Fast Idle Faster!

DWCaprice2017

Not-quite-so-new-guy
Oct 25, 2019
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Hi, All!
I have an ‘84 Caprice, 305, with an electronic Quadrajet. Before starting the cold engine, I pump the pedal three times, turn the key, it starts on high idle that’s slightly rough, then after a few minutes on the fast idle, it goes to a slightly faster idle and smooths out!
What the heck is going on?
I have a feeling this problem is why, after tapping the pedal, the slow idle is a bit rough.
 
Vacuum leak? Check vacuum hose connections and hoses for cracks/splits. Tedious process. Also check the carb hold down bolts for tightness. Not uncommon for them to loosen over time. Also, the choke pull off working properly? There's a number of things to check, but long distance checking with one sentence to diagnose over the interwebs is a bit tough.

Has the carb ever been fiddled with? If the adjustments are tweaked, you could have some issues there as well.
 
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after a while when it smooths out thats probably when the computer kicks in and richens it sounds like it;s running lean before the computer kicks as 69hurstolds said check for vacuum leaks make sure all vacuum lines are tight fitting vacuum cheak each line they might look ok but won;t hold vacuum check choke too of course this is just what i would check first . don;t mess with the carb adjustments unless you know what you are doing
 
May be way off base on this but after checking for a vacuum leak as mentioned above check the choke pull off. May be keeping the choke closed causing the rough idle during warm up. As the element warms up the choke is opening allowing the engine to run smoother.
 
Thank you all for the great advice!
Some of those vacuum hose are a #@&%-ing challenging to get at!
Here's the story: About a year and a half ago, the car was running roughly, stalling. I had the carb re-built at a shop--the guy took it off the car. Upon getting it back, four days later it was running horribly, I took it back, he rebuilt it again, he found a particle had gotten stuck--maybe under the accelerator pump, I'm not sure. The car ran fine for some months, then it started idling roughly again. I took it back to the shop he re-built it again, saying that there was dirt in it--even with the proper filter in it. I suppose it's possible since I don't keep a lot of gas in the tank that some dirt got sucked in. He told me he thought the distributor might have a problem--without specifically checking it. When I took it home from the shop, it wasn't running quite right, I decided I had enough of this guy. Looking back now, I think the guy knew how to rebuild carbs but wasn't specifically trained with electronic Quads. The reason I think this is that he set the idle speed too low--he didn't have anyone to put it in drive and make an adjustment under load. No, I've not touched any settings on it. On the first re-build, the carb re-build guy replaced some electronic component in the carb, I don't recall what that was.

Since I have no confidence in the car currently, I've been taking the bus to work--actually saving me a lot of gas money! I start the car a few times a week and I move it once a week for street cleaning--once on the road, it sounds great, but at idle it's a bit rough, and the last time I drove it, there was a second of dieseling.
 
That carb guy is an idiot. You cannot "tune" a CCC quadrajet off the car. Just rebuilding it doesn't "fix" it. It must be running with all the ECM crap working. You can get it "bench set" which means close enough to get it running, but you need some time with it, some specialized tooling, and an analog dwell meter and voltmeter (for TPS, throttle position sensor) to get things set properly. TOO many idiots out there don't understand CCC quadrajets and will basically ruin your day. You can't set them by "ear" either. The M/C solenoid needs to be set precisely as well as the TPS. Then you have idle air bleed valve settings and idle mix screws to contend with as well. Got to get them all singing the same song.

Are you getting any codes thrown? It's very possible the ECM or like he said, distributor issue causing you pain. I don't know. It just sounds to me you need to get some further diagnostics done on the car to pinpoint the issue.
 
google how to get codes from a ccc carb computer .then after you wright down the codes disconect the battery for a couple of minutes that will clear the codes then start it up and drive it and see what codes came back ..first vacuum lines you have to rule them out do you here clicking from the carb when running ? that will tell you if the computer is working also google how to test the map sensor with a volt meter it won;t run right if thats not working
 
another way is to put in a non ccc carb and distrubtor that will do away with the computer then anyone can work on it
 
There are lots of resources here on how to rebuild and adjust eQjets https://gbodyforum.com/threads/gm-ccc-service-videos.76761/. Some of the tools you can make yourself. Some tools you will need to purchase such as an old analog dwell meter and a old scanner like a alltest brainmaster. You also will need a flexible screwdriver extension for adjusting the idle stops. One thing I quickly learned about vintage computer management systems is that you need to become your own expert at repairing them. Its not hard, but it takes time to learn.

Keep in mind that when the engine is cold, the ccc system is in open loop where it ignores the of sensor and operates off of default settings. Once the engine warms the system enters closed loop and begins to respond to of sensor reads. A very common problem with these systems are tampering and bizarre Jerry rigging by clueless former owners. Most car guys were not used to computers back in the 80s.
 
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