Grant2k

My 92 RS idles fine when cold. When warm it occasionally bogs and has stalled on me twice when sitting at a light. It seems to idle the worst when I am using something electric, like the heater fan. When I turn the fan on it bogs almost immediately, then it starts to bog intermittently. If I turn the fan off it's clearly better. Also, since I got the car running a month ago after sitting for about a year, it's very slow to start cranking, then it cranks fine. I haven't load tested the battery but the battery is not old and I have filled it and have been keeping it on a desulfating charger. It's over 14 volts at idle. My dad thinks this is all related to a bad ground somewhere. Other than the main negative cable from the battery are there any other grounds that I should check that might be common points for failure? Or any other ideas as to what might cause symptoms like this?

Grant2k

A little more information that might be helpful. The fuel pump is new. The car runs great off idle all the way to redline. The only issues are with the idle.

On my drive home of about 20 miles just now it ran OK. I sat in some traffic and at quite a few lights and itdid stumble but did not stall. It idles about 600-650 RPM in gear and about 750 in neutral. I sat idling in gear and found that the radio, headlights and windows all seem to have no affect on idle. When I turn on the heater fan is when the car starts to stumble pretty bad. With no accessories on it idles smoothly but every once in a while will stumble down to about 500 RPM.

Bubbajones_ya

There are a lot of different things that can cause poor idle quality of varying degrees. Sensors, Idle air control valve, pickup coil, ignition control module, even worn cam etc etc.

Just throwing that out there because my guess may be wrong.

HOWEVER, I believe you probably have a vacuum leak somewhere with the HVAC controls.

When the selector on the HCAV controls is off, it should not be powering the fan (obviously), but also should cut off vacuum applied to the controls.

As soon as you select ANY setting (or at least MOST of the settings), then the system taps into your intake manifold vacuum. All the blend doors that control the position where the air blows out are vacuum operated. The only non vacuum operated door is the heat/cold setting which is operated by a cable.


Anyways, for the TBI, the vacuum that the HVAC controls tap into is on a small port on the passenger side behind the throttle body near the distributor. A line runs out of this and should run into a checkvalve-T splitting. That splitting sends one line all the way down to the very front bottom drivers side to the vacuum canister. It's sometimes referred to as the orb of power on these forums. The vacuum canister is directly underneath the charcoal canister, you can't see it from above your car you have to look underneath. The OTHER side of the vacuum (from the T fitting) goes into a harness that is close to you MAP sensor (which is on the passenger side above your evap housing near the firewall). TWO vacuum lines should be sticking out of that harness however. The other vacuum line sticking out of the harness (the one that isn't going to the intake manifold I just mentioned) goes to you heater core diverter valve. This is the valve with all the coolant hoses that is normally just slouching around on top of your passenger side valve cover.

This covers the entire vacuum system that is in the engine bay for the HVAC controls. The two lines that come from that harness go directly into your HVAC controls in the cabin, and there are various lines coming out of the HVAC controls to different valves to change the ducting. These INTERIOR vacuum lines rarely ever get damaged so I wouldn't bother checking vacuum on the inside until you conclude no vacuum lines are damaged in the engine bay.






EDIT:

As for your second question about grounds. The stock grounds for you car are:

- Your battery cable which should be grounded on the front bottom of your passenger side cylinder head and also have a small ground on the fender right next to the battery
- Back of your passenger side cylinder head to the firewall. There is a braided cable that connects the firewall to the cylinder head for a grounding point. Several circuits get their ground here such as your blower motor fan.
- Back of your driver's side cylinder head. I don't believe this grounds the block to the firewall/frame, but several circuits ground out on this part also.

Grounds shouldn't be causing your idling issue, but possibly could affect your starter (either that or the starter is on its way out.) I would first check to make sure the starter terminals are good and not corroded and then check those grounds I mentioned. It never hurts to buy more braided ground straps and add more grounding locations.

I hope that is clear enough. If you have any questions or want to see if I can get you a picture just let me know.


If your vacuum lines check out okay and you are sure you have no vacuum leaks, then the next thing I would probably try to do is clean your IAC valve and maybe use some sea foam and stuff.

Grant2k

Thank you, that's excellent information. I will start with checking all those items. The stalling problem has gotten worse so I've stopped driving it for now. Not sure when I'll actually get time to look at it, but now I've got a good starting point.

Ron U.S.M.C.

Alternator. If you take it into a Branch chain auto parts store they can test it or they can test it in the car.
Well I'm starting to sound like a broken record here.
I have mentioned this in two different threads in the TBI section with in the last few days.


Setting the timing and the minimum idle speed procedure. Within the procedure the IACV will be set properly.
In the end the Timing ,IACV, and the Minimum idle speed that in turn places the TPS in its proper place at the proper time.


If the thin cover over the idle stop screw is gone then there's a real good possibility its been turned. The only time it should be turned is when setting minimum idle speed.
Also if the IACV has been messed with including a replacement with out properly setting it within the minimum idle speed procedure it is not set correctly. And it all effects the position of the TPS sending an improperly adjusted system signal to the ECM. Not good.


Please take a look at these two threads and tell me what you think. They talk about the procedure and have some photos.
= https://www.thirdgen.org/forums/tbi/...ity-light.html


= https://www.thirdgen.org/forums/tbi/...idle-only.html

Grant2k

Thanks, this is all great information. I've checked the alternator when the car is running and it's charging at over 14 volts steady. I had a feeling it could be a timing issue. I did remove the IAC and attempt to "clean" it when I rebuild the throttle body. It makes sense the TPS would need to be reset. I will go through those procedures since they are likely causes.

I definitely have a vacuum leak somewhere in the heater controls based on how it runs with the fan on, but with the fan off I wouldn't think it would cause such a problem. I need to fix that but I suspect the things suggested by Ron also need attention.

Thanks for all the suggestions. I will post back when I get time to look into them. Right now I'm so busy with house projects the Camaro has to sit for another couple weeks unfortunately.

Ron U.S.M.C.

I would leave the TPS alone for now.
Is the cover still over the idle stop screw as shown in this photo ?
(It uses a star wrench.)
After the timing is set.......

If you don't have a digital tach to set the minimum idle speed than you can still do the procedure it just will not be exactly where you want it. That way at least the IACV will be set properly.

When it comes time to adjust the minimum idle screw you can start to close the butterfly's until the car starts to stall then back it out some to where it sounds right. = RPM

You should be close and the car should run better but you still need to get the Tach and do it properly.

Grant2k

I haven't had much time to play with the car so I haven't been able to check the timing or idle speed yet, but I have some new developments. I capped the vacuum lines on the intake manifold and the rough idle stopped, but what I did in the process flushed out my real problem.

Before doing anything I added more gas to the car. When I took off the gas cap I got a big rush of air. I put the vacuum lines back on and there is definitely a leak in the HVAC lines somewhere, but I'm not worried about that right now. Point is, once I opened the fuel cap the car stopped having this rough idle problem. So I have decided my issue is with the fuel tank venting. I went for a long drive Sunday and took it to work on Monday and had no issues with how the car ran, but I left the gas cap loose. I took off my vent valve and tried to clean it, but as careful as I could be I still felt like I was going to break it if I tried to take it apart. I am not sure that is the issue though because it seems like the problem is the tank isn't letting air out. Am I correct in thinking that the vent valve only lets air INTO the tank?Vapors out of the tank go through the evap system and into the charcoal canister, correct? So could my problem be the canister purge solenoid? I've been driving around with the gas cap loose and that seems to have solved my problem, so I'm guessing that is the solenoid is the likely culprit.

Ron U.S.M.C.

I replaced all of this as you can see. Inside of this valve are little springs and small rubber valves. Its a little complex sucker that I would replace. Along with the hoses while your in there. Careful not to break any "T" or plastic nipples.

Grant2k

An update on my rough idling issue: The problem seems to have gone away, possibly on its own. If I turn on the defroster it still does it, but I haven't had any problems and I drove it almost every day last week on my 40 minute drive to work. When I park, I open the gas cap every time and it hisses quite a bit and vents a lot leading me to believe it's the canister purge valve. I am going to change that valve but in the mean time manually venting the cap seems to solve the problem. I also changed the plugs which may have helped. Can't say positively that had any real effect though.

jmckelvey

Hi. I was curious to the outcome of this issue. Do you have any update? I am currently working a fuel tank overpressure on another post. There are a few similarities between our vehicle issues.... The post is https://www.thirdgen.org/forums/tpi/...ml#post6023654

Grant2k

Sorry, I haven't had time to read your thread yet but I can tell you there has been no news with my car. I haven't replaced the purge valve yet but I haven't had any drivability issues. If I drive any distance I still crack the gas cap when I get out of the car and I still get a good venting hiss. I will be swapping my axle soon and when I am under there with the car all jacked up I plan to open the connection at the soft hose on the vent line that goes to the charcoal canister and try and blow it out from the front of the car to see if it might be clogged, and at that time replace the purge valve. I'll let you know if that helps anything.