GTP dies when slowing to a stop (Vid)

[Bru]

Looking for some pointers on this one.

Last week I changed both drive belts and plug wires (Delco) on the GTP. Soon after, the car started surging when slowing to a stop and sometimes would die all together. RPMs drop down to 300 rpm or so, shoot back up above normal idle and then it dies.

The problem only happens after the car has been running for a half hour or more. It's fine until then but after a half hour the surging and stalling is repeatable. Car fires right up after it dies. Throwing a P102 code randomly. Goes away, then comes back. Mass Air Flow (MAF) Circuit Low Input. Not sure if it's related.

Today I cleaned the MAF, unplugged the PCM to check for corrosion and plugged it back in (seemed OK). Checked for vacuum leaks by spraying down vacuum lines, gaskets and injectors with carb cleaner. Didn't observe observe any noticeable difference while doing so. Vacuum is at 17 inches at idle when cold, though didn't have a T so couldn't check it while hot - tapped into the MAP and it wouldn't run without the MAP plugged in when hot.

Also, at idle, MAF reads 2400-2500 hz. Seems to idle fine, though occasionally seems to stumble ever so slightly. Tapping on the MAF had no change to how the car ran. I recorded some LT fuel trim data but honestly have no clue what it should be.

Click to read more...

 

[Mook]

Gonna also share this in the FB group.

 

[Bru]

Excellent.

 

[smug]

I know you unplugged the MAF then plugged it back in. Try leaving it unplugged and go for a drive.

 

[Bru]

Damn. Good idea. Once it was warmed up and the issue was repeatable I should have unplugged the MAF. Will try that.

 

[Bru]

Almost seems like a sensor problem (not vacuum) because it happens after there's a lot of heat under the hood. That make sense?

 

[TommyGloves]

It could be the MAF dying amongst a handful of things. Can you read the LTFTs when it starts to decel? If they are pegged at +16.4....that would be good to know as a starting point.

 

[Bru]

Will do

 

[SinisterSHO]

I had a similar problem with my 02, felt like I was coming to a stop in a manual car without pushing the clutch in. Replaced maf, problem solved.

 

[Bru]

Nice. I wonder if the NA L36 MAF is the same. My dad has one and I could swap in the new one to test. Will check part numbers.

Edit: Never mind. His is a 98.

 

[Bru]

Looks like I'll also check the O2 sensor wiring against the Pacesetters. Sounds like they could be related.

 

[Bru]

Might have it licked. My guess is the alternator is on its way out. I hooked up a new amp to the existing wiring and 10-inch subs at the same time I messed with everything above. When the engine speed dropped and eventually died, the kick mirrored what the engine feels like when the AC compressor kicks in or you turn the wheel and the RPMs drop slightly.

Today I unhooked the under-hood fuse to the amp and the car ran fine. The RPMs drop when turning dead stopped more than they should, so I'm leaning toward alternator. Going to take it off and have it bench tested and will be looking into replacements.

The good news is that it doesn't die anymore, though there's still a little more work to be done. Also, I cleaned the MAF for the first time ever The car is running like I remember back in the day - Billy, of course drives it now. Makes me miss the damn thing.

 

[Turbocharged400sbc]

how bad was the crud on the sensor fillaments

you just miss all the poon

billy never gonna give it up, never gonna DESERT you

i think i butchered that but it was funny in my head so imma leave it as is

 

[Bru]

James, any alternator recommendations? Stock is the best, stock is the fastest?

 

[Turbocharged400sbc]

Yeah just a stock replacement
if the tensioner could use replacing you could convert to the earlier horizontal bolt bracket and 140 amp Alternator
lots of nearly new alts at aurora yard

 

[Freebeer187]

Glad its fixed. My maf went south and the car would run fine and then totally die when driving. Like an on off switch. Thanks to James who figured it out nealy instantly (and was able to replicate it) I swapped mafs and was good to go.

 

[Bru]

Yeah just a stock replacement
if the tensioner could use replacing you could convert to the earlier horizontal bolt bracket and 140 amp Alternator
lots of nearly new alts at aurora yard

Does Aurora have them on the shelf or do they leave them on the car?

 

[1quick]

Is that the non clutch pulley alt? I have a brand new 04+ and a powdercoated bracket to mount it

 

[Bru]

Just looked up part numbers on RockAuto:

2000
3351078
3342487A
3212168

2004
3212118

 

[greasy]

Last I checked James had about 348 alternators in his garage for the 3800's.

 

[Turbocharged400sbc]

Does Aurora have them on the shelf or do they leave them on the car?

they have em both ways but its cheaper to yank em yerself you'll probably even find a new or newer tensioner bracket. ..idler..you name it...attack rape and pillage. ...

Is that the non clutch pulley alt? I have a brand new 04+ and a powdercoated bracket to mount it

Just looked up part numbers on RockAuto:

2000
3351078
3342487A
3212168

2004
3212118

don't worry about part numbers I have a 2004 clutched alternator on my 97 only because the 97 had a nearly new horizonal bolt alternator and brackets and I wanted them for something else for some damn reason

Last I checked James had about 9 alternators in his garage for the 3800's.

Ficksed

 

[Turbocharged400sbc]

I actually have a spare 140 amp iirc

 

[Bru]

I'm gonna be on the lookout for a stock replacement. Might hit up the yard Saturday.

 

[Bru]

Alternator was good. Put in a junkyard maf and new iac. Seems to be much better now.

 

[02BlueGT]

I was gonna say, those are the exact symptoms I had when my Maf died