Drive it & Vets Vet: I already have a Zurich ZR13 ODB2 reader from Harbor Freight that I use on my newer vehicles. It doesn't plug into the ODB1 diagnostic port on my 1986 Corvette. The ZR13 reader will display live data if its available. I can purchase a ODB2 to ODB1 cable converter for GM vehicles from Amazon. I'm considering purchasing it for $9 and giving it a try. The ODB1 connectors provide limited data from what I understand, since computer technology was in its infancy at that time. It sounds like you have experience with this and it should give me some type of live data, right? I read the reviews on the ODB2 to ODB1 cable converter at amazon and many of them said they couldn't get live data. Here's a link to the converter cable:

 

I can't say on the adapter cable working as I've never used one. I've always used an OBD1 scan tool or Diacom on an old laptop. You do get plenty of live data to figure out problems-though the newer OBD2 does give more.

 

Don't waste your time or money on the Zurich. I am not the one to guide you into OBD1 land but you need to understand you need a dedicated OBD1 data scanner. There are a lot of adapters, and code readers and crap out there that make you think they will and none will help except an OBD1 data scanner. there are $9 and $30 code readers, they are nothing more than paperclips to short 2 pins together so you can watch the car blink numbers at you and tell what number code you have. The previous post I gave has 2 of the very few methods unless you have a pretty expensive and or old dedicated OBD1 scanner or some $2400 snapon scanner. You are in for a learning curve so don't start out spending 2 weeks learning the hard way like I did.
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I replaced the Idle Air Control (IAC) sensor this past weekend. There was some carbon build up on the old one and the problem didn't seem as bad, but its still there. I got a service manual and I found a troubleshooting guide for what sounds like my problem. The book called it "idle hunting" with occasional stalls, which is what I've got. It suggests that I check the PCV valve. That's easy enough, so I'll try that next. There should be a 90 degree short hose that connects a PCV tube to the throttle body. Somebody put in a straight hose and its crimped where it curves. I'll try replacing that hose and the PCV valve and I'll see if that has any affect. I can get both for $20, which is not that expensive. I'll let you know what happens.

 

Hello disney1984, so you have had your C4 for 6 months. Just a few days ago I sent an email to the general manager of a local Chevrolet dealer. I asked him some questions about my C4. Very politely he informed me that his Chevrolet Dealership does not service any Corvette older than a C5. So maybe you should sell your car and but a newer one?
Also you do not need a OBD 1 code reader, all you need is a short piece of wire. You read the codes by counting the flashing "service engine" light on the dash. You do need the book that tells you the codes, etc.

 

Thank you for your comments JimBobPrime. The Chevrolet dealers in my area won't service my car either. I also have an older 1986 Dodge Ram 1500 that the dealers won't touch. I've heard over the years that dealers generally won't touch vehicles over 10 years old. I think its sad they don't support their own products for the life of the vehicle. I purchased this Corvette mainly for my son. My thoughts were it would be a great first car for him, and I could teach him about mechanics as we work on it. Its unfortunate for him, but he won't be getting a new Corvette. He does love the one he has, if we can just get it to run right. The car didn't have this issue when we purchased it. This problem is a little more advanced than what I'm used to dealing with. I have an older ODB1 plug in tool that allows me to flash the codes. There are no codes in the system, which is making the problem harder to diagnose.

 

Another common problem that effects idle quality is when the throttle body gets gummed up with carbon deposits. Prop it wide open and look in it. It can take a brass brush and spray cleaner to get it out. If you're going to keep it you really have to get an OBD1 scan tool..

 

Thanks Drive it. I've already looked in the throttle body and it looks fairly clean. There are also no tears or holes in the plastic piece connecting the throttle body to the air filter.

 

Hi, search Youtube using these words lto read codes :

<How to use OBD1 Code Reader 82-95 GM Cars>

 

Hi, I understand very well what you are talking about. I learned on my 1957 Chevrolet and my 1959 Volvo 544. So maybe you should start with an older car or something more basic. Including how to read schematics, use tools, etc. Even schooling in electronics, test and measurement equipment.

Nothing about cars is simple today.
Good luck

 

I have the same problem in my 86.
I have a modern engine management system (Megasquirt) and I have a MAP sensor in use, so of course it is a little different than yours.

The idle went up and down until the engine died.
And I also had a problem when the engine temperature got high enough.

Another problem I had, the gas stuck on at times.
I noticed that when I moved the throttle shaft forward and backward by hand, there was a lot of looseness.
My suspicion is also the IAC.

I bought an almost new BBK 58mm throttle body from my friend and installed it.
I live so far north that I didn't get out much to test the new throttle body until it started getting too cold.

Here's the log with the old and the new throttle body and at least I didn't get idle hunting to happen yet.
I have to continue the test again next spring.
I managed to drive for a few days until the weather got too cold, but the idle worked fine.

Sorry that the temperatures are in Celsius
CLT = Coolant

 

I have an update for everyone. First, I would like to say I have a love/hate relationship with this car. I love how it drives and looks, but I hate how it seems like it's one problem after another even though the engine only has 86,000 miles on it. Many repair shops won't work on it because of its age. This is not a daily driver for me and that's why it's taken me a while to post an update. I installed a brand-new IAC, which didn't correct the problem. The old one had some carbon on it and it looked like it needed to be replaced anyways. I replaced the PCV valve, grommet and a couple of PCV hoses. I started having smoke come out from back of the engine and underneath the car while testing it. I knew the valve cover gaskets were leaking, so I figured that was the problem. I figured oil was dripping at the back of the engine on the exhaust manifold. I didn't want to run the car long enough to test the idle because I was afraid the oil would ignite. The smoke was that bad. I researched the forum and ended up replacing the valve cover gaskets myself using the thinner Fel-Pro VS12869 gaskets, which leaked horribly after installation. Both sides leaked. I have iron heads and the top of the heads have a rounded surface where the cover meets the head. I think this is why it leaked. I decided to go with a thicker valve cover gasket that would conform to the shape of the heads better. I ran out of time to work on the car myself, so I worked out a deal with a local automotive repair shop. I removed both valve covers and had the car towed to their shop, which was cheaper then having them remove the valve covers. I knew the head valve seals were leaking and the owner of this shop had the expertise to replace them without removing the heads. I decided to replace them with the valve covers already off. He removed the spark plugs and used compressed air to keep the valves in place. I didn't trust myself to do this. I could visualize the valve dropping into the cylinder and I didn't want to take the chance. They replaced all of the valve seals and installed the Elderbrock 7549 valve cover gaskets with longer studs (Moroso 68820) that I had purchased, which worked out great. I had also removed the EGR bypass tube when taking off the valve covers. I didn't realize there was an electrical connector to the heat sensor located in the EGR bypass tube and I thought it disconnected at the sensor. I ended up pulling the tip of the sensor off. I couldn't find a new sensor anywhere, so I ended up purchasing the whole tube from Covette Central, which came with the sensor. The compression clamp that came with the EGR bypass tube couldn't be crimped well because of its design. I kept an eye out on Ebay and was able to pick up three original GM clamps. Installing the EGR bypass tube wasn't as bad as all the posts say, but it wasn't fun to install either. Anyways, the auto shop gets the valve seals, EGR bypass tube and valve cover gaskets installed. I also had them install a new GM TPS because the voltage on my existing one was too low. I had them set the voltage on the new one according to the service manual. I go to pick up the car. The mechanic tells me they noticed the rear transmission seal was leaking and its located right over the crossover on the exhaust. It was creating a bunch of smoke. So frustrating, and I thought the smoke was coming from the leaking valve covers. Then they tell me the new PCV valve I purchased at O'reilys isn't working. Wow, really? They didn't have time to fix the transmission leak, so I took it home and purchased a new old stock ACDelco PCV valve off Ebay. The engine idle was still oscillating badly while driving it home from the shop. I installed the new PCV valve and the oscillating idle problem seemed to go away. About 3 months later it started it again, but only slightly. The idle oscillates between 600 and 700 RPM on occasion, but at least the engine no longer dies at a stop sign. Some of the vacuum hoses look a little questionable, so I'm going to replace some of them to see if the idle improves. I took the car back into the shop and had them replace the rear transmission seal and that fixed the smoking problem. Can you feel my pain?

 

Just to be sure, you meant to say 600 and 700 RPMs, right? If that's the case, then I wouldn't even worry about it but 6K+ should make an L98 explode.

 

Right, I need to edit my post on the RPM's. Thanks 2011KLR. This is my first C4. Is it not uncommon to have a little oscillation during idle? I'm just worried about it starting to die at stop signs/lights again. Although, it doesn't seem that bad other than the engine sound oscillating back and forth. It's starting to cool off now that its October. I'm wondering if the cooler weather is affecting the engine. Does the computer constantly learn and adjust the idle based on the input from the various sensors? Could the computer be learning how to idle with the cooler weather and could the idle eventually work itself out?