Any Mechanics want to lend a hand?

[NTD]

I have a 1988 Oldsmobile Delta 88 with a 3.8L V6.  I bought the car only a month ago, it ran fine then but has developed a couple problems.  At idle it makes a horrible rattling noise(sounds like a diesel ) but the noise goes away if you give it even just a little throttle.  Also sometimes when you come to a stop usually an abrupt stop it will stall.  It does not stall every time but in a 5 mile trip might stall twice.  It does not sputter before it stalls either, just dies....  It starts right back up and runs fine, except for the diesel like rattle at idle.  The Harmonic Balancer has been replaced and I just put in a new Idle Air Control Valve.  Anyone have any ideas what it might be.  The car at cruising speeds runs beautifully....

Thanks guys for any help.

[El Destructo]

Nate...have you got an Autozone near You? If so take it in and let them hook up to the Computer Port...and check for Codes first and see what that may tell you... Could be an EGR Valve Problem...these Carbon up and quit working....could be a bad Cam Sensor....Oxygen Sensor...shouldnt be a Map Sensor...they didnt have them in 88....I don't beleive....but the list goes on....sorry I can't be more specific....maybe Tim Seelen will comment...He is more up to date ...I have not trained in over 12 years now...so as for being on top as a Tech....I am not!

[Josh]

Could be a stopped up catalytic converter too.   

[Pat B]

The rattling sounds like a loose heat shield.

[sailordad]

nate, its been awhile since i have worked on one of them but i will blow out some cob webs and see what we can figure out.
first off i need a little refresher.a 1988 3.8l that carburated correct or is it thottle body injection or multi-port?
if its carburated then i would say the stalling at abrupt stops is more than likely a failed dashpot(its in a vacuum line)
there is a DATA link diagnostic connector under the dash,take a paper clip,straighten it ou then form a "u" with it.there will be two terminals in the diagnostic connector
that are side by side,when you place the paper clip in them with the key on (if your in the correct ones) it will cause the "check engine" light to start flashing
it will flash once then pause then flash twic then pause a little longer and then flash once them twice again(these are numeric codes) it will flash the code "12" 3 times(this is normal and shows its in diag mode)after the last of the code 12 flashes if there are codes in the system it will flahs them out in the same manner,count them and write them down.it will flash each one 3 times(i believe) then go on to the next code.once they have all flashed it will do code 12 3 times again.let us know what codes there are.

as far as the rattle at idle Patb is right on the money there.that is the first thing i would check is for loose heat shields.
what happens when an exhuast heat shiled gets loose it becomes quite sensitive to "harmonic vibrations".these harmonic vibrations change with engine rpm.
when you bring the car off idle the harmonics change and the vibration stops.hose clamps work quit well on exhaust heats shieilds

if it was a vacuum leak it woiuld be more consistant and would run poorly at idle especially on a cold engine.as far as a plugged cat convertor,more than likely not.if that were the case after the engine warmed up you would loose power and would barely be able to accelerate.its possible an egr vlave,but im gonna say at this time doubtfull.these older ones when they fail they usually fail completly and if ythat were the case.lets say it fails in the stuck open position,then it would die at idle al the time as egr gases would be flowing constantly and at idle that will cause the engine to stall.if it fails closed then you would end up with poor accel at cruising speeds and other problems that you havent described.
as far as blowing into or sucking on the vacuum line goes,well it takes approx 17"-21" of mercury to pull enough vacuum to pull that diaphragm.if you got that kind o fpower i wan meet your sister  ,beside you realy dont want to be sucking on a rubber vacuum line that has had years worth of carbon and petroleum vapors goinf thru it.not just unhealthy but it leaves some serious black marks on your lips to boot.

let me know whats what. o.k.
we will get this figured out for ya
                                                                     peace,
                                                                           tim

[El Destructo]

If you can't figure out the Paper Clip Trick Nate...AutoZone has the Keys for the older Vehicles too...they can plug it in and read the Check Engine Lights for You also...as for an 88...they were Throttle Bodied....the 3.8...or 3800 both were ...and are very good Motors...I have a 91 3.8 in a Grand Prix...and a 3800 in a 2000 Grand Prix...both exceptional Motors...and Josh is Right about the Converter wreaking Havoc too...might want to let someone else rev the Motor slowly and You listen to the Tail Pipe for the Telltale hissing sound...I know when my 91 Chevy Van's stopped up...it ran like shit...and when I beat the Crap out of the Converter with a 4 pound Shop Hammer...it now Purrs like a Kitten again! The only trouble I had with either of mine was a clogged EGR Valve...and I was lucky...I cleaned out all of the Carbon ...and reused it

[NTD]

Wow   Quite the responses guys I appreciate it.

Mike (El D) is correct it is a fuel injected engine.  And the reason I bought the car is exactly because of what you said the reputation of the Gm 3.8.
Autozone told me that unless the check engine light is on they won't get any codes.  And my check engine light isn't on

There is no black smoke.

Scott D, it idles fine, just rattles...just like a diesel.  Also the rattle stays through out all gears including park but it stops the short time between shifting through the gears.  I will check the hose to the EGR valve and don't worry Tim, my lips won't touch it...I've got an air compressor

And thanks for the advice on the heat shield, I will check that tomorrow.

Thanks again guys.  This is my only air conditioned ride and well with 105 this week....AC is nice.....

[Badger]

  Another possible simple fix that I run into commonly with throttle body injection is that right at the entrance to the throttel body where the butterfly is a slight carbon build up there will cause rough idle and dieing. It can simply bewiped out with a rag with a little brake clean or laquer thinner on the rag. Steve

[Pappy]

Never ran many 3.8 but have had 25 or 30 4.3's in our fleet and the main trouble we had with all of them was the egr valve got carbon build up under the valve and held it open witch will cause just the kind of problem you are talking about.That would be my first check.When it hangs open it creates a huge vacuum leak.
    Pappy

[Justin Snyder]

Like Pappy I never had a 3.8, but I have had a few 2.8 and 4.3.  The EGR valve is where I would start also. Then check the heat shield right below the spark plugs.

[aero86]

if it rattles like a diesel, sounds like knocking..  that maybe from too low idle.  have you tried seeing if the throttle plate is dirty?  that can cause a stalling at stop

[NTD]

Okay some updates.

I pulled the belt off and the noise went away.  Ruled out that it's any part of the engine.  Listened around with a screw driver and think it may be the tensioner pulley.  But it's still dying and now not always at idle.  It seems to die more often on turns though.  Maybe a fuel pump/sensor or something??

[Badger]

NTD, when you pulled of the fan belt it may have just made the motor run a tad faster smoothing it out. So you may have not eliminated anything. If it were a pulley it would get louder as you accelerated the engine. Proably something loose like a heatshield as suggested. Have you tried any of the suggestions allready made such as your pcv valve or throttle plate being dirty. Several of us here are proffessional mechanics and see these problems all the time. Steve

[aero86]

take the intake tube off the throttle body.  if the plate is dirty, it needs to be cleaned.  get a shop rag and some carb cleaner.  but a brick on the gas pedal, motor off of course .  spray just a bit inside the throttle body, and wipe out.  repeat that till you get it really clean on the bottom and top of the throttle plate.  make sure you get clean were the plate seals inside the throttle body.  be sure not to spray too much inside the motor. 

[Voodoo]

Had a few of these olds in my family with 3.8 or the 3800, the diesel noise might be coming from a tray under the intake, it's pretty common, and a lot of cars were brought into the scrap yard because of it where I was a wrecker driver............take the intake off, it the tray is loose .. replace it, the noise will be gone.... and check the egr first, then cam sensor, and don't forget to get a pressure test on the catalytic converter.....