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Discussion Starter #1
Hi everyone,

I'm helping my father with his 96 LT1. Recently he has noticed it will hesitate and almost die, under really light acceleration, like up a hill or the driveway. It's very faint, and only immediately off idle. Idle BTW is perfectly smooth. No codes present, and otherwise runs like a dream. Local shop said distributor cap needed replacing. So we did all new wires, plugs, and cap and rotor. It doesn't seem as pronounced, but it is still there, and yet no codes. Perhaps someone else with the LT1 motor has experienced this, and could share their insight? Greatly appreciate any help, thanks!
 

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Welcome to the forum.

I have had only (3) Lt-s since '96, currently (2), but pretty straightforward attack. Simply use Advanced Search using, 'Off-Idle Stumble'. There's 3 dots in the upper r. side of the screen, then there you are. Toggle 'Relevance' to 'Date' and Voila!

A few more details to what details you provided will help other first responders more:
-miles, how long pop has had the car
-what search has also been done up til now
-Keywords:
EGR
ICM / IC
Lazy 02s
Intake Leak
Vacuum Leak
Spongy Hose, holed hose, cracked hose, broke hose
Incorrectly Installed "all new wires, plugs, and cap and rotor"
FPR / fuel pump wiring harness
Grounds
TPS
ICM
MAP
MAF
ETC

There's more. The hunt is the excitement. Applaudible you're helping pop.
 

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Hello yourself, and thanks for the info. I'm starting to wonder if pigs are gonna fly, because a suggestion found on the internet, ACTUALLY WORKED lol. It's night and day the difference, not only is the hesitation gone off idle, but acceleration throughout the rpm band seems smoother. As per member suggestion, I took a QTip with some throttle body cleaner across those fine wires in the MAF sensor. Many thanks.
 

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Good news! Thanks for checking back since we keep mental score. But you're just getting started. Find out all the other items up there need attending and "help" your pop spend his money replacing them to make it run "even more perfect." You'll want it in as good a shape as possible when he "gives" it to you....
 

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Word to the wise - they sell MAF cleaner spray, so you don't even have to touch those tiny wires. if you remove the snap ring you can carefully remove the air straightening screen, spray the MAF sensor wires clean, then reinstall the screen.
 

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Aaaaand on top of that intel, it's also been reported no real benefit from permanent 'MAP De-screen Mod'.
 

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Aaaaand on top of that intel, it's also been reported no real benefit from permanent 'MAP De-screen Mod'.
Correct, always always always reinstall that screen, otherwise your MAF readings will be far more unpredictable and part throttle drivability will suffer the most.
 

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Hello yourself, and thanks for the info. I'm starting to wonder if pigs are gonna fly, because a suggestion found on the internet, ACTUALLY WORKED lol. It's night and day the difference, not only is the hesitation gone off idle, but acceleration throughout the rpm band seems smoother. As per member suggestion, I took a QTip with some throttle body cleaner across those fine wires in the MAF sensor. Many thanks.
 

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1996 ImpalaSS WX3
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Correct, always always always reinstall that screen, otherwise your MAF readings will be far more unpredictable and part throttle drivability will suffer the most.
Quick question, if I can take up some of your time.
My 96 ImpalaSS has a MAF without any screen in it.
Is this normal for the 96 ?
I don’t believe the previous owner would have done anything like that, it still had home plate on it when I bought it.
It does have a K&N CAI on it already but I don’t think he would have messed with anything else.
He’s not prone to mechanical endeavors.
Any and all input is appreciated...
 

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My 96 ImpalaSS has a MAF without any screen in it. Is this normal for the 96?
GM never did this before 2001 (I think).
EVERY LT1, L99, and LT4 came from the factory with a screened MAF sensor.
Descreening the MAF sensor was fashionable among some LT1 enthusiasts in the early to mid naughties.
In 2002, among quite a few other more important details, GM descreened the 2002 LS6's MAF sensor so as to release another 20 horsepower & 15 ft-lb of torque compared to 2001.

In and of itself, descreening the MAF sensor is worth almost nothing, and subjects it to turbulent airflow during RpM drops, which can destabilize coastdown and idle til airflow stabilizes.

If a stopwatch reliably measures any repeatable performance improvement from descreening the MAF sensor, the appropriate solution is to install an F- / Y-car MAF sensor, update the MAF tables with Y-car values, and do further MAF calibrations from there. (Someone will eventually buy the B- / D- car MAF sensor.)
Until a free-flowing catback, headers, 1.6 roller rockers valvesprings and pushrods, and a cold air intake with more filter area are ALL installed, it's pointless to descreen the MAF sensor.
 

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I didn’t descreen it, John, the friend I bought it from isn’t mechanically inclined and I doubt he did it, or was aware of such things being done.
I’m going to check back with him and ask now.
My car has had the exact running issues you’ve pointed out with throttling off and the idle returning to its target mark as quickly as it should.
I’m looking at a couple other potential causes for this problem also, I need to take the TB off and do a thorough cleaning, replace the gaskets for any potential air leaks, and perhaps the IAC and TPS.
If I were to consider replacing the MAF with a Y-Body one, is there also any position (1) O2 Sensors that are better (more sensitive) than the stock ones ?
Thank you, all advice and input is appreciated.
 

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Regardless of who descreened it, all that needs doing is, well, reinstalling the screen.
I’m looking at a couple other potential causes for this problem also, I need to take the TB off and do a thorough cleaning, replace the gaskets for any potential air leaks, and perhaps the IAC and TPS.
Probably redundant to mention cleaning the MAF sensor's wires to you (but maybe not to other readers?)
If I were to consider replacing the MAF with a Y-Body one, is there also any position (1) O2 Sensors that are better (more sensitive) than the stock ones?
Without EVERY bolt-on mod between the headlights and the tailpipe tips including headers and 1.6 roller rockers, an F- / Y-car MAF sensor is not worth the time & money.
If the F- / Y-car is FREE, that's another story.

It would be nice if there were any pre-cat O2 sensors awaiting discovery that outperform the OEM ones for us to use.
I'd LOVE to be wrong, but I'd guess that neither OBD1 nor OBD2 LT1 pcm can take full advantage of them, so they're not worth it unless they cost the same or less.
Hope I'm wrong, though. Either way, there remain several things to calibrate in the tune for better MpGs and emissions.
 

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Do you (or any other members) have a spare screen you an part with ?
I haven’t a clue where to get a replacement.
 

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SoCal...

yeah you want the screen. Short of buying a new MAF, maybe "someone" has one they pulled you can get. Its kinda tricky to get them in/out with FU them

If you get a larger MAF like the F-body one you will need to re-program the PCM for it. A stock B body LT1 would not benefit from it though.

or..You can buy the new MAF that has the newer blade type sensor in it and comes with the "adapter" plug you connect to your current MAF wire. IIRC it is also a "Y" connector you also plug the IAT plug into as the new blade type does both functions or just leave your IAT sensor plugged in to where it is now

Cleaning the TB where you take the IAC out to get that area clean is a good maintenance idea. Do not push or pull on the printle of the IAC. The IAC itself may need replacing if you find it sticks in one particular rpm range. This would be difficult to know without having scan ability that shows IAC counts. Most scan tools do not show IAC counts though
 

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Thank you for the response and advice BALLSS !
I think I would be able to feel it sticking by the idle not dropping down as fast as it should, and paying close attention to my tach at the lower rpm driving ranges.
Would you you know the part number for the MAF with the newer blade type sensor you mention in the previous message ?
The idea of trying to replace a missing screen with a used one, that’s tricky to get off or on without F’ing Up the MAF isn’t very tempting.
I am planning on doing the rocker arm upgrade, and toying with the idea of having my intake manifold port matched to my heads, with perhaps some mild porting to the heads and polishing of the exhaust ports.
and CA approved headers.
 

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New MAF's (AC Delco, not re manufactured) are cheaper than used ones from Car-Part.com. Looks like it'll cost you $100 or so either way...

They do have some $30 ones that you could steel the screen from maybe?
 

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Discussion Starter #17
Well I was wrong. Initially, it seemed the problem was solved. But the stumbling off idle is still there. At this point I'm suspecting the optispark ( i only replaced cap and rotor) or the idle position sensor. Of course there are no codes, so I may just be throwing parts at the problem.
 

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Optispark’s don’t usually cause stumbling at idle, or misfires, especially with a new cap and rotor recently installed.
When they fail, it tends to be a catastrophic failure where the car won’t even run.
Does your MAF still have the screen installed in it ?
Sounds more like a vacuum leak or a bad sensor, IAC, Intake Air Temp sensor, MAF sensor bad, dirty or missing the screen.
Any other ISSF members out there with advice, your input will be greatly appreciated...
 

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Discussion Starter #19
Optispark’s don’t usually cause stumbling at idle, or misfires, especially with a new cap and rotor recently installed.
When they fail, it tends to be a catastrophic failure where the car won’t even run.
Does your MAF still have the screen installed in it ?
Sounds more like a vacuum leak or a bad sensor, IAC, Intake Air Temp sensor, MAF sensor bad, dirty or missing the screen.
Any other ISSF members out there with advice, your input will be greatly appreciated...
Hello and thank you for responding. At first the problem exhibited itself with the original MAF, we cleaned that, seemed better for a day or two, problem resurfaced, so we bought a new (Walker brand) MAF, and the problem persists. I hope for the work involved in replacing it, it isn't the distributor. For $26, I'll gamble on a throttle position sensor. 5 min job
 

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A Walker MAF ?
I’m not familiar with it.
If you don’t mind me asking, what did that MAF cost ?
The reason I ask is most members here recommend the ACDelco 213-4527 new style blade MAF.
They are pricey at $139 to $169 but when it comes to MAF’s, you don’t want to skimp on the cost and purchase off brand replacements.
Nor is there any need for the Granatelli or JET MAF’s that go for $250 +.
I recently found a NIB one for $90 on eBay last week...
I hope this helps you.
Please let us know how the Walker unit worked and if it made any difference in the way your car is running.
The IAC (Idle Air Control) can also cause the problems you’ve described and is also easily replaced similar to the TPS, it’s right next to it.
 
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