Hello everybody I have a 93 5.2 V8 Dakota. Having a few minor issues with it, such as rough idle from time to time, sometimes accompanied with a gassy smell, like it's running rich. 9 times out of 10 I shut it off, come back a few minutes later and start it up again and it will idle fine, or it will gradually smooth out. When warm it idles at 400 rpms, though especially with the rough idle it seems to dip a hair below that. A couple years ago I would swear it idled at 600 rpms. And it could be in my head, but it feels like it's lost some power that it used to have.
The other odd thing is my airflow; when I accelerate up to about 50 mph the air flow redirects to the defrost and then returns to the front vents after I let off the gas. Even opening and closing my windows reduces the air flow by about 50% and returns to normal flow the second I take my finger off of the button.
The least concerning problem (I think) is my antifreeze. For maybe 18 months or two years now my antifreeze gradually disappears out of my reservoir. No leaks, no puddles and my radiator is always full. But I can top off my reservoir every two weeks. And my oil has always been clean.
I've had several things replaced over the last year, including a new heater core, fuel pump, fuel filter and line, battery, and ignition coil. Maybe a vacuum leak? I haven't looked at the spark plugs yet. If anybody has any ideas or experience will these problems, let me know I appreciate it. - Cheese

 

Each of your issues separately would be different problems but together I suspect you have a leaky intake. Your idle should be around 600-700 rpm. 400 is definitely too low. Defrost is a default mode for your vents when vacuum gets low. As to coolant loss, I believe these engines use coolant through the intake. Taken together, the coolant is dripping inside the engine and going out the tail pipe. That same leak is allowing air to leak in where you want vacuum and it's causing the engine to idle slow. I'll bet your fuel mileage has tanked too. Are you using much oil?

Unlike later models, it's fairly easy to work on this engine. Have a shop do a plenum repair and that should take care of the other problems too. It's possible you have a cracked intake, but not likely. There is a thin metal shield on the bottom of your intake. When it starts to leak, you lose a lot of power and use a lot of oil. This definitely needs to be repaired as it will only get worse.

 

It doesn't use oil, or very little anyway. I've only added oil to it twice or maybe three times in six years and it was never very much. Thank you!

 

Then your plenum may not be blown. How many miles on the engine? Your intake may just be a little loose. Personally, I'd tighten the intake bolts just a tad. They don't need to be super tight, Factory torque is in inch pounds. If it helps, the intake will still need to be pulled to fix it properly, but you should have some time. Don't put it off too long. Would you rather work on it when it's 80 degrees outside or 8 degrees?

Before you do anything, I'd slap a vacuum gauge on it just to make sure. A healthy engine should pull around 17 inches of vacuum but a worn might be a little lower.

 

Around 135,000 miles. Now that you mention it I remember now I had something done with the intake. I can't remember if the intake itself was replaced or the plenum or both. But something was done with it maybe 3 years ago or so. I need to write this stuff down so I know for sure. Yeah, I'm trying to get everything in tip too condition before fall

 

My '96 Ram was showing 168K when I blew out the plenum. I did a major tune up when that happened. It had been reading high for a long time and when I tore the engine down, the timing chain was still good but looked like it had around 150K on it. I didn't pull the heads or exhaust manifolds but everything else on the top and front came off. I fixed my plenum, replaced a leaky oil sending unit, cap, rotor, plugs and plug wires, new injectors, new timing chain and water pump as well as replaced a failing harmonic balancer. I've got an engine now that purrs like a new one.

You may not need that much work but have someone check for slop in your timing chain. By the 1990's, metallurgy got to the point timing chains lasted long. Your intake may just need retorqueing.

I replaced a bunch of stuff that didn't really need replacing but I was in there anyway. I also found the ticking sound that had been in there since I got the truck several years ago. I found several oil soaked cigarette butts and a flattened can of Schlitz beer in the valley under the intake.

 

Oh yes I forgot, my oil pressure gauge, when warm, has the needle barely in safe most of the time. Not very long ago it used to be close to half way in safe. Maybe it's just the gauge, as my fuel gauge doesn't always work perfect even with a new sending unit in the fuel tank. Maybe it's related to that too. I wish I could take it all apart myself but I don't have the space or tools haha

 

On the Magnum engines, the oil sending unit is on the back right next to the distributor. On the 1994 up Rams, it's a stinker to get to. On the Dakotas like yours, it's not too bad. You can reach back and feel if it's oily and maybe wiggle the plug a bit and see if that makes a difference. It just sticks straight up from the block.

 

Oh perfect. Dang you did a lot of work to your truck, it would be cool to be able to basically rebuild your engine.

 

I haven't rebuilt an engine in years. Elderly eyes, hand tremors and so on make it nearly impossible. On the other hand, the major tune up I expected to take a couple of weeks actually took nearly 2 1/2 months. I found broken bolts in the heads to drill out, failing parts that hadn't failed, yet, and I had just retired and it was a hot summer so I didn't push it as hard as I would have when time was short.

At 135K you still have a solid engine that may just need some attention. Find a small shop and have them do a vacuum check and see what all you might need. I suspect you might just need the intake retorqued. Don't tell them the problem, just detail the symptoms. That way they will look and not just throw parts at it.