Join Date: Mar 1999
Location: College Park, MD USA
I recently posted on here about starting trouble with my 86 IROC 305. You guys were right, it was the choke pull-off on the carb, and I appreciate your help. I recently had my Quadrajet rebuilt and they put on a new Choke Pulloff and a TPS, which I'm assuming means throttle position sensor. The car starts beautifully and warms up fine.
Unfortunately, another problem has emerged. The engine runs fine while warming up, but once it is warmed up, the idle "fluctuates" around 1200rpm, I mean the needle sort of bounces and the engine won't stay at a steady idle speed. The fluctuation seems to have gotten less the more I drive it, but if I let the car idle, the idle speed will slowly drop over the course of a minute or two until the engine sputters or stalls altogether.
Strangely enough, this never occurs above 2000rpm, and I can usually bring the engine back to life with a press of the throttle, but whenever it idles the RPMs slowly fall.
I don't know what could be causing it. I remember I did snap part of a small plastic hose that seems to go nowhere anyway, but I tried putting my finger over it and it didn't change the engine behavior, nor did I feel any suction or pressure. I tried spraying carb cleaner around some suspect vacuum lines, but no response. Actually I really can't tell which lines are vacuum lines because they have that ridiculous Air Injection system on the 86 H motor for pollution control. Besides, a vacuum leak would speed up the engine idle, wouldn't it???
I'm also thinking that maybe the previous owner jury-rigged the car to work with a broken carburetor. If he did, then maybe the rebuilt carb or the new TPS or CPO are sending signals the engine was J-rigged not to handle and this is causing a problem.
It may have also been a rebuild mistake. The shop I took the carb to is usually reliable, but I wouldn't know how to diagnose a carb problem/error. I can usually come pretty close on natural failures, I can't diagnose my or others's mistakes.
Does this symptom sound indicative of anything in particular? Any suggestions on what to try?
Any help would be greatly appreciated.