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Discussion Starter #1
hey new to this site but i have a 90 d150 with a 318 TBI. the truck has been dying on me every other day --i'll just be driving and it will sputter and die. it also idles very rough. i put the scanner on it and it gave me several codes. one being the map sensor. i changed the map sensor then it said tps.changed that . now it says pick up coil. i also changed that and it still runs the same. alot of people are telling me it sounds like the computer is going bad. what do you all think. any suggestions would be greatly appreciated because i dont know what else to do.
 

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It could be. But there are a few other things to check before going to that expense. Have you checked your fuel pressure? When was last time the fuel filter was changed? Have you checked your spark plug wires? If one or two are bad and grounding out the spark it will run like that. Check plugs?
 

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AirFuelEddie
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What were the codes that were found when you accessed the data stream? Did you engage the key on engine off 3 cycle test or was this found through a scan tool? Computers, aka ECM's or PCM's dont ' start to go bad' they either work or they dont.
 

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True that a ECM or PCM either works or it doesn't. However there have been known cases of EEprom corrosion that can mimic these symptoms. The corrosion is normally caused by a heater core that has a small enough leak that the water in the coolant system (not the coolant) vaporizing. Chrysler did not use Gold on the contacts of the eeproms. So this moisture can get to the ecm. Also a loose connection to the ecm can be a cause of this erratic behavior.
 

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Discussion Starter #5
i changed the fuel filter when these symptoms started to occur--the plugs are good as well as the wires. i did the 3 cycle ignition thing, it brought up code 35 which states" open or shorted circuit in the idle contact switch" cant find anything in my haynes book about an idle contact switch nor do i know where it is. the map sensor,tps and pick up coil where picked up from the scanner. also found out the transmission shop that rebuilt my tranny a few years back took out the vehicle speed sensor and just put back the speedometer cable. according to haynes the "vss" tells the computer how much fuel to dump in the throttle body and other things. could that have been part of the problem?
 

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Right off the top of my head the "idle contact switch" isn't ringing a bell. But I am about half out of it right now. The IAC is A computer-controlled air bypass valve located in the throttle body. It helps control idle speeds by allowing air to bypass the throttle plates as to increase the idle speed. Clean that out or replace it and most likely the problem will go away. Normally they can be cleaned with a can of gumout or something and will be fine . If it is the IAC and is sticking there is the problem. When cleaning do not use brake cleaner as it can damage the plastic of the connector and will swell the little gasket of it. So be sure to use a good carb cleaner. Also try your best to keep the connector clean and don't get anything on it like the carb cleaner.

 

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AirFuelEddie
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I would test two things here. I would want to know what my fuel pressure/volume are. I would also test the Coolant temp sensor as they 'age' they will collect corrosion around the thermistor element, this sensor is the NUMBER one component that determines the fuel ratio especially when starting after sitting all night. The other thing that leads me to believe that it's a possible fuel problem is the fact that you didnt state when this particular problem occurs. It's difficult to help in diagnosing a problem when we dont have enough data. Does this happen ALL the time or intermittently? Does it happen after a cold start or when idling at a stoplight? It just dies after driving is helpful but when exactly does this happen? After the engine is warmed up?
 

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Eddie is most likely on to something. After thinking about it , it does sound like a fuel starvation problem or an overload flooding it. You haven't said if it is flooding or not.
 

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4 Wheel Power Disc Brakes
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TBI doesn't use an IAC which bypasses the throttle.
TBI does use an ISC (Idle Speed Control) motor. This opens the throttle to increase airflow.
 

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My 88 W100 with the 318 was having an overload problem and I just got it fixed today. There were 3 different issues that were fixed. First off some of the vacum lines going into the Throttle Body were incorrectly hooked up. Second the Throttle Body Temperature Sensor was bad or should I say falling apart (I might have accidently done this trying to get some of the vacum lines off). Third the Coolant Temperature Sensor was reporting the engine being colder then it actually was. After these 3 items were fixed I have not had an overload problem and the truck is running great. Not sure if this will help you, but I thought I would let you know.
 

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check basics first, air filter, plugs, wires, fuel filter, etc. next remove throttle body get some carb cleaner and a tooth brush and clean the throttle body throughly. put it all back together. clear all inactive fault codes. if it still does the same, you'll have to diag logged codes
 
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