Hello all,

I will try to make this short but due to the complexity of the issue this may be long winded so ..please bare with me.
I own a 1991 c1500 5.7 tbi. only issues from the beginning was a rough start issue when the weather started getting chilly It would surge really bad and rev up and down .. stall etc until it was warmed up. It was and is not a daily driver so during winter months I didn't care if it ran right or not.. now I have used it all summer and have had no issues out of it.. the weather has turned chilly again. but now i need it badly ... here's where all hell breaks loose. I started simple. and started with some common things. Checking sensors etc.
I have replaced the EGR valve, Throttle position sensor, Map sensor, Coolant Temp sensor, Fuel pump relay, Distributer (entire dist.) and fully rebuilt the throttle body. as it is now... I can only get the truck to run for exactly 8 seconds. it starts fine and idles perfect for those 8 seconds then total loss as if you shut the ignition off. no sputtering .. no nothing. restarts perfect again. and same thing 8 seconds then Poof its off.

Now... heres the kicker ... I cannot get the truck to start if the MAP sensor vac line is connected. if I pull it off .. i ge the 8 second run time.. I swapped out the MAP sensor 4 times ... still nothing .. I even took my map sensor off and put it on another chevy and it works fine.... oh yeah .. if I start the truck and stay on the throttle .. it will stay running .. but as soon as I let off the throttle .. I get 8 more seconds and its gone again lol

I did the old paper clip trick and got 4 codes .. I got code. 12, 15, 33, and 34.. the last two are relating to the MAP sensor.. code 12 from what I gather doesn't exist.. and code 15 show to be - ECT/CTS (engine coolant temperature) sensor circuit high (low temperature). ..

I can only assume the codes 33 and 34 are due to the vac line being disconnected.

I am at a total loss here guys and girls .. but I need this truck running like YESTERDAY .. any thoughts would be great ... I have spent way too much money and time on this . so I leave it to those who may have experienced this is the past ..

 

Dang ... 146 views ....0 replys ... awesome lol

 

Up to 190 .. still nothin lol dang

 

Any help would be great ... still cant get it to work

 

Did you have any codes before your unplugged the MAP?

Unplug the battery, leave the map vacuum line alone .. does that set any codes?


"from the beginning was a rough start issue when the weather started getting chilly It would surge really bad and rev up and down .. stall etc until it was warmed up."


So what would happen if you gave it gas to open the throttle blades? Will it idle fine or choke and die? Will it warm up and be fine?

Is it the IAC? (idle air control valve)?

*sorry, I never had a TBI motor, so not sure how much of this applies.