CarburetorsCarb discussion and questions. Upgrading a Third Gen carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
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OK 87 LG4 with stock Qjet. Keeps kicking up to high idle whenever car is at a stop. I can sometimes goose the throttle and get it to settle down to normal idle. Normal and fast idle settings are right on at about 750-800rpm and 1200-1300rpm. It just will not stay at normal idle.
I've done a search and read several posts, but I'm pretty much an ignoramus when it comes to carbs. What my understanding is that this is likely a result of a bad choke heater or low voltage to the choke, or maybe if all else is ok the relay?
Carb experts am I on the right track?
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Mine was the same and found out it was a solenoid on the throttle bracket. I have not replaced it yet but as soon as I disconnected it, the idle is fine. I have a post in this section if you want to look at it.
The only way the solenoid in front of the throttle arm could cause this is if it is gummed up. It's not going to energize itself and raise the idle.
If your choke light isn't coming on, most likely it's the choke thermostat. Verify voltage at the choke with the engine running - disconnect the wire and check the voltage between the wire and ground. It should be 12 volts.
The only way the solenoid in front of the throttle arm could cause this is if it is gummed up. It's not going to energize itself and raise the idle.
There is a WAY OUT THERE chance that the solenoid could be intermittently engaged by the power steering low pressure switch, IF the car doesn't have A/C. The 87 LG4 has two connectors for the high pressure switch on the power steering at the box (at least every one I've seen). Non A/C cars used a low pressure-close switch to engage the kicker when the power steering pressure dropped. A/C cars used a low pressure-open switch to disengage the compressor clutch. Extremely unlikely but within the realm of possibility
LOL ok well its an A/C car and the power steering pressure switch was bad so I replaced it (was leaking )
Anyway, fired it up and while running and warm, I tested the voltage at the wire and the choke, grounded to the carb body. Got 13.9 volts, and of course the damn thing just sat there the whole time at low idle and burbled like a baby.
I guess I'll have to wait for it to not kick down and test it then to see if there is a different condition.
I was pretty sure it wasn't the solenoid, as it actually is not engaged when the car is at high idle, although I will double check next time it doesn't kick down.
hmm maybe I should just spray the crap out of it with carb cleaner?
Last edited by IROCmonkey; 03-10-2008 at 06:54 PM.
Perhaps you fixed it by pulling off the connector and putting it back on.
If the mechanism moves freely with the throttle held open slightly (check this with the engine off), then spraying it with carb cleaner isn't going to change anything.
Man, I'm having the same exact problems. Thing idles hight like that once the its warmed up, I gas it and it settles back down. I am hoping its something relativley simple. I've been trying to tackle all the little things since I bought the thing 4 weeks ago... its like a game of wackamole every weekend! I'll read around, but I am interested if you come up with the answer.
Perhaps you fixed it by pulling off the connector and putting it back on.
Well I didn't pull the connector off, it had a little split in it so I just stuck the probe into it and test the voltage.
Quote:
Originally Posted by five7kid
If the mechanism moves freely with the throttle held open slightly (check this with the engine off), then spraying it with carb cleaner isn't going to change anything.
Do you mean the choke pull off mechanism? Ok I will check it.
Do you mean the choke pull off mechanism? Ok I will check it.
No, I meant the butterfly and high idle cam mechanisms. The choke pull-off ("vacuum break" in GM-speak) is only meant to slightly open the butterfly when the engine first starts cold (and to hold the AV closed before the engine warms up - but that's a different topic entirely, just wanted to make sure I didn't leave the wrong impression about its function).
ok I'll look at the service diagrams in the sticky so I know exactly what you are talking about, I have a good idea...but like I said I'm a bit of an ignoramus when it comes to carbs
Another possibility is the primary throttle shaft bore is worn out. This causes the shaft to bind and stick when you let off the gas. Then you have to goose the throttle a few time to get it to unbind. They sell kits to repair this. Like this one: http://www.jetchip.com/products.asp?pid=23044
I've had this problem before but I live close to some high volume wrecking yards and can pick up decent carbs for $30 so I've never shelled out the money for the kit.
Well sitting in traffic this morning it did it again, will not come down off of high idle step when I stop, wants to sit at 1000-1200 rpm. When I can get it to kick down, it sits right where its supposed to be at 800ish.
I need to check the fast idle cam (see if its sticky, or maybe binding up on the aftermarket air cleaner) like five7 suggested still, and I need to check the resistance on the thermostat (I have good voltage, but I didnt check resistance)
How do I check the shaft bore, is that just the shaft the butterfly swings on?
When the problem arises, pull it into a parking lot and leave it running with the high idle and get out and see what's stopping the throttle from rotating back down. If the idle just runs away into high rpms when you put it in nuetral then 'd think its not related to any choke or idle mechanisms. Just shut it down without touching the gas. Then go look for what is not letting it rotate. If you can simply turn the shaft down by hand then somethings sticking. maybe the throttle cable itself.
Last edited by chesterfield; 03-11-2008 at 11:21 AM.
No the idle never runs away. It just won't kick back down into low idle.
The only reason this aggravates me is the wasted gas and that if I shut it off at more than 1000rpm it diesels and that drives me bananas. I like my stuff to run at least sorta right
I just started driving this Camaro this week. In the last few days I've already discovered several things that need attention, but over all its a pretty decent running car. Now if the clutch was a little less stiff.....but thats a whole nother thread
OK had the chance to check resistance on the choke thermostat. From connector to ground I was getting between 18 and 27 ohms. From what I have read this means the thermostat is on its way out or toast.
Nothing is binding up on the air cleaner. I tried to move the fast idle cam and the primary throttle blade but they didnt move much, felt like the choke was holding it open
Checked all this with the car off, after it had sat for about 3 hours cooling off.
rather than trying pump money and serious time into figuring out what is wrong with my carb, can I replace the whole thing with a rebuilt carb and sell my old one? I think my existing one needs to be rebuilt, but I am a slotard with carb's. I would rather just put the same one on there that is effectivley brand new unless there is some overwhelming reason to get something else for my stock 305 mouse mobile? Its going to get warm up here on the east coast before we know it, and I can't keep dicking around every weekend with this thing.
I'm having what has to be the exact same problem as listed above with regards to the idle. I would like to think its something simple, but its most likely comprehensive given how long this thing sat.
A rebuilt ccc-qjet from a parts store will run around $300. I can buy used q-jets all day for $30 'round where I live, so not sure what your old one would be worth.
There are probably a few good running carbs available from members here if you post in the 'wanted' section. I know of two members that recently offered up a known good ccc-qjet for sale. Don't know if they still have them or not.
DO NOT be tempted to put some other kind of carb on there with the hope that something shiny may make it perform better. You'll wind up having to muck with a new dist, torque converter lock and end up with a mess that doesn't run any better than a properly functioning computer controlled system.
If the choke is sticking will it keep the fast idle stepper from moving?
If I disable the choke, and my idle problem goes away, then problem solved right?
YES and NO
You can temporarily disable the choke, may be with a zip tie or something to hold it open, and see how it does. You will need the choke for cold weather startups. Fixing it is best. If the choke thermostat is bad, should be pretty easy to find another. The electric choke for q-jets is pretty much the same from one to the next. The last few used q-jets I bought cost me $30 each. Each came with an electric choke assembly.
My "Berlinetta #2" had a newly rebuilt carb on it when I got it. Whoever was working on this car to get it through California smog test was only marginally competent (I didn't actually meet the previous owner, as it was a 3rd party sale). It had been started and warmed up before I first drove it, and ran decent. But, the next morning when I went to start it, it took forever and then it wouldn't idle until warmed up, and then it idled too high. Turns out this "mechanic" had tied open the choke rather than take a few minutes to adjust it properly, and set the "normal" idle too high to compensate for it. Since I was away from home when I picked up this car (flew out to get it), I had to go buy some tools and start doing these adjustments. Everything worked fine after getting things set to spec, including when I went through the Colorado emissions testing upon getting home (passed easily).
Since this car is getting an LS1, the carb is now available. Let me know if you're interested (I'll beat that $300 price). You may be able to bolt it on and go, but I will only say that it will operate properly after any necessary adjustments are made.
These carbs are really good pieces when they are given the chance to do what they are supposed to do. Being inoperative for long periods of time when gas can evaporate and gum things up (improper storage) is probably the worst thing you can do to them. Right after that is doing stupid things like monkeying with adjustments or mechanisms without knowing what it's supposed to do.
I agree with ya on that five7, I don't believe in "ghetto fabrication" or "******* engineering" except as temporary measure until something can be fixed properly.
I can get a replacement choke element for about $30 locally. I just want to troubleshoot the problem and be sure.
Sad thing is since I live in Florida, I don't even think there is such a thing as cold weather start.
I'm going to dink with it this weekend and see if I can't get somewhere.
It can't be too out of whack adjustment wise, as the motor runs surprisingly smooth and strong for a 20 year old LG4 but it does drive very different from my TPI IROC.
lol forgot that 7 letter word that begins with r was a no no
Last edited by IROCmonkey; 03-13-2008 at 03:04 PM.
The thought of bolting anything on other than the exact replacement would never cross my mind. I also wouldn't swap anything on without it being completely 100% either rebuilt or NOS. I just think my old carb needs the rebuild here shortly, although I don't think its anything completely out of wack. I don't even know where to start to diagnose the problem unfortunatley.
If you guys had my carb, and problem, what would be the obvious things you would check to eliminate them as problems first?
have you tried the trouble shooting steps I've already done and the ones suggested by five7 and chesterfield?
to sum it up:
Ive checked the voltage at the choke thermostat connection (good)
Ive checked the resistance at the choke thermostat connection (bad)
I need to temporarily disable the choke and make sure the fast idle cam and the throttle blade assemblies are moving freely. Once I do that little bit I fell fairly sure I'll know the solution to my idle problem. If disabling the choke doesn't work, then I'll move on in troubleshooting, if it does I'll get a new choke thermostat.
I don't think anything is gummed up or springs not positioning things where they are supposed to be.
I am going to change the two vaccum lines on the air cleaner box as they were the only ones I did not replace, but I think they are fine and are not part of the problem.
I am curious, the choke thermostat is actually an actuator correct? When the car is fully wamed up, the choke should be completely closed. I read the manual once today, but I'm kind of on my own, so I'm still not 100% sure who the whole thing works yet. I don't know anyone who can show me this stuff.
It would almost seem easier for me to see what was actually happening if I have the air filter off, but I know thats a no no correct?
Also the gasket around the top of the carb is shot (the one in between the air cleaner and carb). I assume I can pick that up as a single item at autozone tomorrow?
Also, tomorrow I am going to replace the 02 sensor to eliminate that as a problem.
The choke thermostat is not an actuator. It is a combination bi-metallic spring (aka - "thermostat"), and heat coil. The wire going to it heats it up so it releases the choke. That's all the electricity going to it does.
Before you start it cold, open the throttle all the way and the choke should close nearly completely. Start it up and you should see the choke blade open slightly, this is the choke pull off holding the choke open a little with engine vacuum. Watch it run for a few minutes and you will see the choke blade continue to slowly open as the coil is heated by the 12 V. It should be completely open (90 degrees up) within a few minutes. Tap the throttle at this point and the motor should come off high idle (fast idle cam is allowed to drop once choke is off) and idle is controlled by curb idle adjustment.
looked at the carb today, nothing seems to be binding up. Its all very loose though.
Took it for a drive after I got the driveshaft back in (I swear it was about 2 secs from pole vaulting). Idle wont come down. So I pull it in the garage, whip the the hood up and the cleaner off. Look at the carb..looks fine..then I tapped on the throttle linkage, pushed it forward and the idle kicks down.
So I tweaked the linkage a little and bent the end of the throttle spring to give it a little more tension. Seemed a little better on the way home.
Looks like a lot of the moving parts are just loose and wore out. Will see how it drives in "real world" conditions come tomorrow.
Not to hijack your thread... but! I changed the 02 senor out, and it seems to idle a million times better once warm. Its sitting at 1500 rpm's, but I'm not sure exactly where it needs to be.
I think I will also check the stuff you did with regards to the general tension on everything.
I did some other stuff too, but I'll spare the details.
check your under hood emissions sticker...if its still there. low idle should be like 600 or 750 with it in gear (i think). and high idle should be about 1200. using stock tach for those readings is largely a guesstimate (amazingly, the stock unit in my LG4 is pretty close, first time I've ever seen a 3rdgen that was), does the idle "sound" high?
yes it does sound high. I hate the mess with any screw or adjustments unless I am 100% sure I'm doing the right thing. I think there are 4 adjusment screws? Is there a main one that I should be looking at. Or the idle air control (which I would have no idea where it is). I think the choke is fine. I've been reading my manual, but I am still a retard.
I need to make friends with some people who work on cars.
IROCmonkey, you might simply have a linkage problem for what connects to the carb, and nothing wrong with the carb itself.
spiderhole, it would be worth your time to go through the E4ME sticky in the top section of this forum. It has the factory manual information. Some of it won't apply to you (such as the idle speed control), but it should help you understand what different things do and how they should be set.
well I am pretty sure now it is just a case of it being loose and worn. driving this morning it idled a little better at stops, and I was able to get the idle to kick down more often. It still doesnt want to kick down to curb idle on its own though. I'm thinking maybe if I replaced the spring on the throttle it might help. Also, I think there may be some merit to what chesterfield suggested about the shaft bore being worn out, all of the parts on the exterior of the carb are loose enough to rattle a bit.
Overall tho I am pleasently surprised at how smoothly the car runs, the engine is smooth all the way through the power band and never bogs or stumbles. Quite surprising considering the amount of neglect I've encountered elsewhere in the car. It does run a little rich at times, but that is not surprising and its not a bad problem.
I have the complete GM shop manual (the thick one), but its not all sinking in yet. Like I said, I am kind of on my own, a true novice. There just seems to be several adjustment points. I guess I have to start from the top. But, It doesn't seem that far off. The carb is by far the trickiest thing I've run into yet with the car. Everything else has been pretty straight forward. Carbs are confusing to me.
Last edited by spiderhole; 03-17-2008 at 08:33 PM.
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