Halp!

[ted g]

Good Grief-


Does anyone know if on an 86 Camaro, 2.8L 5 speed the Vehicle Speed Sensor acting up could cause an excessive idle speed? It seems to be at its worst after the car has been run for a while. I don't think it starts as soon as it goes closed loop. For some reason it takes a little while. Details follow.

This whole deal is really complex but I am trying to get this beasty to run right and pass emissions inspection.

Progress has been really great for a hobby car but I need it for transportation. In that case progress stinks.

Besides unrealated stuff like the entire exhaust system I have replaced the 02 Sensor, sealed up all vacuum leaks that I could find, new plenum throttle body and egr pipe gaskets, new engine temp sensor for the ecm, new IAC, ignition has been checked and repaired including a control module, pickup coil, plugs, wires, cap, rotor, timing has been set, actual base idle speed has been checked using the procedure in Chilton's. I have an AutoXray OBD1 scan tool.

Overall, it runs well. For one of these 2.8L engines it pulls good. The problem is the idle speed, a slight misfire at low rpm when I can get it to slow down. Other problems are all dashboard related. The temp gauge and the voltmeter peg themsleves after the car is started. If you open the dash and push the indicators back into their normal range they read properly until you start the thing. There are no stop pins in either gage. I am wondering if they were ever there or if they broke off. If they broke off I can rig up something to fix them.

On the other hand the VSS is in the dash. Is it possible that all of this is related. That is, could the VSS cause a high idle and the problem with the gauges indicate a bad ground or something else on the instrument panel.


Two wierd things coming off that Autoxray tool. Although I get an intermittant code 24 re the Vehicle Speed Sensor the scan tool reads the vehicle speed accurately. Also, for whatever reason, I believe the high idle is triggered by excessive counts on the IAC. It is reading as high as 30 at idle. This while the engine is running at over 2K RPM. On the road I have seen the IAC go as high as 69. I don't know if its normal. Logic says no but this is a Chevy not logic.

Other logic caused me to suspect the decel valve but I don't know how that would fit into the high counts on the IAC. It's just that it involves vacuum.

Anyway, if anyone has any other thoughts on the high idle or anything else I listen with great respect.

Thanks for any input.

[Morley]

VSS affect idle speed? no.

Those IAC counts are low, the IAC counts from 0-255.

[ted g]

Thanks Morley-

That explains it.

I was wrong on the maximum counts on the IAC. Somehow I got the impression that the max it could go was 70. The 255 was right there in front of me also in the scan tool's manual. I guess my bulb is a little dim these days from all this.

[ted g]

An update. So far not a lot of progress. Still runs great but strange idle business continues(erratic, starts a little high then goes over 2k when its really warmed up). I mentioned the deceleration valve (seen it called the fuel deceleration valve). I think its bad but I can't find any decent description of its function. It looks like it increases vacuum to the IAC under high load conditions and drops out when vacuum rises. Or have I got it backwards?

What I see is a large vacuum hose in coming from the main vacuum line from the rear and another out to the line going to the IAC. Then there is what I believe is a signal port. It connects to a vacuum line going around past the throttle body and back to the main vacuum takeoff on the engine. In any case when I checked yesterday I got full engine vacuum coming out of the signal port. That would seem like some kind of broken diaphram. Then I disconnected it from the hose leading to the IAC, plugged everything and the engine seemed to react by running a better. and slower. On the other hand, just before I shut it off, it started to idle too fast again. I'm going to do it all again. Maybe I'll see something different.

I did try to get another one of the valves locally and on line. I figured if it can be gotten for $20 or so it beats playing around with it. The dealer can't supply it and very few others ever heard of this component.

If anyone is watching this thread and has any ideas I am a good listener.

Otherwise, have a good weekend to all. Look for me in the junkyard trying to find one of those valves.

[[email protected]]

Originally Posted by ted g

An update. So far not a lot of progress. Still runs great but strange idle business continues(erratic, starts a little high then goes over 2k when its really warmed up). I mentioned the deceleration valve (seen it called the fuel deceleration valve). I think its bad but I can't find any decent description of its function. It looks like it increases vacuum to the IAC under high load conditions and drops out when vacuum rises. Or have I got it backwards?

What I see is a large vacuum hose in coming from the main vacuum line from the rear and another out to the line going to the IAC. Then there is what I believe is a signal port. It connects to a vacuum line going around past the throttle body and back to the main vacuum takeoff on the engine. In any case when I checked yesterday I got full engine vacuum coming out of the signal port. That would seem like some kind of broken diaphram. Then I disconnected it from the hose leading to the IAC, plugged everything and the engine seemed to react by running a better. and slower. On the other hand, just before I shut it off, it started to idle too fast again. I'm going to do it all again. Maybe I'll see something different.

I did try to get another one of the valves locally and on line. I figured if it can be gotten for $20 or so it beats playing around with it. The dealer can't supply it and very few others ever heard of this component.

If anyone is watching this thread and has any ideas I am a good listener.

Otherwise, have a good weekend to all. Look for me in the junkyard trying to find one of those valves.

First of all, you need to get the bizzare dash instrument thing figured out before you try to diagnose any computer/sensor related problems. All the dash warning lights etc.. are also tied into your logic sequence. Try this to give you a better understanding of whats going on:

Ground the diagnostic terminal of the ALDL.
Turn ignition on (don't start).
Wait at least 30 seconds.
With ignition on, unplug the IAC.
Remove ground from ALDL
Start engine.

It should now idle right/half assed/or not depending where your idle screw is adjusted at. Also make sure your TV cable is adjusted properly.

I hope this helped.

[ted g]

Thanks for the suggestions. I'll give it a try.

I am with you on the dashboard thing. The VSS is connected to the dashboard on this Cam. I checked the trans and all I found was the backup lights connector. As a result I have been studying the wiring diagrams of anything going to that dash. I was starting to think it wasn't supposed to have power when the starter was turning. According to the orginal electrical troubleshooting supplement from Chevy I have that one wrong. It's all hot in start and run.

So my thinking right now on the dash is running in a couple of different directions.

1-A ground or short problem. The two gauges that are acting up are the voltmeter and the temperature gauge. They both seem ok until it is started. You can turn the key on and off twenty five times and no problem. I think, and I have to verify this one, that the two gauges go off scale after the engine is started. What is unclear is when it exactly happens. That is whether its after the first start or ???.

2-Maybe the gauges are acting relatively normally. They have little bumps where you would expect stop pins to prevent overtravel of the needles. If they were there and broke off that would explain it all. They might take some use and eventually jam at an extreme if they need stops. The way I can get them working is to pull the bezel and plexiglass cover. Then if you give a push back into the normal range they start working.

3-Give up and buy myself a new mountain bike to get around until I find new, reasonable, employment. Then I could go the route I was really planning on which was a new vehicle for transportation. That would leave me time to straighten out my Camaro toy.

Of the three choices I am thinking its number 1.

Thanks again.

[ted g]

I took a closer look at the actions of the gauges. What I have found is the bad behavior happens when the ignition switch calls for the bulb test. As long as you don't turn it to the start position the gauges stay totally normal. Hit the point where the bulb test occurs and the gauges go nuts. This will happen even with no foot on the clutch and no starter action. The temp gauge goes way past where it belongs and jams on its housing.

Looking at the wiring diagram there are two sources going to the gauge that seem to give it ground. The first is the sensor. But the sensor maintains enough resistance even at overheat so it doesn't peg the gauge.

The second ground source looks like it comes from the bulb test. That would seem to give it full ground. On the other hand there may be a solid state device there someplace to prevent that from happening. So far I see nothing.

AT this point I am in the "what is this" mode. I don't get this one. I have some more diagrams to paw over this evening. I guess that's tonights entertainment. Boring ain't it?

[ted g]

Ok-Now the dash problems are mostly under control. I fixed the problem of the temp gauge pegging itself on start by disconnecting the "bulb test" lead from the ignition switch. Now the gauge works without any insanity. The voltmeter seems to be working, at least for now.

The voltmeter may be working better from additional cleaning of the contacts for the instrument panel.

The Vehicle Speed Sensor(On the instrument panel) is still a problem. Around the time the car warms up enough to go closed loop the check engine light will sometimes come on. It is sending a code 24 (Vehicle Speed Sensor). I checked the resistance to the ecm, seems ok now. It was very slightly high, until I scrubbed the contacts with rubbing alcohol. That seemed to clean up its act. I also cleaned the parts of that little propellor inside the speedometer. I imagine its used to make and break the optical sensor for the VSS. Checked all the connections on the VSS. Didn't clean the emitter out of fear of breaking it. That code 24 seems to be preceeded by a high idle. It revs up to about 1.5-2k just before the light comes on. Wierd. The scan tool I am using can read the sensor. It is indicating the correct speed when the car is moving.

I will probably have to go for the new sensor even if I am concerned that I may have missed something. I am out of ideas on how to get rid of the code 24 using any other method.

Again, any ideas are appreciated.