So after changing out TPS sensor, MAP, IAC plugs, wires, cap, rotor and battery. Cleaning throtle body and IAC passages truck still idles like garbage. Checked plenume pan small amount of oil near pcv valve oh changed that too. I have checked every damn sensor on this thing and changed out anything that was even close to giving me an issue. Here are the particulars 98 dakota 3.9.liter 2 wheel drive auto no a/c 161000 kms
only one sensor that I can think of that might be bad is the coolant temp sensor. It was -30 c here the other day and truck had warmed up and had started to cool down 2.5 kohms was the resistance I.e. 60 celcius block was warm but not that hot. Vacuum at idle is 15 "hg no codes, runs good down the road no hesitation even at high idle its fine. Any help would be great thanks

 

Good day,

I had about the same issue. The *%%E?(?*(W%WR*T O2 sensor BEFORE the catalyser, this bast..d dows not give codes unles it is totally wrong, Mine was starting okay BUT after 2 min, it was deteriorating forabout 3 minand than ran okay forthe rest ofthe trip unless i turn it off and back on again...

They are not expensive (38$ a piece ) and while you're at it, replace both O2 sensors (the one beforeand the one after the Cat converter)

Best luck

 

+1 on o2 sensors

 

will give that a try. I will be testing them before replacement as they are like 80 bucks here in Canada. You guys have any input about the coolant temp sensor starts good but then idles drops as if it was already a warm engine. The old owner told me they replaced the water pump I know those sensor crap out if the motor overheats. I think its giving a warm engine signal to the pcm not a cold engine. Any ideas would be great

 

Have you check all your vacuum lines for leaks or any other intake air leaks a vacuum leak can cause your engine to run poorly.
You may have a bad computer CPM I think they are called.
Clogged Cat?
O2?
Coolant temp sensor may as well get it done they are cheap.

 

copy why?

 

I have checked all vacuum lines under the hood the only line i have not checked is the one that runs from the charcoal canister to the purge solinoid. Sprayed intake cleaner around throtle body gasket injectors. At idle and warm engine vacuum is 15" steady does exactly what it supposed to do when throtle snapped open and it also holds steady at about 2500 rpm around 20". I need to check fuel preasure. when I check out o2 sensor for response and the heater I will remove and check to see if cat is plugged

 

Last night checked fuel preasure 50 psi and holding steady compression was good on all cylinders. All sensors reporting data none out of range temp sensor not showing data. Not sure if is a supported sensor or just for the gauge. Still running the same, even my mechanic is stumped. There is also no vacuum leak from the belly pan it actually produces pressure in the crankcase. Any help with this would be great

 

I am working on idle issues on my 98 Dakota as well. I wouldn't replace the coolant temp sensor unless you are not getting heat from your heater and your temp gauge isn't rising like it should to just below half way between hot and cold. Going to try replacing the rear ABS speed sensor. Apparently the computer uses this to help with the idle as well. I have replaced just about everything else just like you. Here is a link to my thread if you want to see what I have done so far:

https://dodgeforum.com/forum/2nd-gen...tage-drop.html

I will update after I test and possibly replace it tonight.

UPDATE: Not the rear ABS sensor for me, yanked mine and tested it with an Ohmmeter, tested at 1.8k Ohms. Would read as open if bad.

My OBD-II tester will give me data on the coolant temp, mine shows it right at 192F where it should be when it is warmed up. If your tester shows the O2 sensor voltages, TPS percent and manifold pressure it should also give you the coolant temp reading, this should be directly from the sensor and then also read out on your gauge on your instrument cluster.

 

I look at it this way if the O2's have never been replace do it anyway same with the coolant temp sensor.

My understanding is the O2 sensors may never show as bad even though it is bad and from what I have read the coolant sensor does play a part in how your engine runs.

If your Dakota has the NTK sensors they should be the originals this can vary but NTK is usually the original sensors.

I just replaced my originals finally these last two months and my Dakota runs way better I never had any warning lights pop up on my dash.