got all my numbers where they should be. Only number that looks remotely out is BL at 118. Started it up, idled perfectly normal, warmed up and drove it a few blocks and it stuttered under throttle from a stop and continues to stutter and stall. Would start back up and stutter again and then come back fine for a block or two and repeat. Got it home, parked and it idles fine. Could it be fuel delivery? I need help...

 

[scgnx2]

What MAF sensor are you running?

 

[Mike St. Louis]

 

[Mike St. Louis]

Looks like a Delco but there are no markings.

 

[scgnx2]

Looks like a Delco but there are no markings.

Yes, I believe it’s an old LT1 version. There very reliable I ran one of those for 20 years before it went flakey. Car began stalling with no MAL codes thrown. Replaced it with the newer LS1 version and solved my issues. I’m not saying this is your problem for sure, but worth looking at. A fuel pressure gauge would be helpful to diagnose a delivery issue as well.

 

[Mike St. Louis]

Went out and tried to start... dead battery. Replaced the battery and the stalling issues seems to be gone. Anyone else experienced this? Not enough umph to power the f pump?

 

[Anthony P]

Lots of odd things or "gremlins" can appear if the electrical system is not supplying the correct > 14VDC when engine is running.

One example I saw while bench testing coil paks and ignition modules. At lower than normal running voltage, spark intensity from coilpak is odd. Using Casper's C3I tool and a spare battery at 12.5VDC, I observed strange, weak, multi-spark for each of the coils. See pic below.



Attaching battery charger to battery and repeating tests with voltage > 14 showed expected strong spark, not the weak, multi-stranded spark seen at 12.5 volts.



Now you have a good, new battery. confirm your alternator output and voltage at the fuel pump hot wire relay.

 

[Mnt86SS]

I had a similar stalling issue. It would die in drive when trying to accelerate from a stop. Turned out to be a stuck lockup solenoid. I unplugged it to confirm (driver side of trans) and no more stalling.

 

[Bescurred]

that maf is a LS1

 

[TireFryer]

Loads of gremlins i had went away after replacing my alternator. I had like 11.8 volts at wot and the whole car was sluggish and didn’t run right. Replaced the alternator and have 14 volts at wot now. Fixed my fuel pressure, intermittent missing, and alky kit not working…