check engine light comes on and cold blooded

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K5Blazerboy87

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hi guys im having issues with my 350 in my k5 i recently replaced my 02 sensor, my iac valve and connector cause i was told it was bad. its doing same thing before i took it in now its cold blooded in morning it always used to fire right up never had to give it gas now i have to and then after it warms up and i drive it for a bit my engine light pops on and idle goes weird just doesn't run right. took paper clip trick to it i popped code 42 4 flashes pause 2 flashes. HEI module ? it says i recently replaced my igntion control module so idk can anyone give me some info.
 

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hi guys im having issues with my 350 in my k5 i recently replaced my 02 sensor, my iac valve and connector cause i was told it was bad. its doing same thing before i took it in now its cold blooded in morning it always used to fire right up never had to give it gas now i have to and then after it warms up and i drive it for a bit my engine light pops on and idle goes weird just doesn't run right. took paper clip trick to it i popped code 42 4 flashes pause 2 flashes. HEI module ? it says i recently replaced my igntion control module so idk can anyone give me some info.
The coolant temp sensor controls fuel during closed loop cold starts. May want to look into that. Not the gauge sensor with 1 wire the one that tells the ECM coolant temps.
 

1987 GMC Jimmy

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You get a Code 42 when your EST bypass is disconnected. That's the one you unplug when you reset the base timing. Unless that's an old code, you need to go ahead and plug that back in and reset the computer by disconnecting the battery for thirty seconds. It's a single wire weatherpack connector on the driver's side of the firewall.
 
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K5Blazerboy87

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Coolant sensor is it one on the intake manifold on front by thermostat
 

K5Blazerboy87

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Cause I've replaced it to
 

K5Blazerboy87

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I had timing looked at too EST bypass is it a single green wire with grey connector
 

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I thought the wire you need to unplug to set timing is tan, iirc.
 

1987 GMC Jimmy

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The first single green wire with a gray connector that comes to mind is the connector for the temp gauge/light. The EST wire is tan with a black stripe. It looks just like this, but this picture is from a Camaro, and it's not on the passenger side like on that one. On a square, it should be right up against the firewall on the driver's side poking out of a loom just like this one IIRC.
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K5Blazerboy87

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I reset it it was plugged in made sure, made sure I reset computer then started it still cold blooded it stalls gotta give it gas then went to normal idle for 5 mins then the idle changed it seemed looked and light is back on and put pin in and popped up same code so Idk
 

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How did it run before you replaced the ignition module? Did it start messing up immediately or shortly after you replaced it? You double checked the bypass wire so, as far as I know, the only thing that could set that code off is a problem with the rest of the EST circuit (open or short to ground), the ignition control module, or the ECM. From what I've been able to garner, I wouldn't rush to suspect the ECM because you've got a working SES light and diagnostic circuit, which is a good sign. ECM failure is a strange thing sometimes, but I wouldn't think right off the bat that there was a problem there. I'm gonna attach the circuit/diagnostic description and troubleshooting chart from a GM TBI service manual for you.
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K5Blazerboy87

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Thank you appreciate help im pulling the engine next summer might rebuild put a rv cam stuff then might convert to carb Idk
 

K5Blazerboy87

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This time it was about 5 mins after engine warms up
 

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