Venom_1138

Rebuilt my carburetor last year, and after a few minor tweaking issues, I had it running properly. Took it out of storage this spring, and it's been running a tad high, like in the 1500-1600 RPM range. I haven't had too much time to fiddle with it just yet, but last night I put the front wheels up on a couple of ramps and changed out the oil for some 5w30 synthetic blend and added some BlueDevil Oil Stop Leak to it to try and revitalize the seals and see if I can keep the tired old 305 running for a couple more years until I can afford to upgrade the engine.

When I fired it up it was idling lower and I just figured it maybe had something to do with being on an incline and the way the fuel was sitting. However once it was back on level ground, it was idling at a very polite 800-900 RPM's. I took it for a short drive just to warm up the new oil and get it all circulated through the crankcase, and for a while it seemed like the sub 1000's was its chosen idle rate. I decided to see how it handled under load, so I went WOT and hit the highway (within the speed limits, don't worry!) Response was as good as ever, but after that, my idle rate was right back up to about 1500-1600 RPM's again. Parked the car, went in for dinner and called it a night, and figured I'd just have to check it out this weekend.

This morning, I decided to drive it to work today. I started it up from cold, and naturally it was running around 2000 RPM as the choke did its thing. However, once I tapped the gas, it dropped back down to that polite 800-900 RPM range again, nice and smooth. I had a quick errand to run before work, and as I approached a stop sign after driving about a mile or so, I noticed that the idle had jumped back up to the 1500+ area. After that, it never came back down anywhere below 1500. If I tapped the gas, after it revved up it would dip below 1500, but I don't think that was so much the RPM's dropping that low as just the needle bouncing a tad.

It would be one thing if it was just the consistent 1500+ idle rate, but when it's idling at a proper rate at times and then idling high with no way to bring it down, that's where I'm a little stumped. Obviously something is working right part of the time, but I don't know what's causing the idle rate to change. And I certainly don't get why the idle rate suddenly went down to proper levels after start up just because I changed the oil. I'm hoping one of the Quadrajet gurus around here can maybe point me in the right direction. Thanks!

sofakingdom

iTrader: (1)

Does this still have the OE carb on it?

What is the 8th character of the VIN?

Venom_1138

This is either the OE carb or if it was replaced, it was replaced with an identical model.

8th character of the VIN is 'G'.

sofakingdom

iTrader: (1)

OK, I don't think it matters, but just in case, good to know.

Sounds like the idle "kicker" solenoid on the side of the carb is a bit too enthusiastic.

Those have been installed for a variety of reasons over the years, in fact for completely different purposes in each case. Originally it was designed to hold the idle up when the AC turned on. Then later it was used as the "normal" curb idle; you set it to what you wanted the idle speed to be, say 700 or whatever, and then disconnected it and set the idle to like 400 or 450; it stayed energized 100% of the time the engine was running, and when you shut the car off, it dropped the idle down so low that it kept it from "running on" or "dieseling" whatever you want to call that. Then in the CC Q-Jets it was used as an emissions device on stick shift cars ONLY: when you pop your foot off the gas to shift a manual transmission car after accelerating in some intermediate gear, the mixture goes STOOOOPID rich for a second or 2 until the idle speed comes back down; so in those, the computer energizes the solenoid to keep letting enough air in to avoid that, then until the idle comes down to around 1400 or 1450, it drops it out.

Adjusting it is kinda fiddly. Best way I've found is: disconnect it; set the idle to around 700 with the screw; then energize it with an alligator clip lead or something to the batt or alt, and adjust the solenoid by screwing the plunger in or out, to about 1250 or 1300; then hook it back up. Different fuels have a YUUUUUUJJJJJJE effect on this, so expect to have to dink with it a bit. The correct effect should then be, you can hold the throttle lever up with your hand to give it some gas, and hold the RPMs at 2500 or so; let go of the throttle lever; the lever should come to rest on the solenoid, not the curb idle screw; the RPMs should come down, then after maybe a second or so, when the RPMs reach 1450 or so, the solenoid should drop out and let the throttle down the rest of the way. When you get it set right, it should be just barely noticeable when driving the car around, but almost undetectable. It also serves as an AC kicker but it doesn't have enough nads to push the throttle out by itself usually, it will only have the effect of holding the throttle up when letting off it with the AC on. You may find that it has too much "authority" on the AC when set correctly for emissions, which will necessitate backing it off a bit further. You'll just have to play with it until it works smoothly on all its functions.

Venom_1138

That was actually the source of one of my problems post-rebuild last year. It somehow became much more aggressively engaged and when I backed it down, my idle rate was back to normal. So when this started occurring after getting it out of storage the other week, my very first inclination was to back it down again, which I tried a few nights ago. However once I backed it down and restarted the car, my idle rate was just the same (1500+ area) and the solenoid wasn't even touching the throttle cable. I haven't touched it since, because that didn't have any effect on the problem. So it is a valid fix, but unfortunately I don't think it's having any effect this time around. If I have time tonight, I'll start it up and take a second look at the position on it when it's high idling and if possible, when it's in the normal idle range. Like I said, what's really got me scratching my head was that since I first started it this spring and until I changed the oil, it never went below that 1500+ range.

-I'm also not prepared to rule out the possibility of a gremlin living inside my engine bay.

sofakingdom

iTrader: (1)

Look at the choke linkage also. Maybe use a can of spray carb cleaner as your eyepiece.

Venom_1138

Didn't get a chance to look at it last night, but this morning it was back to the 1500+ range, and never dipped down to the sub 1000 area. When I pulled into work, it was actually idling right around 2000, which is usually where it kicks up to when the choke engages after first cold starting it. So based on the above post and the coinciding idle rates of a cold start and now, maybe it's the choke that's acting up and not fully disengaging and/or re-engaging itself?

sofakingdom

iTrader: (1)

It'll take less time to look at it than to post, wait, and read.

Venom_1138

Agreed, but I had just arrived at work and wasn't in a position where I would be able to pop the hood and look at it, so adding more information to the thread was the only thing I could do at that point.

I took it for a drive this morning, and it stayed firmly around 2000 RPMs. Later in the afternoon, I took it for a couple of quick errands and it started out around 2000, then settled down to around 1500. By the time I got home, it was back to idling just below 1000 RPMs. I finally had time to pop the hood and try and take a look, but since it was idling around the proper rate, I couldn't really determine what the high RPMs were being caused by. I let it cool down and started it again a few hours later, and it was still sitting in the sub 1000 range. A couple of times, it would actually start to dip lower and would sputter and die out. After a little poking and prodding, I noticed that tweaking the front air valve was affecting the RPM levels, and that there was a bit of loose play on it, meaning it could possibly be getting stuck in various positions, which could explain why my RPM levels are so consistently inconsistent.

I'm going to have to take a second crack at it tomorrow and see if there's any adjustment that can maybe take up the slack and tighten up the response on the front air valves, if at all possible.

naf

iTrader: (7)

the front choke should be loose. engine vacuum will keep it where it needs to be.

to rule out the idle bump solenoid, simply disconnect it for a while. a failed TPS may cause it to stay engaged when it otherwise should not.

Venom_1138

I've ruled out the idle solenoid, when I first looked at the carb during the high idle (before it started bouncing around) it was running at about 2000 RPM's and the solenoid wasn't even in contact with the throttle lever.

I'll have to catch it when it's acting up again, which is proving to be very random and making it a little difficult to nail down the root cause.

naf

iTrader: (7)

if you've confirmed that the high idle is caused by the curb idle being too high (not touching the curb idle set screw) there are two other possible causes

1) choke linkage keeping the fast idle cam engaged-either sticking linkage or a choke heater issue. test this by manually releasing the fast idle cam when the idle is held above the curb idle set screw

2) worn primary throttle bushings-when these wear the throttle can stick AND an intermittent vacuum leak can occur. test this by removing the return spring and, with the throttle slightly open, check for play in the throttle shaft front to rear. Any observable play is cause for a re-bush.

I assume you've ruled out the possibility of other, random vacuum leaks...in that when it is idling high the throttle is observed to NOT be in contact with the curb idle set screw.