i have a 91 f-250 351 auto 4 x 4 i just did a tune up i replaced plugs wires cap rotor new air filter (k & n) Now at idle it runs ruff but if i give it just a little gas just enought to get the revs up it runs fine, and it runs really ruff when i first start it up ( if its cold) warms up and it runs better but still ruff. is there anything i can do to correct this problem, this is my plow truck and the snow is starting to fall and i dont want to be stuck out in the middle of a storm some where and it start die on me.. thanks for any help you guys can offer

Rich

 

check the colant temp switch for the computer(they have one for ecm and one for guage) if it is faulty it will keep the engine in cold start mode like keeping the chocke on on a carbed engine good luck

 

could that be the reason that after it runs awhile the heat is hot but the upper radatior hose is still cool to the touch

 

no that sounds more like a stuck thermostat, replace and see what happens

 

just a thought but if someone put a low temp t-stat in the truck that will also make the ecm stay in cold start mode t-stat should be about a 195 deg.

 

i got a 195 deg t-stat just havent put it in yet, if the t-stat is stuck would that make it run ruff while cold?

 

no it shouldn't, first thing i would do is install the t-stat then see what happens, next i would check the temp switch for the ECM. I can't remember where it is at on your truck but the one next to the dist on the intake is NOT the one for the ECM. you can check the sending unit by putting an ohm meter between the plug and ground then write down the reading. Next start the truck and get it up to operating temp and check the resistance again if there is no difference in the two readings then the sender is faulty and needs to be replaced

good luck

 

temp switch where can i find one?

 

do you mean on the motor or where can you bye one.

on the motor i don't know

you can buy one at any parts store just make dure you tell them you want the one for the ECM not the guage