I apologize in advance for any newb questions but this is the first car I've owned that is carb'ed and have zero experience with them and need advice, I have a 85 iroc and the issue I'm having just started recently upon starting especially cold starting the car seems to get stuck in high idle (1500-2000) and the check engine light will appear, however tapping the gas will bring the rpm's back down to normal (900) and the light will disappear after putting in gear and driving for a minute or so, can anyone tell me what I'm looking for?

 

Pull the codes when that happens, it will let you know what's throwing the code. After driving and when the engine is up to operating temperature do you still have the high idle problem?

 

*knocks on wood* no that's what makes it so odd to me, after tapping the throttle to bring it down and then driving within a mile the light disappears, car responds normally can turn on/off the car and It won't reappear until after the car sits for awhile (6 hours+) and/or there's a significant temp drop

 

On the passenger side of the carb is an adjustment screw to adjust the cold (fast) idle cam.

Look over there and study the linkage and notice how it works.. when the car is cold and shut off.

Adjust the screw to reduce or increase fast idle.
I assume this is a Qjet carb.

 

sounds like normal operational behavior to me, other than the CEL

 

Except For The Check Engine Light.

 

Listen to Naf...everything is fine.

What you are seeing is the high idle when the car is cold, the choke is open. Without this you'd need to hold the throttle down for a minute or so to get the engine warm enough to run. No issues in the summer but when the temps drop below 50 you need this feature. When you tap the gas that disengages the choke and the idle drops back to normal.

 

Check engine light is probably showing it running rich or lean. Mine did that when i swapped to the 355. Carb probably just needs a slight adjustment or potentially a rebuild.

 

My 355 (ZZ4 clone) didn't have that problem with a stock 305 q-jet (with upgraded rods & hanger). I just set everything to factory specs, it ran fine. Admittedly I'm at high altitude, but I did take it to Topeka one time and it didn't have problems there, either (ran low 13's in the 1/4 with 2500 stall and 3.23 gears).

Interestingly, I tried an experiment running a Holley 6210 (650 spreadbore double pumper) fooling the ECM with a throttle position sensor setup. It didn't really run any better (or worse), but in cruise I would occasionally get an SES light for a lean condition. After a couple of month I put the q-jet back on (never got a choke set up on the 6210, and it was getting cold again), and no more SES light.