3rd Dakota I've owned. 2 1990's and this 1994. The second 90 I modded and was getting over 25mpg on the 3.9, 5spd, 3.55 rear in everyday general mixed driving.

This 94 has an issue though. Right off it got 20.3mpg on it's 1st trip (pleased) withh 3.9 auto 3.55. Not bad for unmodified in any way. BUT...it has a very low and rough idle. I did find that the 2 rear exhaust manifold studs on the driver side are busted at the head, so there may be a connection there? In drive and warmed up it idles between 450-500RPM. I thought to check and up the timing but I see it is all controlled by the computer in this year. DAMN!

Besides asking for the things I should check to get to the bottom of the idle issue, is there any adjustability on this engine for 1994 or any ways to trick the computer?

Thanks,
Paul

 

The bad idle is probably a bad IAC Idle Air Control motor they are bad even when new. Try to clean it up or just replace it. Or you may have a vacuum leak, check all hoses. A good FULL tune up might help as well.

 

Thanks crazy. I will clean the IAT first. Have to look it up in the book....no idea where it is although I'd have to presume in the intake path somewhere. Is there a way to actually check the IAT? I do have all new wires, plugs, cap, rotor, air filter, PCV, fuel filter.

Yesterday I did the 1st mod which was a set of Autolites like I've been modding for the last 20 years and the idle immediately improved a bit with hunting now between 550-600 in drive and improved lite throttle response. In the 90Dak that was worth a SOLID 1.5mpg just doing that. Do it on my Snapper rider and push mower. They both exhibited increased RPM and smoother running. I realize that an exhaust leak will affect the O2 sensor output so have to make that repair a priority. Any idea how deep I can drill the studs before hitting green water? Since they broke either flush or close to flush with the head I can use the manifold holes to hold a pilot guide so I can stay centered. I'm an Engine builder and machinist so that kind of thing is no trouble. I do aircooled VW engines so I am NOT an automotive machinist per se. VW stuff is a different area of machine work. Never did a head stud on a water pumper before and don't want to spring a leak.

Paul

 

I don't know how deep the studs go in, but pull one of the other bolts out and take a look how deep it goes.

 

No way Crazy. It's obvious you don't want to even take a nut off without using the torch to heat it cherry 1st just to avoid breaking the stud it's on. Really you only need to go as deep as 1.5 times the thread OD plus some room for the tap taper.....I guess about 2.5 to 3 times the thread diameter total.