I have an 84 Z28 with a 305 H.O. with a computer controlled carb and an automatic transmission. The car has a problem which nobody has been able to solve. When the car is cold, it runs fairly well. In some cases, particularly when it has not been driven for a few weeks, it runs excellent cold. When it starts to heat up, the problems begin. It idles fine but when in gear it begins to bog then surge repeatedly with the RPMs dropping to nearly 0 then surging back to normal. If I take my foot off the gas, it smooths out. If I keep my foot on the gas, it continues bogging and surging. "Flooring" the gas pedel has no effect when this is happening. These symptoms first started occurring under heavy load (accelerating hard) but the problem has gotten worse and now occurs under normal driving conditions. Today the car stalled out altogether when this happened.

The car has a new (remanufactured) computer controlled carb, new plugs, wires, cap, rotor, fuel pump and fuel filter. The problem existed before all of these replacements and it has gotten worse after. I've read that it could be a vacuum leak, a bad catalytic converter or even a dirty fuel tank "sock". I took it to a mechanic and they don't know what the problem is. They noticed the coolant temp sensor needs replacing but otherwise were as confused as I am. My problem is that I can't afford to keep throwing parts at this thing in the hopes that something will work. Any ideas? I see a lot of posts on this forum and elsewhere on the Internet and everyone seems to have a different idea. I'm looking for someone who has seen and solved this. Any thoughts, suggestions or ideas would be greatly appreciated.

 

Carbon clogged EGR valve.Clean it and replace gasket with a screened gasket.

 

have you verified correct choke operation and adjustment?

 

I will pick up a new EGR valve today. As for the choke, it came with the carb and at least seems to be working fine but if you have suggestions for verifying, I would appreciate it.

 

Wait. Its a computer controlled carb. And your coolant temp sensor is bad? THATS A BIG PROBLEM. Get an ac delco. A failed cts will cause bogging, rich condition


Also has the car sat for a long time, any time?

There could be rust in the tank.


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choke should snap shut tightly when you move the throttle shaft (tap the gas pedal) when FULLY cold.

As you crank the engine/when it first fires up the choke pulloff should immediately pull the choke open ~3/16". if not inspect the pulloff and vacuum line.

Choke should then begin slowly opening until it is straight up. It should be fully open within 2-5min depending on engine and climate. if it is slightly at an angle any time after this, its not adjusted correctly.

 

yes quick and easy way to rule this out before throwing parts at it is to put a jumper wire in between the 2 cavities on the cts harness. fools the ecm into thinking it is full hot.

if the car immediately responds, bad cts

 

My stock 1992 350 car is doing the same thing, its hard to start, When it does start, it idels like it has a big cam, then after a few minutes it clears it's self out and runs smooth, at idel while parked. for a few min. but the temp gage climes quickly to 260 super hot !! I check the coolent hose's and radiator with a lazer temp reader and all the hose's and radiator are showing normal temp 160-180 deg. when you drive the car it sputters and then clears it's self a little but as soon as you get in the gas, it just lays over like a wet noodle..or act's like it wants to die. I have changed the coolent temp sensor twice, and its still peging hot ! I also have the new injectors, the thin ones that are 22lb with an adj. regulater but i changed them a while back.