"need help* diagnosing" 1990 dakota 3.9L 2wd 5sp 160k miles

bought the truck a few weeks ago and its been pretty good so far except for a few problems ive noticed.

the engine idles well around 800rpm and revs ok when you give it alot of throttle but when you open the throttle just a little bit it drops down to around 400rpm up and down, runs rough and almost stalls. also there seems to be more power loss then there shold be driving at low rpm. for example i can cruise around 1300 rpm and then give it some gas and the truck slows quite a bit and struggles before it picks up speed. sometimes it makes it hard to accerate through first gear without jerking. im thinking the two symtoms could be from the same problem.

what i figured out is the egr valve hisses when this is happening and if i unplug the egr valve hose and i plug the vacuum off with my finger (or even let it suck air) the gentally reving problem seems to go away. i can open the throttle a little bit and the engine climbs a little like it should. but hold on, its not that easy. im thinking the egr valve itself might not be bad, disabling it could just be covering the problem up. maybe? because the valve seems to work ok. the diaphram didnt leak when i tested it. it holds vacuum fine and the valve stays open till you take your finger off and let air in. so i dont know where the hissing sound is coming from maybe just exhaust flowing through it? i dont have 60 dollars to gamble throwing in a new one unless im sure its the problem because mine opens and closes fine and doesnt have a vacuum leak. i know it probly should be cleaned, however.

the next thing is at some point someone disabled the check engine light but the computer does however throw up a code like i expected. i have an obd scanner im able to use at work and it came up with "41 alternator field current" but i havent had any problems with my battery or alternator so far.

now this is the thing that probly scares me the most. when i was installing my radio i realized something electrical right around the steering column seems to be missing. thers 3 connectors and one cut wire that obviously used to be plugged into something. maybe i should post a photo?
i did read thers something around there that turns the maintainence required light on so maybe they pulled it out to make the light shut off but could this cause harm like make the computer throw up a trouble code and make the engine run funny? if they wanted the maintance light off that bad i dont know why they wouldnt just take bulb out..

thank you for any replies. i cant seem to figure this one out and i dont wanna go throwing money into it untill properly diagnosed and i just want my new truck to run right

 

things that look new replaced by the previous owner. (seems like they may have had some trouble passing emmissions if you ask me.)

o2 sensor
spark plugs
spark plug wires
distributor cap
coil

i went ahead a replaced the coolant tempature sensor because it was reading the wrong tempature and the fuel filter which was gross and clogged. the tempature sensor actually made it run alot nicer by the way if it failed emissions thats probly why.

 

oh if it helps the cat does need to be replaced. you can hear it rattle when you bang on it but i dont see how that would make it run how i described.

 

first, your cat can most certainly make it run that way. REPLACE/DELETE. second, how do you know someone disabled your check engine light? how do you know the bulb isnt just blown? does it come on when you first turn the key on? third, if you dont need an emissions sticker on your windshield, and you have/have access to a welder, DELETE EGR. the diaphram could be bad, the pipe could be cracked, the gasket on the valve could be bad, or the connection to your exhaust could be leaking. i would also remove the throttle body and clean the heck out of the iac valve hole. unless someone has already been there, its pretty much guaranteed to be clogged full of crap. check throttle position sensor, check map sensor. there are alot of things it could be. start with the simplest/cheapest first.

 

the truck needs to go through emmissions one more time in 2014 before its too old, its a shame. otherwise id be happy to delete the cat. same with egr. ill take the throttle body and egr valve off clean it all up good with throttle body cleaner tonight and replace gaskets and do my best to look for any damage to the egr passage. one thing though does that throttle body have an iac valve? because i couldnt find one the first time i looked. I figured it just has the iac motor that pushes the throttle open to keep idle. correct me if im wrong.

about the check engine light no it doesnt come on at all. ill check the bulb. and the tps is good i checked it with the scanner. it starts at 2% open and climbs to 100% steadily. shame because i thought thats all it was at first. i wasnt sure how to test the map sensor though so ill find out how to test that too.

 

wow i think i just found my problem! taking the throttle body out i noticed a connector not plugged in. turns out its for the the air tempature sensor which is missing completely from the throttle body and the hole is plugged off with some paper!

actually i think it measures fuel tempature? im not sure but after pulling the paper out i realized the opening is sealed anyway. it looks like the fuel flows past the other side and the sensor picks it up. not sure but i am sure having that sensor missing cant be doing anything good

 

on your throttle body there is an iac motor, a tps sensor, and a map sensor

 

finally tracked down the problem it was the egr transducer leaking and it wasnt regulating vacuum to the valve so as soon as the engine came off idle and vacuum was suppled to the transducer the egr valve would stay fully open. found one at a junk yard, threw it in and all is well. also deleted the cat which was all broken up and probably clogged. the engine sounds/runs so much better. now i just need to figure out why im getting trouble code 41