Hesitation only when cold engine

[oldan]

1985 280 engine hesitates and sometimes backfires when throttle is depressed
run great when engine is up to temp. It is fuel injected. What do I need to look for?

[INSIDIOUS]

Idle air control.

[oldan]

Thanks for the reply. In referencing my workshop manual there are 2 different sets of instructions:
1)idle speed and CO mixture adjustments
2) idle speed and CO-content adjustment

which one should I tackle first?

[Frank Reiner]

Originally Posted by oldan

1985 280 engine hesitates and sometimes backfires when throttle is depressed. Runs great when engine is up to temp. It is fuel injected. What do I need to look for?

First, adjust the valves.

If it is in the US, it is a gray market car, and since it is a gray market car, some modifications and additions were made to make it acceptable to the EPA & whatever state it was first registered in. Describe those changes.

[hercules]

After valve adj. set mix adj. after warm ,only one place to set.
Idle speed should be auto.
Air flap may need to be adj. Should set level with housing just before air flap moves into
open space. Engine off. Small pin just behind air flap on top on housing,tap pin down,you go to far must take top housing off and tap back.

[hercules]

Would run fuel injector cleaner through also product that removes carbon on next tank.
Are spark plugs in good shape?
Is idle up to speed cold? etc....

[Skid Row Joe]

Originally Posted by oldan

1985 280 engine hesitates and sometimes backfires when throttle is depressed
run great when engine is up to temp. It is fuel injected. What do I need to look for?

I don’t know what to tell you about the "backfire," but I can tell you that my 6.2 liter, 455 hp. 2017 Fuel injected Corvette hesitates until warmed up.
My 6.2 liter Corvette is very "cammed," and it's always in a state of vibrating thunder and shaking at idle. This baby's wanting to always run at WOT! An amazing powerplant!

[oldan]

valves were adjusted and new spark plugs put in 1 yr ago--about 500 mi driven since then.
Worked fine until the last two times driven.

[hercules]

Now some useful info.
Old fuel poss.
Rust in fuel system caused by water, very poss.
A small piece of carbon lodged in the air gap of one or more spark plugs.