Hello Everyone

We just bought a gorgeous 86 which had been in a climate controlled environment since new. Driven VERY little with only 3700 miles.  Battery fine. Driving it back home it started to run rough after it had warmed up, but then would idle roughly and stall out completely. Fortunately, I could slip into neutral and it would start immediately back up and run.  The service engine light would flash. I bought the little GM tool to plug into the OB1 port (vs using a paperclip)  It reveals a code "51" stating that the computer ECU module / Prom is the cause.  Ive started it up several times in my garage, fires right up. However after idling up until around 130 - 150 degrees that's when the motor starts running very rough - the service engine light flashes and then stalls. Always starts right back up.  It DID have a replacement ECU installed and a new mass airflow piece replaced earlier this year. Any insights much appreciated!

Just a guess, maybe mixture or delivery of fuel. 

CONGRATULATIONS ON YOUR  CORVETTE PURCHASE. 

SINCE YOU ALREADY REPLACED THE ECU I WOULD CHECK THE FUEL SYSTEM. IF THE CAR SAT FOR A LONG TIME THERES A GOOD CHANCE THE SYTEM CAN BE VARNISHED UP. TRY REPLACING THE FUEL FILTER AND PUT A CAN OF SEA FOAM FUEL TREATMENT IN. IF THAT WORKS I WOULD PUT A CAN OF SEA FOAM IN EVERY TIME YOU FILL UP FOR THE NEXT 3 OR 4 TANKFULLS. 

GOOD LUCK. I KNOW YOU WILL ENJOY OWNING YOUR CORVETTE. I HAVE OWNED MY 94 FOR 20 YEARS AND I STILL GET EXCITED EVERY TIME I SIT IN THE DRIVERS SEAT.

Is this an aluminum or CI head version?

Thanks so much for your suggestions!

I honestly don’t know…how would I verify?  

An aluminum head is lighter and stays relatively shiny when cleaned up with solvent. A Cast Iron head will be dull when cleaned up, and heavier. Aluminum is softer and will scratch or dent easier. Cast Iron is harder, and will not deform as easy. 

Thanks for suggestion

Thanks!  Learned something new from you.  Will check next time under the hood!

Check your fuel pressure, the fuel pump has a tendency to fail. Also with that low mileage the tank has a tendency to collect moisture. You can YouTube either of those jobs, the fuel pressure kit is available at a reasonable price on Amazon. BTW you will enjoy your new addition. I started with a 1990 convertible with 145,000 miles then added a 1991 ZR-1. I never get tired at looking at how beautiful they are.

Hey! - THanks for your suggestions!  It's so frustrating as it happens EVERYTIME it hits about 178-180 degrees. Shut off - let it sit - fires right back up.  Will look into the fuel pump suggestions!  Enjoy your Vette!

Just use a magnet, won't stick to aluminum.

That sounds like the problem I had with my ‘93 but it is li  oh ely something else. The 93 cars have bad distributors which often need to be replaced. Just in case, has someone checked your distributor?

Check the idle control valve and clean the throttle body

Hello and thanks for your suggestion - turns out - the company I ordered a refurbished ECM did NOT program it correctly  - have been able to get it to run just fine and now doesnt stall out - however, it is still not programmed correctly!  The Service Engine Light stays on all the time!   So - time to remove the entire ECM AGAIN - hopefully this time the unit WILL be propertly reprogrammed.. soon!

Good Day,

Congratulations on your new ride.  Buying a classic car that has sat for some time do need some TLC to get it up to peak performance.  All the other members have made some very good advice.   I have taken care of a private car collection for some time and I would recommend changing all the motor fluids and the drivetrain oils.   The Anti freeze is often forgotten but it is important due to the rust inhibitors that break down over time and no longer provide protection and that starts to deteriorate the seals and gaskets.  The C4 Corvette is real easy to change the in tank fuel pump and completely remove all the old gas.  There are lots of you tube videos that can guide you.  The fuel injectors in the L98 motors are very sensitive to harsh fuel cleaners so be careful how much you mix in the fuel.  The injectors have coated wires inside and the fuel washes over these wires and disks and if too harsh a chemical will deteriorate the wire coating and the fuel injector will fail.  I learned this the hard way on my personal car.  Changing the injectors on a tuned port injected car is quite involved and will be a 2 day project.  

Once you get all the maintenance done these cars are very reliable and a blast to drive.   Save the wave and enjoy!!  

Good Day,

Congratulations on your new ride.  Buying a classic car that has sat for some time do need some TLC to get it up to peak performance.  All the other members have made some very good advice.   I have taken care of a private car collection for some time and I would recommend changing all the motor fluids and the drivetrain oils.   The Anti freeze is often forgotten but it is important due to the rust inhibitors that break down over time and no longer provide protection and that starts to deteriorate the seals and gaskets.  The C4 Corvette is real easy to change the in tank fuel pump and completely remove all the old gas.  There are lots of you tube videos that can guide you.  The fuel injectors in the L98 motors are very sensitive to harsh fuel cleaners so be careful how much you mix in the fuel.  The injectors have coated wires inside and the fuel washes over these wires and disks and if too harsh a chemical will deteriorate the wire coating and the fuel injector will fail.  I learned this the hard way on my personal car.  Changing the injectors on a tuned port injected car is quite involved and will be a 2 day project.  

Once you get all the maintenance done these cars are very reliable and a blast to drive.   Save the wave and enjoy!!  

I had a slightly similar problem with my 94; the previous owner only drove the car about 500 miles a year.  My car was hard to start especially when the engine was near operating temp, but it seemed to run great otherwise.  I replaced several sensors to no avail.  I took it to a REAL mechanic, and he solved my issue in no time flat.  The problem was the fuel pump.  In retrospect, I think the pump may have been compromised due to the prevalence of the corn oil or whatever they toss in gasoline now-a days.  I am not saying that the fuel pump is the issue; it might be the carb.  

Bob

Try the idle control valve 

LilRicky53

Hello, just wondering if you ever solved your issues with you 86 corvette?  Hopefully things are going well and running like a champ.