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Miss at idle and dies coming off highway.

CROOZ1N

Well-known member
Joined
Apr 16, 2008
Messages
106
Location
Roanoke VA
Corvette
1993 Torch red coupe
Hello Gentlemen,
This forum has come thru for me many times and I am here asking for some help again. The vehicle I’m working on is a 1993 coupe automatic with 124K. I am unsure of the heritage before I bought it about 3 years ago.
The problem is a miss at Idle but it’s very sporadic .I can be stopped waiting on traffic and I’ll feel a miss under my foot coming thru the brake pedal. Many times if I’ve been on the highway for a good while and exit, the car will simply die at the 1st stop light or end of the off ramp. This is very disconcerting to the wife and causes much panic whenever it stalls. It has however always restarted. I checked the Injectors for proper resistance and they all checked to manual spec. I do have the service manual as well.
I have downloaded and begun to study using datamaster software to look at whats happening with the car.
There are no codes stored and other than this little problem the car runs fine. I know that opti cap and wires were replaced by the PO and a PCM forless chip installed. Maybe for a rear end change. He went from the 2.59 to 3.07 I think.
I had a problem with it last spring in the coil crapped out and I had to go thru 2 garages before I got it fixed ( it was an out of town failure or I would have worked on it myself) the first place blamed the VATS but said they didn’t know what it was eventually.
Some AC problems the GM Junkie helped me work thru but for the most part shes been trouble free. As I said before I’m just starting using Datamaster so I still need to learn what I’m recording and how to interpret it. As a little background I have worked as a mechanic deisel and Automotive, and now as an Industrial Electronics Technician so I can be taught and know my way around a toolbox as well as a laptop.
Any help you can offer will be appreciated.
 
Hello Gentlemen,
This forum has come thru for me many times and I am here asking for some help again. The vehicle I’m working on is a 1993 coupe automatic with 124K. I am unsure of the heritage before I bought it about 3 years ago.
The problem is a miss at Idle but it’s very sporadic .I can be stopped waiting on traffic and I’ll feel a miss under my foot coming thru the brake pedal. Many times if I’ve been on the highway for a good while and exit, the car will simply die at the 1st stop light or end of the off ramp. This is very disconcerting to the wife and causes much panic whenever it stalls. It has however always restarted. I checked the Injectors for proper resistance and they all checked to manual spec. I do have the service manual as well.
I have downloaded and begun to study using datamaster software to look at whats happening with the car.
There are no codes stored and other than this little problem the car runs fine. I know that opti cap and wires were replaced by the PO and a PCM forless chip installed. Maybe for a rear end change. He went from the 2.59 to 3.07 I think.
I had a problem with it last spring in the coil crapped out and I had to go thru 2 garages before I got it fixed ( it was an out of town failure or I would have worked on it myself) the first place blamed the VATS but said they didn’t know what it was eventually.
Some AC problems the GM Junkie helped me work thru but for the most part shes been trouble free. As I said before I’m just starting using Datamaster so I still need to learn what I’m recording and how to interpret it. As a little background I have worked as a mechanic deisel and Automotive, and now as an Industrial Electronics Technician so I can be taught and know my way around a toolbox as well as a laptop.
Any help you can offer will be appreciated.


Interesting...
seems like the TCC would hold it in gear. The engine should stay engaged and brake until the brake pedal is used. That should prevent it from stalling until near idle speeds.
Mine stays locked in until we run down to around 8-900 rpm, then it will release if I have not tapped the brakes.


Ohm ok'd injectors can still be dirty injectors. I'll go ahead and upset a few folks and advise some Marvel Mystery oil in the gas to see IF that makes any difference. These stock injectors seem to have a limited lifespan, time or miles. If you decide on new inj, everyone here has had outstanding success with Jon @ FIC. Under $250 with gaskets, O-rings etc. Check out his You-Tube videos under "fuel-injectors". Very educational.:cool!:
Back on topic...

I'd go thru ALL of the grounds on everything. There are MANY, so track them down and clean, inspect and tighten. Plastic cars take lots of grounds. ECM controlled cars require even more. The vette electronics are managed by ground path completion, so resistance is important as are good connections so the values stay stable. Power is ever present and grounds are used to manage every type of servo or control there is.

Next, go thru the vac lines, especially the EGR solinoid. If the EGR is stuck open just a bit, it will cause everything that you describe. Get a small mirror and some fresh vac tube and just suck on the tube to the EGR valve,. thats enough vac to see if it moves or not. Place the mechanics mirror under the edge of the bonnet so you can see if the diaphram tries to move.

Might pull a couple spark plugs to see what kind of shape they are in. Opti's are good for mystery misfires, but they are too expensive to throw money at them. Go thru all this other stuff first and rule out the Opti-Spark.
Hope this helps !
 
Can you post up your scan results...

Does the readout give voltage equivalents? Or absolute values? Like below: (never mind my scribbling notes)

1687_4929b014c1f6d.png
 
My vote is with Junk. I found that I could clean my egr using Easy Off oven cleaner. I sprayed it liberally into the egr and let it sit and then rinsed it with hot water. A note of caution when you rinse it out be sure the wife is not around and that you are prepared to clean the sink. I could not believe the crud that came out with the flushing. When done push the plunger in and out and then put some light oil in the cavity for the pintle it should not leak out but if it does just repeat the clean and flush a couple of more times.

Oh and if your 93 is like mine you will discover that the bolts holding the EGR are 3/8 and not 10MM. Use care not to strip them out (Don't Ask)
 
Yup you did hit the coil as well Junk. You've been a BIG help with this car and my education about it and I thank you.
For those that may not know Datamaster software lets you record a session and be able to play it back. I can send the UNI file to anyone that would like to take a peek at it or I exported it into a CSV file but it has 2300 data points so posting it here probably won't work. But I'd love to have someone look at it that can say " see at Data point xxxx the car is doing this and it should be doing that because this BLM is leaned out due to ,,,
Clean the EGR - OK. Will do. I did find a bad vacuum hose on it a couple years ago it was throwing a 32 if i recall.
I have checked SOME of the grounds and will check the others as I can. Maybe this week. I worked on the C5 yesterday. changing the oil and doing some extra cleaning so time got away from me. I ran the C4 yesterday after adding some techron Injector cleaner and she ran fine but I know its not "Fixed" yet.
 

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uhhh..hmmmmm..

Post # 2, first response to original query, paragraph 4 :D
 
Yes Boom driver I saw that but until today had not had time to play with it. I removed the EGR and cleaned it with a couple different cleaners Throttle body and carb cleaner then a parts cleaner then Finished it up with brake cleaner. The pintle moves freely and some carbon came out but not a bunch. I replaced the vac hose going to it as it broke when trying to remove it so it could have been cracked before. I had to Jack it up as i dropped one of the AIR hose clamps on top of the tranny and had to go under to fish it out. So while under I removed the ground strap on the bell housing and cleaned it up.
I searched for the connection John talked about in the wire loom on the right side but did not find it.
Once I had it all beck together I started it and as it ran I turned of fthe light and looked for arching .. Didnt see any. I also lightl shot some starter fluid around the vacuum hose connections around both sides of teh engine and listened for higher Idle. None found.
The next step I suppose it simple to run it and see how she does.

I'll also do another data logging session and see if anything comes up.
 
Yes Boom driver I saw that but until today had not had time to play with it. I removed the EGR and cleaned it with a couple different cleaners Throttle body and carb cleaner then a parts cleaner then Finished it up with brake cleaner. The pintle moves freely and some carbon came out but not a bunch. I replaced the vac hose going to it as it broke when trying to remove it so it could have been cracked before. I had to Jack it up as i dropped one of the AIR hose clamps on top of the tranny and had to go under to fish it out. So while under I removed the ground strap on the bell housing and cleaned it up.
I searched for the connection John talked about in the wire loom on the right side but did not find it.
Once I had it all beck together I started it and as it ran I turned of fthe light and looked for arching .. Didnt see any. I also lightl shot some starter fluid around the vacuum hose connections around both sides of teh engine and listened for higher Idle. None found.
The next step I suppose it simple to run it and see how she does.

I'll also do another data logging session and see if anything comes up.


ok,

but did you check the EGR to see if it actually works? by applying vacuum and seeing the pintle or diaphram move? Being free does not mean the diaphram is intact. It takes very little vac to make it respond, and the path thru the EGR solenoid has to be good as well. The solenoids fail too. Check that with vac and apply voltage to see if it opens or not.

Be VERY VERY careful with the brake parts cleaner...it destroys many types of plastics. Absolutely corrupts the integrety of the plastic and it crumbles. Does that to seals, wire insulation and plugs too.

Same goes for starting fluid...What happens IF you find your arcing when you're spraying starting fluid? :ugh end of problems........

I saw a picture of a starting fluid mishap on a C4. Front of car burnt to the ground, two buddies without their shirts looking at the mess that insurance would not cover. They tried to use their shirts to beat the flames out.:chuckle
 
The wire bundle on the right side under the rocker cover is inside the large wire harness that runs back towards the firewall.

http://i285.photobucket.com/albums/ll72/John-68/CorvetteTPS018.jpg

If you look at this picture and follow the two black wire looms back to were they go into the large black wire loom that is were the ground bundle is at the junction of all the smaller wire looms that come together there. This picture is one I had and but I hop it will help you.
 
sorry that I forgot to say that .yes the EGR works. Thanks also for the heads up on the starter fluid. I was using small bursts around the upper areas only but its a good point about arcing. :ugh And yes I was somewhat corceren about what cleaner would work but didn't have any Easy Off , Heck If easy off wont hurt it then I didn't figure Carb and choke or Brake cleaner would be nearly as harsh. I've seem electrical contact cleaner at work just disintegrate electrical connections before so i know of what you speak.
John I'll look at that side again the wire loom is crispy so I didn't did too deep as I don't have replacement loomage. 'll see about picking some up today.
Thanks again to you guys.
 
sorry that I forgot to say that .yes the EGR works. Thanks also for the heads up on the starter fluid. I was using small bursts around the upper areas only but its a good point about arcing. :ugh And yes I was somewhat corceren about what cleaner would work but didn't have any Easy Off , Heck If easy off wont hurt it then I didn't figure Carb and choke or Brake cleaner would be nearly as harsh. I've seem electrical contact cleaner at work just disintegrate electrical connections before so i know of what you speak.
John I'll look at that side again the wire loom is crispy so I didn't did too deep as I don't have replacement loomage. 'll see about picking some up today.
Thanks again to you guys.


I learned the hard way about brake cleaner...
I sprayed some inside a control box for a piece of equipment (many yrs ago)and the plastic switch housings ($600 each) turned to crumbs if touched...the boss thought someone must have dropped it from the 3rd floor. Who was I to ruin his theory with the truth?

I also learned over the yrs that the chemical degreasers and cleaners that we love to use under the hood, are what hardens the wire insulation as its exposed to heat. Everything has oil in its chemical make-up, and these chemicals remove that vital oil from the plastic insulation and it hardens, cracks and causes all form of grief somewhere down the road.
We used to use an outstanding degreaser in our shop....the stuff would break up grease (wads) of the nasty stuff you find on truck axles or old engines and such. It melted the crud off. If a drop of it hit something painted, it also removed the essential oils in the paint and it would peel the next time you rubbed it or washed it.

So now, its simple green, or just hi pressure water under the hood. Good steam when I can find it works better than anything. I've got some crispy harness myself and its from the chemicals. GM also had some bad wire they used back in the c4 days that failed to meet the gov guidelines for minimal age or endurance.

Crooz..

Has the TPS been checked? has that been checked for the spec at idle? If its set too low it could be killing fuel whenever you let off the gas. Also check it for a dead spot in its travel thru the range from idle to WOT.

Also, back to wire-rot and insulation, I just battled this on mine, It had the left side injector harness with bad wire or cracked insulation that was causing a misfire that moved from one cyl to another. After I figured out what was happening, with all sorts of odd symptoms I chopped out the bad sections and soldered in new, added new inj plugs and all is well. I still have an issue with wire rot in the firewall harness that effects the oil press sender but that works right IF you get the harness moved in the right spot where it likes the contact it has....
 

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