Yet another post about stumbling engine at low RPM's

Yet another post about stumbling engine at low RPM's

Postby trapper20 [OP] » November 30th 2011, 11:22pm

Seems like there are 100's of posts on here about vans with this problem, and yet I can't figure out what it is. My van stumbles at low rpms, but when you punch it, it takes off without problems. I replaced the fuel filter, no change. A week ago I had a "Evap control slight leak" code or something like that. Plugs are newer, one wire has a bare spot where it contacted the manifold, but that doesn't seem to be the issue. THe problem has gotten progressively worse over the past couple of weeks. Any ideas?
8" lift: OLV shackles, add-a-leaf springs, shop-made 4" blocks, 5" combo pipe/puck lift and OLV torsion keys. 32-11.50R15 Dunlop Mud Rovers on Cragar Soft 8's.
'76 Chevy 350 with mild cam, 87-95 heads, MSD ignition, headers
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Re: Yet another post about stumbling engine at low RPM's

Postby Phantom » November 30th 2011, 11:31pm

Bad distributor cap ,,maybe cracked vacuum lines , dirty MAF sensor

be sure that plug wire has been moved away from any metal areas and away from other plug wires too close together
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Re: Yet another post about stumbling engine at low RPM's

Postby trapper20 [OP] » November 30th 2011, 11:51pm

Maf sensor, cap and rotor all replaced recently, but dirty Maf sensor is a possibility...what is the best way to clean them?
8" lift: OLV shackles, add-a-leaf springs, shop-made 4" blocks, 5" combo pipe/puck lift and OLV torsion keys. 32-11.50R15 Dunlop Mud Rovers on Cragar Soft 8's.
'76 Chevy 350 with mild cam, 87-95 heads, MSD ignition, headers
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Re: Yet another post about stumbling engine at low RPM's

Postby Phantom » December 1st 2011, 12:01am

Hope you used a high quality cap , the cheap ones don't last

To give official MAF cleaning method I'd have to look it up , but i have used a clean rag dampened with carb cleaner , just don't get any on the electrical part , I have even just removed air filter and wiped the screen off and that helps sometimes

Also could be a leaking injector ir nut kit putting raw gas into manifold , just enough to be momentarily over rich fuel mixture

if you haven't removed the screens in the distributor that can also cause it ,
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Re: Yet another post about stumbling engine at low RPM's

Postby Corsemoto » December 1st 2011, 3:10am

If going to clean, buy a can of the mass air flow sensor spray cleaner at the auto parts store and use that, it's safe and won't risk damaging sensitive sensors. After intermittent P0101 code on medium/full acceleration and so I just removed and spray cleaned mine, let it dry out for a few hours while I did other some other maintenance and reinstalled - no more intermittent code on accel.
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Re: Yet another post about stumbling engine at low RPM's

Postby Sloth Patrol » December 3rd 2011, 3:57pm

when i had my glasspack installed my 99 Astro would do the same thing too. i have the following:

Accel Cap/Rotor
Bosch Platinum Plus
Bosch Wire set
Spectre Air Filter
Cherry Bomb glasspack

before i had the stuff put on my van would hesitate, hard shift, shutter. now i can step on it and roast the tires. whenever it rains my van would continue to shutter but when its all warmed up it is fine.

1999 Chevy Astro Custom Craft 153K. 21mpg.
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Re: Yet another post about stumbling engine at low RPM's

Postby trapper20 [OP] » December 12th 2011, 11:02pm

Took the cap off, all the electrodes had white deposits on them. Cap was only a few months old. That'll teach me to get the economy cap.
8" lift: OLV shackles, add-a-leaf springs, shop-made 4" blocks, 5" combo pipe/puck lift and OLV torsion keys. 32-11.50R15 Dunlop Mud Rovers on Cragar Soft 8's.
'76 Chevy 350 with mild cam, 87-95 heads, MSD ignition, headers
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Re: Yet another post about stumbling engine at low RPM's

Postby Jasen » December 12th 2011, 11:15pm

:whack: ;)
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Every projects a journey man.

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Re: Yet another post about stumbling engine at low RPM's

Postby alexalexanders » December 13th 2011, 2:12am

Ok mine does this to, but i just put new plugs wires cap rotor, all acdelco and wix fuel filter and cleaned the maf. I havent checked vacuum lines but i thought when you had a leaking vacuum line it caused poor mpg? Mines at 20mpg. I do have the common broken vacuum line that causes air from vents only, but i wouldnt think that would cause any running issues correct? Oh ive also run fuel injector cleaner last tank. How do i check for vacuum leaks?
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Re: Yet another post about stumbling engine at low RPM's

Postby chevymaher » December 13th 2011, 2:16am

alexalexanders wrote:Ok mine does this to, but i just put new plugs wires cap rotor, all acdelco and wix fuel filter and cleaned the maf. I havent checked vacuum lines but i thought when you had a leaking vacuum line it caused poor mpg? Mines at 20mpg. I do have the common broken vacuum line that causes air from vents only, but i wouldnt think that would cause any running issues correct? Oh ive also run fuel injector cleaner last tank. How do i check for vacuum leaks?

A vacuum leak would definitely make it run like that.
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Re: Yet another post about stumbling engine at low RPM's

Postby alexalexanders » December 13th 2011, 2:31am

Thank you, whats the best way to check for leaks? Can they be checked from under the hood or do i gotta take the dog house off?


Also, does anyone know if the astro/safari takes the same size vacuum lines or various sizes? Reason i ask is, if they take the same size i may just buy a good amount of whatever size it is and a universal pack of fittings from the help aisle and replace it all. Thanks in advance!
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Re: Yet another post about stumbling engine at low RPM's

Postby chevymaher » December 13th 2011, 2:41am

I am not sure on your year.But I am almost positive the dog house has to come off.Mine does.Just check the rubber hoses for cracking.The boots where they plug in for tightness and cracking also.There are hard lines just bend them if they are cracked they will snap.I had replaced most of the lines a couple years ago.Was messing with the engine and one of the boots just fell off a while back.Replaced it and the idle was alot smoother.You just got to follow them all and check them.I did not have a diagram for it, I just winged it.I have not seen vacuum diagrams on internet or on site either.One of the vans big trade secrets I am afraid.Service manual only place I have not been able to look,don't have one.
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Re: Yet another post about stumbling engine at low RPM's

Postby Jamie » December 15th 2011, 8:45pm

There is a vacuum schematic somewhere here on this forum, don't remember exactly where, I believe it's in the heater-A/C section, I'll look when I get home.
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Re: Yet another post about stumbling engine at low RPM's

Postby Jamie » December 17th 2011, 10:24pm

viewtopic.php?f=43&t=9572
Try this, a good view of the vacuum system
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Re: Yet another post about stumbling engine at low RPM's

Postby Lumpy » December 18th 2011, 4:31am

I've seen several vacuum diagrams for my year. None of them agree.
Vacuum routing varied with where the vehicle was meant to be used.
ie Calif emissions probably demanded one thing, vans in the cold north
another, vans in the Southwest another.

I've replaced my lines. Just took a one inch piece of line to the LAP and
asked for something like 20 ft. Be sure you tell them it's vacuum line.
That's a lot cheaper than something like fuel line.

Then just start replacing ONE hose at a time by disconnecting ONE end,
plugging on the new hose and following to the OTHER end of the old hose.

Pack of those connector thingies from HELP and a bunch of hose only costs
about a burrito's worth of pesos.


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Re: Yet another post about stumbling engine at low RPM's

Postby Wagon Master » December 18th 2011, 10:46pm

The "Check Engine" light was on when I bought my truck, and the prior owner said that the dealer told him it was the EGR valve. I pulled the valve and found it wedged part open because of deposits. Made it run REALLY rough at idle, and would die if I didn't keep the gas on. Replaced it, but I still get that issue on occasion, but WITHOUT the "Check Engine" light. I find that revving the motor generally blows the gunk off the valve and it returns to normal.

Something to consider when running rough at idle, before buying tons of parts.
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