Service engine light flickering ECM

[StepinNJ]

Went to drive my 1990 5.7 the other day and it kept stalling at low idle. Noticed the engine light flickering fast but not staying on. Took it to a mechanic who says computers from back then (truck is a 90) go crazy in extreme cold weather (It was 13 degrees). Is this true? Once the truck warmed up it stopped stalling but the light keeps flickering. He says I might need a new computer @ $225.00.
If so can I change it myself? Found them on line at rock auto.com for $86.00 with a core return.

[ChevyTech]

I am in Minnesota where 13 degrees is not considered very cold during the winter. At 13 below zero then we say it is cold out. I have never heard of what the mechanic told you.

My guess is there is a marginal connection somewhere.

The ignition switch is a common weak spot on these trucks. They can make and break connection. You could try wiggling the connection at the ignition switch on the lower end of the steering column.

Another problem spot is poor connections at the stud & nuts at the junction block under the hood on the passenger side of the firewall.

The ECM is not a common failure part.

[StepinNJ]

He went over all the obvious connection problems. He told me to wait until it gets into the 40's this week and see if the light goes out. Truck only has 82,000 miles on it and it's well kept mechanically.