i have a 1994 ram 1500 with a 3.9. today i changed the plenum gasket. after i got everything back together it was idling rough. i unhooked the two vacuum lines on the passenger side of the intake manifold next to the pcv port. it seems to run better with the vacuum lines unhooked . what could cause this? map sensor?

 

Check your plug wire routing, and make sure the firing order is correct.

Did you change anything else while the intake was out of the way?

 

valve cover gaskets. thats it. it does seem to run better with those vacuum lines unhooked.

 

That would imply running rich...... coolant temp sensor hooked up good? Keep in mind, you have two.

 

i will check that. i did notice when i removed the vacuum lines one of them was cracked so i fixed it. im not sure if it was leaking all this time and now that i fixed it i noticed the problem.

 

i checked the coolant temp sensor. changed it after i noticed it was cracked. changed the cap and rotor. checked firing order. still idles really low. the idle kinda of goes up and down a little. almost acts like it wants to stall out.

 

Unstable idle is usually a vacuum leak, but, that tends to give you a high idle.

Cleaned your throttle body lately? Sometimes they get gunked up, and the IAC isn't as effective as it should be......

Could try a power balance test. Just disconnect one injector at a time, and see which one(s), if any, have a profound effect on idle.

have you ran the engine enough for it to relearn idle?

Disconnect that battery to reset the PCM after you changed the sensor? (and which one did you change? one wire, or two wire.)

 

i did clean the throttle body when i changed the plenum gasket. it was a 2 wire sensor. i disconnected the battery when i changed the sensor. i have not even put 5 miles on it since i changed the plenum gasket or sensor. should i just try to drive it more? i will try the power balance test. could a bad injector cause that? should i change the iac valve? thanks

 

Having your injectors hooked up wrong would do it too. (its sequential fuel injection, so it DOES matter.) Might be something else you want to check.

You got the right sensor.

It *might* just need to re-learn..... take it for a drive, (someplace not real populated...) and see if it gets any better.

 

i never thought about hooking the injectors back up wrong. i will check those things tomorrow and take it for a drive. do you know the sequence on the injectors?