How steady should idle be?

[Dleslie212]

77 K10 with a Edelbrock 1405 carb, Edelbrock performer intake. As far as I know, heads are stock and I have no clue about cam. It has a 350 and a 700R4. It idles when in gear warm at about 700 RPM, but every ten seconds or so, it’ll drop about 100 RPM and then jump right back up. I also have an issue when driving - at about 3000 rpm, it will start surging down to 2500 and then back up to 3000, almost like I’m pumping the gas pedal. I have no idea if the two issues are related.

At first I thought it was a fuel delivery problem, but everything has been replaced now except for the carb, which still,looks almost brand new (no idea how old it is - it came with the truck)

My main question is about the idle - how steady should it be? Is it normal to have. A little drop in the rpm during idle, or should the needle on the tach stay pretty steady all the time?

[Ziegelsteinfaust]

Some engines no matter how tame do it.

I had a warn 350 in a Nova with a comp 265 cam, and bowtie heads that would lope every 45 seconds for what ever reason even at 800 rpm.

My friend had a Duntov 30-30 cam, and it would idle quite smooth at 900rpm once warm.

A manifold trick that helps a lot of vague issues is to grind away the plenum divider or use atleast a 1/2 inch spacer. This way both sides of the carb see cylinder pulses. Which can help from anything from hard starts to mpg. All depends on the engine.

[Dead Parrot]

Loosen the power piston caps enough to swivel out of the way, pull the pistons and spray a bunch of carb cleaner down the bores. If you park it hot, some of the gas will evaporate and over time the gum deposits build up. Sticky pistons could cause your cruise issues. A sticky float might be causing your idle surges. I don't have idle issues but have found that every couple of years it will develop flat spots on accelerations due to gum build up.