Hey all. Please help me. I'm not really new to these forums, but this is my first post here. I'm hoping you guys can help me from experience... I know it's kind of a long read but I'm at my wits end here.

I have a '99 Dakota Sport, 318 Mag, NV3500, 9.25, blah blah blah. The truck is slightly modified, and has 81k on the clock.

Ever since I bought the truck about a year and a half ago, it has had a noticeable idle surge when the clutch is in but the truck is rolling (i.e. only when coming to a stop). It never bothered me much before, so I didn't go to any great lengths to solve the issue.

Lately, however, the problems have grown pretty severe:

First, it usually takes two tries to start the truck. It seems to be worse when the temperature is hotter outside. First thing in the morning it starts fine, after that, the truck takes two or three turns of the key to fire up, and sometimes the RPMs are very sluggish for a few seconds (hovering around stall speed). My ignition and starting system has been gone through twice, so it's not something simple like a starter.

Second, in the past three months or so, I've noticed a SIGNIFICANT power loss through all gears and RPM ranges. The truck overall feels very sluggish and slow to rev. I used to be able to chirp the tires into third gear, but lately it's so bad that if you even try to do a hard launch it feels like it just bogs down. I have 3.92s and an LSD in the back and it will no longer kick the rear out if that tells you anything.

Another major issue I've just now come to realize is excessive oil consumption. This is a BRAND NEW problem. I went on a hunting trip about two months ago, checked all my fluids before leaving, and everything was full. Last Friday I changed my oil after 3,000 miles and it was down almost TWO QUARTS!!! The oil filter was practically dry when I pulled it. I have NEVER run ANY of my vehicles low on oil before. The truck does not smoke and definitely does not leak, so where the hell did all that oil go???

In addition, my gas mileage has dropped to a staggering 11mpg average in combined city/highway driving. Again, the ignition system is fine, the tires are full, blah blah blah. The truck has an aftermarket ECU tune, intake, exhaust, and performance plugs/wires. I do have a heavy right foot, but even so, my average mileage was right around 13.5mpg less than a year ago (with no other changes to the truck).

I've checked the entire truck several times for vacuum leaks, and there simply isn't one.

The truck is throwing NO codes at this point. A few months ago, a check engine light appeared, and when I hooked up my scanner it showed a "Slow/Unresponsive #1 o2 Sensor". I removed the sensor, cleaned it, cleared the code, and it never came back. However, I was getting pretty desperate to solve this problem, so I installed a brand-new pre-cat o2 sensor last week and have noticed no real difference.

I am aware that these engines' intake plenum gaskets are known to go bad. I'm also aware that a few of my symptoms suggest that that may be the problem. IS there any way to tell if the gasket is bad without actually opening it up and replacing it? I have tried "spraying" the area and found no leaks around the base of the intake manifold, but is that a sure way to tell? Any tips/tricks for finding out, and if that's what it is, any advice on brands of gaskets and procedure for changing them?

Thank you guys so much for your help in advance! I'd really appreciate any advice you can give me.

-Josh

 

ya, it sounds like your plenum gasket. just take off the air hat and open up the butterflies in the TB and look down it to see if theres any oil in there, you might need a small mirror to look into the corners. a light coating of oil is normal, but any more then that and you'll have to replace it.

 

Thanks for the input. Any idea how much this will cost and how hard it is to do on your own?

 

I never had to do this on mine yet, but I would guess just the price of some gaskets and acouple hours of your time. it looks pretty straight forward.

if you use the search bar, there are acouple of threads about this.