(I've also posted this over in General on a ongoing thread I have there, but being carb-related I figured it could also go here...)

Well I checked the solenoid plunger travel last night- it's within spec, so I'm beginning to think I'm going to have to either readjust the idle bleed valve and/or break open the seals on the idle mixture screws and reset those.
Just how difficult is it to remove the plugs on those idle mixture screws? The manual shows one way of doing it (cutting slots in the throttle body under the plugs then chipping out the resulting tab and plug), but I also noticed Thexton has a tool to remove the plugs. Has anyone removed these plugs before (with either method), and if so- just how hard is it to do?




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Original owner - '84 T/A w/stock 305HO 5-speed

 

I used the method in the shop manual. It is the same method recommended by High Performance Pontiac Mag and the same method in the Haynes Rochester book. If you follow the steps and be patient, it is easy. A hack saw will take you some time. I used a dremmel tool w/cut off disc and had both caps off in under 5 minutes. The throttle base is aluminum, so it cuts easily. Just don't cut too much or you might cut into an internal passage way. Then you would be f*****. When adjusting the screws, be careful not to overtighten them at any time or you WILL mess up the neddle tip.

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1983 T/A LG4 w/T-tops
Rebuilt/Modified E Q-jet
Custom Dual Ram-Air
Self painted cherry red w/ restored black/grey interior
Welded Comp Eng SFC
Tokico Struts/Shocks
Hotchkis LCAs and Panhard Bar
Energy Suspension bushings all around

 

So as long as I stay within the marks on the throttle body when I cut the slots I should be ok then? I've got a Dremmil too but it's a battery-operated one. Not sure if it'll have the power to run a cutoff disk or not (or at least long enough to be able to do anything) but I'll try that first, then use the hacksaw blade if I have to.

Thanks!

 

If your car is near stock, chances are you won't have to fiddle with the mixture screws. Adjusting the IAB alone should be plenty to get you idling right. if you can't get it right by just messing with the IAB, then you can worry about the rest.
...ed

 

Just to add use a dwell meter on the 6 cyl. scale.

-Auggie-

 

Well I don't have to reset the idle mixture screws if my idle air bleed valve is not 'lettered'- if it is, then according to the manual I HAVE to use the idle mixture screws. I haven't removed the cover to the IAB yet so I don't know which type I have....

 

When you're ready to fine-tune the idle mixture, be sure to go to your ALDC and put the ECM in Diagnostic mode. This will hold the solenoid cycling and the timing steady.

Get both sides evened out and then adjust the air bleed. If all goes well, you should be able to remove the shorting wire in your ALDC and the idle will not change. That means your ECM is satisfied with what it sees. That's what you want.

 

Since right now my idle dwell is < 10 degrees fixed, I want to start adjusting the air bleed until it starts varying - correct? And if that fails then that's when I'll have to readjust the idle mixture screws and try again?

My main concern here is not so much my dwell (or lack thereof) but the fact that I'm apparently running in open loop mode when I should be in closed loop mode. If I can adjust whatever needs to be adjusted to the point where I can get the dwell to vary again I'll feel that I'm 99% there.

 

David you must remember that the 02 sensor will cool off (below 600*F) at idle and your dwell will go to a fixed pos. When i check my dwell at eng. idle (6 cyl scale) i will see the needle stop verying. The Ser. Man. says to hold the idle at 2500 rpm to restart the 02 sensor.

-Auggie-

 

Auggie- ok, so I should never expect the idle dwell to start varying- but I DO want it above 10 degrees tho, right? I think that's the source of my idle problem to begin with.

 

Ok I tried adjusting the idle bleed- no joy there, either. Had absolutely NO affect on the solenoid dwell. BTW I had the 'unlettered' valve so I didn't have to pop off the mixture screw caps- at least not yet...

Oddly enough, I tried it both in ALDC mode and without and it made no difference. Odder still, while watching the dwell, I noticed that for about 5 seconds the dwell will change slightly- that is, from 0 degrees dwell it'll rise to about 5 degrees for about 2-3 seconds then drop back to 0 again. Then it would stay at 0 for about 10-15 seconds then repeat the cycle. Haven't a clue as to what's going on unless the ECM is doing a check to see if it can lower the richness and for some reason finding that it isn't helping, dropping the dwell back to 0 again.

Unless someone's got a idea as to what's going on here I'll go ahead and pop off the idle mixture screw caps tomorrow and try readjusting the mixture. What baffles me is how this thing can get so out of adjustment just by opening and closing the top part of the carb where you have to resort to resetting the mixture screws....



[This message has been edited by David Trimble (edited November 17, 2000).]

 

David, i am not sure about this but a dwell reading below 20* would be a rich command or a lean eng. When the eng. is at operating temp close the choke about 3/4 of the way and see if your dwell meter neeedle will move up the scale. If it does that will confirm a lean cond. Plug all vacuum ports at the carb and see what happens.

-Auggie-

 

Oh yes, I've already tried to choke the engine and it'll run up to but not beyond 50 degrees. I've got the EGR vacuum disconnected at the carb right now so that's not the culprit, but I'll reconnect it and disconnect everything else (I assume I won't break or ruin something in doing so?) and try it again. Will let you know what I find out tomorrow morning.

Thanks!

 

Well I went ahead and pulled all the vaccum lines, connected the dwellmeter to the mixture solenoid. Then I started the car and one by one reconnected all the vaccum lines. I started out around 20* of dwell- certainly much better than what I had been experiencing before, so that in itself confirms that the problem is actually a vaccum leak somewhere. Anyway I started reconnecting the lines one at a time then waiting a few minutes for the ECM to compensate to see what the dwell would do. Now I experienced a change in dwell (dropped to about 10*) when I reconnected the line going to the PCV, which I decided was normal as it certainly didn't slam the dwellmeter to 0*. However when I reconnected the line which serviced the air management system and the heat riser valve it dropped to 0*. Disconnecting that line again I tried readjusting the idle air bleed valve and it did react- I got it readjusted back up to 30* and the idle is now pretty stable (certainly much better than it was before). Of course, reconnecting the guilty line would slam the dwell back to 0* again.

So I've got a problem with either the line for the heat riser valve, or the line for the valve controls to the air management system, or the air management system itself. Narrowing which it is is the next step, and I have a feeling it's going to be the air management system as I did check out the heat riser valve and lines before and they're pretty tight.


[This message has been edited by David Trimble (edited November 18, 2000).]

 

David don't discount the heat riser because it is a vacuum operated heat riser.

-Auggie-

 

True, but I tested the riser before a few weeks ago when I was tracking down the idle problem (this has been going on about a month and a half now) and it held vaccuum. I did find tho that my TVS (thermal vacuum switch) that controlled the heat riser had gone bad and was staying open all the time, so I had replaced it. Needless to say it didn't affect the idle problem, tho.

What I'll do tho is reconnect the hose at the carb controlling the AIR and heat riser, then disconnect first the heat riser at the TVS, then reconnect it and disconnect the hoses to the AIR valves and see which causes the drop in dwell. I'll probably have to wait 'till Thanksgiving before I can get around to doing that tho but I'll let you know what I find out, of course.

Thanks!

 

I am also having a problem with my car running full rich and I got a dwell meter to test out the MC solenoid. It reads zero but when I first put it on it jumps up then I never get a reading again. Can you tell me how you hook the dwell up to test the MC solenoid to make sure that I am doing it right. I already failed emission testing once and I really do not want to go to a deal to get it to pass.

 

John it sounds like you have the exact same problem as I do. You're supposed to connect the dwell to the unconnected green connector that's over near the fan motor on the left side of the engine compartment (facing the engine). At least that's how it is for '84s. You can't miss it, it's the only connector there. But your dwell is exactly like mine- in fact I was running so rich I thought my dwellmeter was dead so I tried it with a friend's and got the same reading.

First before tearing into the carb, do what Auggie suggests and plug your vacuum ports. That's how I found my problem- so far I haven't had a chance to narrow it down to either the AIR or the riser (hopefully I can have time to do that tomorrow) but one of them has a vacuum leak.
That was my big problem- since I had recently rebuilt the carb I blamed the problem on the carb when it really wasn't. So check CAREFULLY for a vacuum leak and save yourself the headache I went thru.

 

I will try that. I also just rebuilt my carb lately. I already replaced a lot of vacuum lines this summer since they where never done by the looks of things. I did a vacuum check on carb and its about 30 and if I give it gas hard it drops to below 10 but if I increase it slowly it does not dip down. I will just get some plugs I guess and plug up everything and then go from there. Thanks. I will look for the connector and see if I can find it. I will let you know if I have problems.

Thanks and good luck with your leak.

 

Yea I just checked yesterday and apparently the problem I'm having is in the air management for the AIR system. Unfortunately I didn't have my manual with me so I wasn't able to run the tests for the AIR, but I suspect one of the diverter valves has developed a vacuum leak. Guess I'll find that out this weekend when I run the diagnostic ....

 

You better hope you do not have to replace that valve system. I checked into it since for some reason mine does not work right any more. (dealer cost $360 I believe that was the quote I got) I know it is the computer causing it thought. For some reason it is stuck on bypass so no air is getting put into the exhaust. I went to the junkyard and picked one up but still had no luck. I have pretty good vacuum to them so I know its not that unless it needs to be more. I hate the manual I have now but I have on order. The factory strip down manual with all the specs. I hope that is better than Haynes manual which does not even show much for 84. I looked for the connector but could not find it. Do you have an electric fan or clutch fan? mine is clutch and I do not see any kind of connector. Should it be in the open or is it connected to something you can reference? Thanks

 

John25, you sound like you have a classic case of bad / maladjuusted TPS. Unexplainable constant enrichment mode and your AIR is always venting to the atmosphere by order of the computer. Both will happen with a bad TPS. I'll bet you also have a slight stumble coming off idle when you're warmed up too.
...ed

 

I hope it isn't, either. I heard that valve wasn't cheap.

The shop manual's not bad but it takes some getting used to- especially the diagnostic charts. It'll definately be a step up from a manual that tries to cover several years.

Connector- sorry, when I said fan, I had meant the heater-A/C fan in the firewall, not the cooling fan. Pop the hood and look at the engine- over to the passenger side near the firewall look for where the heater-A/C blower motor sticks out of the firewall. There should be a pretty thick wiring harness running just in front of that motor, and there should be a connector at about that point coming out of the harness that's just 'hanging' there. That's the test point you want to hook your dwellmeter to.

Hope that helps...