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93 5.2 Magnum stumbles off idle. I'm stumped #2984599
11/12/21 05:43 PM
11/12/21 05:43 PM
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demon Offline OP
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My 1993 5.2 Magnum automatic has developed an off idle stumble. Last year I had the intake off and replaced the plenum gasket, and did routine maintenance. Drove it for months since with no issues. Lately, it often stumbles and stalls when barely touching the gas pedal. Especially when warmed up, and parking, or going between Drive and Reverse. Doesn't happen when engine is cool. I have removed and cleaned the throttle body thoroughly. Tried swapping the sensors on the throttle body with used sensors from another running 5.2. Replaced the O2 sensor with a new one.
Replaced the PVC valve. Checked vacuum lines. No change. Still wants to stumble and quit. What am I missing?

Last edited by demon; 11/12/21 05:44 PM.
Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: demon] #2984606
11/12/21 06:10 PM
11/12/21 06:10 PM
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mgoblue9798 Offline
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Remove and clean the idle air control valve from the back of the throttle body if you haven't done so already.

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: mgoblue9798] #2984612
11/12/21 06:30 PM
11/12/21 06:30 PM
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demon Offline OP
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Originally Posted by mgoblue9798
Remove and clean the idle air control valve from the back of the throttle body if you haven't done so already.

I have done that twice, and even swapped it with another used one.
But I guess it's possible I have two faulty ones?
When it's out, I can push the plunger in, but it stays in. Not sure if that is normal

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: demon] #2984626
11/12/21 06:53 PM
11/12/21 06:53 PM
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Originally Posted by demon
Originally Posted by mgoblue9798
Remove and clean the idle air control valve from the back of the throttle body if you haven't done so already.

I have done that twice, and even swapped it with another used one.
But I guess it's possible I have two faulty ones?
When it's out, I can push the plunger in, but it stays in. Not sure if that is normal


Next thing I would do is start spraying some starting fluid around while the engine is idling to look for a vacuum leak.

If that doesn't work it is time to find out if it is spark or fuel causing your problem. I am assuming you don't have any error codes when you do the key dance correct?

BTW when you swap IAC's it can take a bit for the computer to adjust. I just put a used on on my 5.9. It was running at high idle for a couple days even after being plenty warmed up, and finally today decided to act right and went into low idle after warming up.



Last edited by mgoblue9798; 11/12/21 06:55 PM.
Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: mgoblue9798] #2984642
11/12/21 07:50 PM
11/12/21 07:50 PM
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poorboy Offline
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My 96 5.2 only has 44,000 miles on it. I got a stumble off idle with it as well. Used air valves didn't help. I finally sprung for a new valve and the problem went away. It was the best money I've spent in a while. It wasn't an original Mopar part (would you really still expect to find real Mopar parts?), so I may have to change it before it gets 25+ years old, but I'm OK with that.

After the new valve fixed the problem, I took a really good look at my original valve. I could see a difference in the color of the aluminum around the plunger in one area. I suspect the aluminum has worn away over time, because miles sure wasn't the cause.

Of course I'm assuming you have replaced the spark plugs, cap, rotor and ignition wires... Gene

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: poorboy] #2984656
11/12/21 08:25 PM
11/12/21 08:25 PM
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Originally Posted by poorboy
My 96 5.2 only has 44,000 miles on it. I got a stumble off idle with it as well. Used air valves didn't help. I finally sprung for a new valve and the problem went away. It was the best money I've spent in a while. It wasn't an original Mopar part (would you really still expect to find real Mopar parts?), so I may have to change it before it gets 25+ years old, but I'm OK with that.

After the new valve fixed the problem, I took a really good look at my original valve. I could see a difference in the color of the aluminum around the plunger in one area. I suspect the aluminum has worn away over time, because miles sure wasn't the cause.

Of course I'm assuming you have replaced the spark plugs, cap, rotor and ignition wires... Gene


I think Delphi was the manufacturer for Dodge. They are available from rock auto. The 12 buck chinese ones though you may as well just flush your money down the toilet and save yourself the trouble.

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: mgoblue9798] #2984717
11/13/21 01:16 AM
11/13/21 01:16 AM
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Change the CRANK sensor, I chased my tail for two years changing out everything, injectors, TB, wires-caps-plugs, mapp sensor, TPS, you name it including the pan under the intake. Never changed the crank sensor because it looked NEW. While getting another TB at the pic a part I got a well used sensor off the 5.9 engine on a whim put it on and has run GREAT ever since. Don’t get Aftermarket crap, get factory parts.
BTW it would run good until a medium load on the engine.
Also changed out both o2 sensors, catalytic converter, water temp sensors, distributor, there’s more just can’t remember all of the stuff.
Now the lock up converter broke, 25,000 miles on a complete trans overhaul. Just about ready to set it on fire.

Last edited by cudaman1969; 11/13/21 01:26 AM.
Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: demon] #2984789
11/13/21 10:05 AM
11/13/21 10:05 AM
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360view Offline
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I agree with checking all the potential problems others have already pointed out,
but you should also check the EGR system
especially if the “pintle valve” bolted to the back of the intake manifold
has never been replaced.

The internals of the pintle valve corrode away, allowing exhaust gas to flow all the time.
This makes it harder for the spark to ignite the air fuel mixture.
This is worse at low rpm and high manifold vacuum - like off idle.

Another possibilty is that another separate part - the EGR Modulating Valve - is turned on all the time.

Why might the EGR Modulating Valve be turned on continuously?

Because those helpful folks at the EPA require that if the OBD-I PCM computer senses any EGR fault whatsoever,
the system goes into “FAILSAFE”
and flows so much exhaust gas that the engine seems “obviously sick”
and the owner will take it in for service.

If you work on the EGR system yourself,
have plenty of new vacuum tubing on hand.
The old tubing gets very brittle and either breaks or cracks developing leaks.
It is pretty tight quarters for the hands working back there, and your vision is blocked by the maze of stuff, including ignition wires.
An inspection mirror combined with a headlight helps.

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: 360view] #2984818
11/13/21 11:16 AM
11/13/21 11:16 AM
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I would look at the TPS,they tend to wear in two areas right off idle and your normal cruising speed. If you have a scanner that can read TPS voltage or degrees with idling just very lightly tap sensor it should stay the same but if worn it will jump. Most of the time it won't set any mil lights. Also ck your set/sync if possible(worn timing chain)

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: SALEM1912] #2984837
11/13/21 12:47 PM
11/13/21 12:47 PM
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demon Offline OP
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Thanks for all the tips guys. I did replace the crank sensor last year, and the ignition parts were all checked back then too. I will check into the EGR.

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: demon] #2984857
11/13/21 02:26 PM
11/13/21 02:26 PM
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I dont think Magnums have a EGR (beer keg intake)

Last edited by cudaman1969; 11/13/21 02:27 PM.
Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: cudaman1969] #2984882
11/13/21 04:18 PM
11/13/21 04:18 PM
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HotRodDave Offline
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Originally Posted by cudaman1969
I dont think Magnums have a EGR (beer keg intake)


The early ones did and i just fixed one doing exactly this by putting a block off plate under it. It was in a van so very easy to see the pintle move, just the very slightest throttle movement and the valve would open all the way up.


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: HotRodDave] #2984917
11/13/21 06:42 PM
11/13/21 06:42 PM
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demon Offline OP
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Originally Posted by HotRodDave
Originally Posted by cudaman1969
I dont think Magnums have a EGR (beer keg intake)


The early ones did and i just fixed one doing exactly this by putting a block off plate under it. It was in a van so very easy to see the pintle move, just the very slightest throttle movement and the valve would open all the way up.


Unfortunately on my W150, it is right against the firewall and very difficult to access

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: demon] #2985029
11/14/21 06:56 AM
11/14/21 06:56 AM
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Originally Posted by demon
Originally Posted by HotRodDave
Originally Posted by cudaman1969
I dont think Magnums have a EGR (beer keg intake)


The early ones did and i just fixed one doing exactly this by putting a block off plate under it. It was in a van so very easy to see the pintle move, just the very slightest throttle movement and the valve would open all the way up.


Unfortunately on my W150, it is right against the firewall and very difficult to access


To diagnose whether the EGR on 1992-1995 Magnums is causing your stumble
you can also disconnect and block the steel EGR tubing that runs over to and connects to the exhaust manifold.

Considering the age and rust of that tube connection,
it might be quicker and easier to just cut the tube
then repair it afterwards with a sleeve or two new fittings.

I have been thinking of experimenting with a “cooled EGR modification:
Using ten feet of corrosion resistant CuNiFer tubing to pick up exhaust gas way back behind the muffler.
The exhaust gas cools in the exhaust pipes and muffler, and would cool more travelling forward in the CuNiFer tubing.
I would use straight lengths of CuNiFer so I could “rod out” carbon build up.

Cooled EGR reduces
pre-ignition,
reduces NOx,
allows use of lower Octane fuel,
and can improve fuel economy.

The brake lines of my 1995 Ram have already been replaced with CuNiFer brake lines 6 years ago.

CuNiFer metal is an alloy of Copper, Nickel and Iron that is easily bent without kinks and is nearly as corrosion resistant as stainless steel.

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: 360view] #2985033
11/14/21 07:59 AM
11/14/21 07:59 AM
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Originally Posted by 360view

Cooled EGR reduces
pre-ignition, [color:#FF6666]as does regular EGR[/color
reduces NOx, [color:#FF6666]as does regular EGR[/color
allows use of lower Octane fuel, [color:#FF6666]as does regular EGR[/color
and can improve fuel economy. [color:#FF6666]as does regular EGR[/color


So what's the benefit of cooled EGR over regular EGR? In a vary narrow arena not applicable to the OP's setup there might be slight improvements in the listed areas IF the computer has the capacity to take advantage of it, doubtful the stock setup does.

https://www.sae.org/news/2014/09/cooled-egr-shows-benefits-for-gasoline-engines

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: Sniper] #2985322
11/14/21 11:50 PM
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Cooled EGR is more detonation resistant as it does not heat up the intake as much as it does on something like the magnum where it picks it right out of the hot exhaust manifold and dumps it immediately back into the magnums already too hot intake.

The other reason I would think would be more important picking it up so far back is that after the cat there is much less unburned hydrocarbons to clog it up, this would save diesel owners in particular a ton of headache as they get clogged with carbon pretty quick.

I still am convinced it causes a drop in MPG cooled or not... you have to pump more volume of gasses through the engine, it is a pumping loss. Also slows down the burn requiring earlier ignition timing witch means more negative work on the crank. Also since the air and fuel molecules are now further apart with innert gas molecules separating them less of them are gonna burn and produce power. I feel it is and should only be considered an emissions control device, every car I have blocked it on saw an immediate improvement in MPG. The only way I could fathom it helping is if your fuel octane level was too low for your engine.


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: demon] #2985344
11/15/21 08:06 AM
11/15/21 08:06 AM
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EGR valve equipped ? If so watch the pintle valve when doing a light / slow throttle up.
Ive seen them go full open on light throttle ( not supposed to btw )
Also has ignition dist been moved.? they need set with a DRB for ignition sync for the system to work right , Been down that road many times with people thinking they can change timing by moving the dist

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: demon] #2985359
11/15/21 08:53 AM
11/15/21 08:53 AM
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When you did your intake did you happen to pull the distributor? If so, wondering if the injection timing is slightly off. I had mine out when I went through my motor and even though I set base timing according to instructions, I had an off idle stumble. Although mine was more when cold. I didn't have a scan tool to read the degrees, but minorly moved the distributor (cant recall which way) and it went away.

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: HotRodDave] #2985715
11/16/21 09:48 AM
11/16/21 09:48 AM
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EGR flow will improve part throttle fuel economy up to the point that % spark missfires have increased, and these missfires lower fuel economy.

Lean air-to-fuel causes the throttle to have to open more, raises manifold pressure, and improves fuel economy similar to EGR,
BUT
more oxygen actually helps reduce spark missfires - the opposite of what EGR does.

Leaning out AFR is therefore better than EGR as regards fuel efficiency, especially if spark ignition has any problem.

EGR lowers NOx more quickly, but if you get extremely lean NOx goes down up there as well.

Both EGR and lean AFR go much better with more than one sparkplug per cylinder.

With one sparkplug, make it an easy to fire off iridium electrode with a big gap.

Re: 93 5.2 Magnum stumbles off idle. I'm stumped [Re: 360view] #2985731
11/16/21 11:09 AM
11/16/21 11:09 AM
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demon Offline OP
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I did not remove the distributor.
One thing though, the engine seems to use more oil than it used to, and it will puff blue out the exhaust when restarted after it stumbles and stalls.

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