I have a 1997 3.9L manual Dakota with 200,000+ miles on it (from the limited info I received when I got it I believe it is on it's second engine). My CEL has been on and it reads the following codes:

P0300 multiple cylinder/ random misfire
P0304 cylinder 4 misfire
P0306 cylinder 6 misfire
P1294 target idle not reached

In addition to the codes I am experiencing an intermittent hard start. Sometimes it is almost constant and at other times it disappears for stretches of time (up to a few weeks). The truck idles at about 900 rpms which is a little high. While driving the truck I have noticed that the CEL will typically turn off during hard acceleration and will turn back on only when I come to a complete stop to idle.

So far I have replaced the following spark plugs (autolites), plug wires, cap and rotor, and the IAC myself. The fuel pump went out about a year ago and I had that repaired at a shop. I have also repaired two vacuum lines(at the front of the TB and near the fire wall on the drivers side) and a missing vacuum plug under the TB on the passenger side. This has solved the "wild vents" problem that others have experienced. A few bottles of Techron have been ran through the fuel tank as well.

I removed the TB and thoroughly cleaned it twice, with the last time being yesterday. It needed to be done but my high idle persists.

After a little searching on the forum it looks like I need to check the fuel pressure to diagnose the hard start. The fuel pressure regulator will cost about $40 and I am thinking that the diagnostic fee at a repair shop might be a better choice for me as I'm not sure if this problem is above my capabilities. I figured I would check here to see if any ideas pop out to you guys or if I should just take it in.

Searching this forum has been extremely useful and your help has been greatly appreciated.

 

Hi, welcome to the forums.

I wouldn't focus so much on the fuel pressure regulator, yet. You changed it a year ago with the fuel pump. Focus on clearing all those codes.

What plugs are you running - part number? What do they look like? You can tell a lot by there appearance. Check the cap and rotor. Do they look burnt? Does it have brass or aluminum terminals? Are you sure the wires are run properly.

Are you using any oil? It could be a plenum gasket problem. Do you have a vacuum gauge? A vacuum leak can cause the high idle.

You could also try swapping fuel injectors to see if the problem follows.

Lots of things to check.

 

I am having the same issue. Misfire 4 and 6. With the truck off i checked the injector resistance. Should be 12K ohms. Then with it running I disconnected nr 4 injector harness and with a test light went from green and orange to ground and light should illuminate. Then switch to the other lead to battery posisitve and light should pulsate. Try that for 6 also. I am replacing the computer next week.

 

I am using Autolites AP5224. I took the plugs out of cylinder 4 & 6 they looked fine. I tried to upload a picture but the file size was too big.

The cap and rotor did not look burnt but I did find white corrosion inside the distributor cap. They have aluminum terminals. Is the corrosion more likely symptomatic of something or a sign of poor quality. It was replaced within the last year and I do not log very many miles on the truck. I think I am going to replace the cap due to the corrosion, do you have any suggestions as to which cap I should use this time (last time I just used the cheapest cap I could find on ebay)? I double checked the wires and they are ran properly.

I am not using any oil. I do not have a vacuum gauge but do you know of any common locations for vacuum leaks that I should double check?

Thanks again.

 

The corrosion is common especially with aluminum posts.

Try to find a name brand cap with brass terminals, and a new rotor, to match. I haven't bought a cap in ages, the 4.7 doesn't have one. I used to use Standard but that was eons ago.

Spray some carb cleaner around the base of the carb and the manifold, see if the rpms change or if it roughens. Also check for cracked lines, all around the brake booster, etc.

The plugs should be OK.