Hello newbie here with a few problems..2 weeks ago i bought a used 99 ram 1500 quad cab 5.9, been steadily investing in repairs and now after 2 weeks another problem popped up. It will sit and idle fine then all of a sudden the iac valve is opening trying to get air into the intake, runs really rough then dies. This is happening for no apparent reason. My son works for a local dodge dealer and they have taken it in 4 times and cant figure it out. I have replaced cat, muffler, both 02 sensors, radiator, waterpump, thermostat, cap rotor wires and plugs. We have used the scope and the dealers reader and when it happens nothing changes at all, o2 readings, vacuum readings, timing. After it does it the third time i get a code for front o2 sensor high... but when it happens with scanner on it it shows normal on o2 sensors and stays there even after the check engine light comes on....according to all their machines it isnt happening. Any advice or help would be appreciated.

 

Rollover vave? What is fuel pressure doing when it dies? (that just seems far to obvious for the dealer not to check though.....)

 

Not sure we are still trying to figure it out, the fuel pressure is at 49 at idle and only drops to 45 even during the missing. We (son, myself and one of the dodge drivability techs he works with) ohmed out every wire in the engine control harness, relays, solenoids. We even swapped parts from both of their vehicles with mine to try and pin it down. still missing after 5 minutes of idling and every so often after that. The only thing left we believe is the ecu. going to pick up a used one if i can find one, sure dont want to spend $275 for a new one only to turn out to be something else. still open to anyones help at this point.... tired of burning up a tank full of gas everyday trying to figure it out....

 

Hey i Just went through that same sort of situation... My truck was doing the same sort of thing where it would start idle rough then die... so i called a few people and then my gf's brother...My GF's bro is a Wyo tech grad that works as a lead engineer for Chevron, and he told me the most Hokey Pokey way of reseting the computer but it worked. First I had to unhook both batt. terminals and touch them together for 30 sec, then leave them apart for 15 min so they are not touchin each other or any metal, then touch them together for another 30 sec, then hook them back up. I know it sounds weird but it worked my truck runs like a dream. IDK if it will work for you but there isnt any harm in givin it a try.

 

sounds like a poo poo map sensor to me.they dont always set a CEL when they get erratic.
I would throw the dice on that before the ecm.I missed the second half of your reply.Have you checked injector resitance?When they get hot sometimes the injector coil starts to fade,although that should be a steady miss.