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1996 ImpalaSS WX3
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Discussion Starter · #1 ·
I’ve got a new problem with my 96 SS.
When shifting from park/neutral into either reverse or forward gear selection, the car will sputter and sometimes die as I accelerate from a dead stop.
I’ve cleaned the MAF, cleaned the TB, installed new plugs and fuel filter, and the car idles and runs absolutely flawless at all other RPMs and loads.

Is there something in the transmission that could be causing this ?
It almost feels like the converter isn’t allowing the transmission to slip the little it needs to when going from park into gear before the car actually starts to move.
I can put it into gear from neutral/park, and it will still idle just fine, but when I give it gas to move it will stumble and sometimes stall.
It gets better when the car is warmed up but still does it, and only sometimes.
Any and all help or recommendations will be greatly appreciated.
Oh ya, Been offline for quite a while.
I hope all the OG’s are still on these forums.
 

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Freely admitting these are BLIND guesses:
0. recheck again for vacuum leaks between the MAF housing and the intake manifold.
Had similar symptoms, several vacuum hoses that looked ok at first glance, were all brittle rotten to the touch.
Replaced them with various makeshift solutions, symptoms went away.

1. check AIRpump connections.
Although you're forced to keep it there for display purposes, it SHOULD be DISABLED in the pcm(!).
However, if it has not been blocked off from the intake, the check valves may not stay stuck closed.
Note the plug that effectively segregates and separates the AIRpump from the air intake.
Again, be sure that there are no vacuum leaks.

2. Clean or replace Idle Air Control Motor, and Idle Air control path
If the IAC motor is both old AND disgusting, just replace it.
Don't push or pull the pintle.

3. No vacuum leaks? check the ignition driver module, coil, and 9th spark wire.
(Coil-to-opti wire works 8x as hard as the other sparkwires.)
Before you go after the Opti-Spark, check the Vent&Vacuum Harness (Opti-snorkel) and Opti-electrical harness.
And if your Opti-Spark has a Mitsubishi optical sensor, keep it.
 

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1996 ImpalaSS WX3
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Discussion Starter · #3 ·
Freely admitting these are BLIND guesses:
0. recheck again for vacuum leaks between the MAF housing and the intake manifold.
Had similar symptoms, several vacuum hoses that looked ok at first glance, were all brittle rotten to the touch.
Replaced them with various makeshift solutions, symptoms went away.

1. check AIRpump connections.
Although you're forced to keep it there for display purposes, it SHOULD be DISABLED in the pcm(!).
However, if it has not been blocked off from the intake, the check valves may not stay stuck closed.
Note the plug that effectively segregates and separates the AIRpump from the air intake.
Again, be sure that there are no vacuum leaks.

2. Clean or replace Idle Air Control Motor, and Idle Air control path
If the IAC motor is both old AND disgusting, just replace it.
Don't push or pull the pintle.

3. No vacuum leaks? check the ignition driver module, coil, and 9th spark wire.
(Coil-to-opti wire works 8x as hard as the other sparkwires.)
Before you go after the Opti-Spark, check the Vent&Vacuum Harness (Opti-snorkel) and Opti-electrical harness.
And if your Opti-Spark has a Mitsubishi optical sensor, keep it.
Hello Marky. Good to see you’re still here and doing good things for us B body boneheads…
In case you’ve forgotten me it’s David, with the black WX3…
I’ll be in touch with my mechanic, he’s looking at it and if he can’t come up with something definite, I’ll take all the steps you’ve mentioned.
Air Pump was plugged with a kit and when I got the car had dealer do the delete. But I should check on the rubber hose itself along with the other potential vacuum leaks.
I replaced the IAC about 20k ago,MAF about 30k ago.
I’ve got the crazy expensive Taylor plug wires with ceramic boots, but they do have about 60k on them.
Opti was rebuilt at 120k using a Mitsubishi sensor back when they could still get them, 157k on it now. Haven’t been driving it nearly as much these days
So you don’t know of any condition where the transmission could be playing a part in this ?
Thank you for all the tips and advice !!!
 

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So you don’t know of any condition where the transmission could be playing a part in this?
I can imagine it's a possibility, but I've no personal experience with such a thing, and none of the LT1 sedans or wagons I drove as taxicabs for several years experienced such a thing.

Thanks for remembering me.
You're not easy to forget ... and I'll still be around for a while longer ...
 

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First thing that jumped to my mind was the IAC. All of Marky's suggestions are good ones, as well. Try just barely revving the engine when you shift and see if the stumble goes away. That would indicate the IAC.
 
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It's not the transmission. If the converter was stuck on, you'd have a horrendous clunk shifting into gear at idle. And the '96 transmission tends to LOSE lockup when commanded, not gain it when uncommanded. You have some sort of snap-lean happening when you open the throttle.

Suggestions above are good. Also check EGR valve.
 

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Discussion Starter · #8 · (Edited)
Thank you all for the excellent advice and suggestions. I’m going to have my mechanic take the TB off and give it a good cleaning.
the TPS and IAC have been replaced about 20k ago but parts do fail.

The EGR can also cause problems of this type? Would that be due to a vacuum leak or a bad EGR unit or the control valve ?

And Marky, you’re not an easy person to forget either.
Nor you Sherlock. and 91SS, I remember each of you well so to you and the others, thank you for the help.

I’ll keep you posted as to how this issue progresses, and the cause.
 

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Discussion Starter · #9 · (Edited)
Do you know what the exact sequence is for setting the IAC in line and linked to the PCM ?
I’ve seen 4 different ways posted and need to know how to do it for a 1996 WX3.
Anyone ???

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I found it in my Service Manual specific to the 96 SS.
 

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Discussion Starter · #11 · (Edited)
[/QUOTE]
Never mind. I can’t figure out how to CANCEL a post once I’ve started it.
sorry for the confusion.
I’ve got some very different values in the tune that’s in my car from the stock ones.
I’m not sure exactly how this happened but I will be putting the stock tune back in and get things right before attempting to do anything other than compensate for the speedometer.
 

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Discussion Starter · #13 · (Edited)
Alright. I put the factory stock tune back in it to deal with the EGR discrepancy because it was not working properly, but even after doing so the test drive was unsuccessful.
Here’s the really weird part.

My steering when I’m sitting still has a little more resistance turning left, than when turning right.
And causes the engine to stumble slightly when turning the wheel left.
Also, the stumble and stall thing when driving and starting from a standstill ONLY OCCURS WHEN TURNING LEFT….

This miss also happens when in reverse and turning the steering wheel to the left while backing up.
It seems like the power steering system is somehow putting extra load on the engine at low RPMs thus causing the stumble and sometimes stalling.

Is there anything any of you can tell me regarding how the power steering pump or rack and pinion system that may cause such an event ?
Turning the car/steering wheel to the right the car runs perfect and doesn’t miss a beat.

Anyone with information about this issue please, please give me some idea of what I can do to fix this issue.
The power steering pump was rebuilt about 40k miles ago by a reputable hydraulic remanufacture company, but I don’t know how long rebuilt pumps are expected to last.
 

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Check your power steering pressure sensor and see if it failed. I was wondering if this might be the issue. It's on the driver's side next to the steering box.

I'm no steering expert, but if you're having problems one way and not the other, that's the steering box, not the pump.
 

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Check your power steering pressure sensor and see if it failed. I was wondering if this might be the issue. It's on the driver's side next to the steering box.
The switch on the PS line?

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What I would try first is hooking up a scanner and watch the engine RPM at a warm idle (closed loop 180 degF coolant). By memory it should be around 600RPM. Then turn the wheels to right lock and check RPM then left lock and check RPM. At lock the RPM should be higher. Never hold at lock long.

If there was no RPM change at lock repeat the test with the A/C on. Why A/C on? The pressure switch is shown in the diagrams in the A/C section. Some have suggested the PCM increases RPM for high load steering. Some suggest that the A/C has to be running. Most cars just add idle RPM when steering pressure goes up.

If you test at the switch the switch closes at higher pressures IE at lock the switch should be on. You can also back probe at the PCM to confirm the wiring is undamaged.

I'm no steering expert, but if you're having problems one way and not the other, that's the steering box, not the pump.
I am thinking the same way. If the pump is able to affect the engine, and the force required is still high to steer there is a high probability there is a mechanical issue with the steering and the pump is functioning properly.

I would not replace the steering box without checking the steering components. If it requires high effort with the center link disconnected most of us would vote for a steering box malfunction.

Pressure testing would be the only sure way to know if the box or pump is at fault.
 

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Discussion Starter · #16 ·
Sherlock wins the six-pack on this one guys.
But you all offered great advice and tips that all could have been the cause.

Traced back the wires from the pressure switch to the PCM and low and behold, insulation cracked off both wires at the same spot and were touching metal and each other.
Cut, spliced, soldered and shrink tubed the little devils, placed them in harness wire holders and it seems to be all taken care of.

The slight extra force needed to turn the steering wheel left was overstated and something I had forgotten about, but now I recall is something I’ve felt for a while now. Even after having my steering pump rebuilt….

The degree to which it is felt I’m afraid I may have overstated, and may be a mechanical issue.
I think my next big project will be front end steering with all new stuff from center link out.
Any advice on what company makes the best upper and lower A arms ?

Thank you all once again for the great advice, and the time and effort you donated to help me out.
As always….
It is and will always be greatly appreciated !
 

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I put the factory stock tune back in it to deal with the EGR discrepancy because it was not working properly, but even after doing so the test drive was unsuccessful ...
This kind of 'test drive' is typically unsuccessful.
Specifically - a properly executed 'tune' replaces GM's OE bone stock 'tune' in nearly all cases.
This experience has been borne out THOUSANDS of times by the vast majority of mail-order tune clients (who have NOT gotten Keith'd).
 

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Discussion Starter · #18 ·
After locating the wires from the pressure sensor that the insulation had worn off of, and splicing in the repair with shrink tubing and a wiring harness, the Test drive was very successful.
As far as the going back to a “Box Stock” tune, that was done because I didn’t recognize the changes to the EGR that were apparently included in a latter tune addressing fan temps, timing and other stuff.
I believe I may have been messing with those setting and inadvertently’Saved’ them unintentionally.
If you have some time, I still have the tune you helped me build, and would like to flash it in at some point, and perhaps go over some specific changes to the stock tune regarding the EGR…

Thank You for all the advice and help in the past. It’s been very much appreciated.
I do wish I had access to one of Kieth’s tunes, not to copy it or avoid paying him his due course, just to compare things with and get an overall better understanding of how all the different systems intertwine and affect each other.
Does Kieth still offer tunes, maybe I should buy one and have it on hand…

Peace everyone…. And long live B-Body’s..
 
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