2.8 v6 Running terrible cold (Page 1/1)
nathanninjacube DEC 10, 02:51 PM
Hello, I bought my 86 fiero GT 2.8 auto about a month ago and it is super fun. However I am having an engine issue I can’t find.

Symptoms:

-Upon a cold start it fires as I turn the key but will instantly die when I let go unless I press the gas pedal. I must hold the gas pedal for 20 or so second or it will die.

-If I let go of the throttle too quick or put it into gear without pressing the gas (again only while cold) it will die.

-It idles really rough but smooths while warm. If carb cleaner is sprayed into the throttle while idling cold it will instantly die.

-Instead of a 2 second prime with key on the fuel pump is always on, unplugging relay turns off, switching relays has no effect. (Separate issue?)

What I have tried to diag:

-Cts was shorted, replaced and fixed any issues for when it was running warm, cold was unaffected.

-FPR has been replaced.

-Unplugging MAP while running makes it surge/die so it is at least doing something

-Unplugging IAC makes it surge as well. Air passage for IAC has been sprayed with carb cleaner.

-New spark plugs (had weird bosch ones in it w 2 ground points, have been replaced with stock acdelcos.

-Went over vaccum hoses, replaced suspect ones. Capped the EGR ones (egr was deleted before my purchase but solenoid and vacuum lines left)

Anybody got any other ideas?
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Thanks!
Nathan Shade
"The Cheese Wedge" Yellow 86 GT 2.8 auto with a blue roof.

[This message has been edited by nathanninjacube (edited 12-10-2025).]

fierofool DEC 10, 05:39 PM
A stuck oil pressure sensor can cause the fuel pump to continue running. Unplug it to see if the pump stops.

I had a similar startup problem with my 86. It ended up being the MAP sensor. I had to hold the accelerator until the engine warmed a bit. After the engine was at operating temp, it would start normally.
nathanninjacube DEC 10, 05:44 PM

quote
Originally posted by fierofool:

A stuck oil pressure sensor can cause the fuel pump to continue running. Unplug it to see if the pump stops.

I had a similar startup problem with my 86. It ended up being the MAP sensor. I had to hold the accelerator until the engine warmed a bit. After the engine was at operating temp, it would start normally.



Have tried to unplug the oil pressure sensor. The pump stayed running.

Ig it could be my map reading wrong? The engine gets WAY more unhappy with it unplugged. (way harder to start and runs worse)