Hey everyone, I’m Kevin and own a real beauty CE with 24 kmls in absolutely original condition.

Unfortunately i do have a small issue while it idles and I can’t find it.

When the engine is hot the idle kinda stumbles a little. ~ 100 rpm.

Apparently the TBs are looking good and luckily bubba skipped my Vette. As I mentioned above the car is a 100% original and low mileage.

Cold idle seems a bit rough (ie current outside temperature) and starts with about 800 rpm and goes down to about 500 after the warm-up phase. From there she starts stumbling/surging slightly. Absolutely no loss of performance while driving or any other issues.
Cold idle has ne er been above 700 -800 rpm which seems a bit curious

I have already checked / replaced the following:

- Absolutely no vacuum leak as far as I can check/see. I staked all ports one after the other and closed them.
- Replaced gasket (fel pro) underneath the throttle plate. Right now I’m close to 18 psi vacuum at the manifold.
- EGR tested and cleaned. Looks like new, no leeks, works fine.
- CTS tested at current outdoor temperature (approx. 2.9 kOhm at 25 degrees Celsius), no further tests so far.
- Timing exactly 6 degrees before TDC
- TPS was set at 5.8v , now corrected to 5.25v
- all fluids and filters renewed
- Spark plugs, cables and distributors look like new or have been renewed before delivery.

What's left:

- Fuel pressure. However, I only have a gauge to check at the filter and can not measure between the TBs.
- I could not see any Initial squirt of the TBI , although the pump starts running when I turn the key on ignition and stops after about 3 seconds. Should the injectors not inject 2x when ignition turned on?
- I raised the pressure regulator on the passenger side slightly with the engine running, no change. Should not the engine die off?

Now the question is, are these old engines just always stumbling a bit and I expect too high a standard or is there something wrong. And if so, can you help me?

I’d really like to keep it as original as it can be, thus I don’t want to throw parts at her. I’ll take my time and check everything which is necessary.

Thanks

Kevin

 

Any ideas?

 

I have often found that fuel pressure from the in tank pumps on the crossfire engines are extremely sensitive to idle quality and starting issues. I would check the pressure before the fuel filter and see if it is with in specs.
There are several articles here about putting in later model pumps that are more reliable and slightly higher flow and or pressure.
Search for fuel pressure issues on the Crossfire system here on the Forums, and there will be recommendations if your pump is weak. Very often the fuel pressure is a culprit in my experience.
Sounds like you are methodically going through it, you will find the culprit!

Good information here: https://www.corvetteforum.com/forums...solutions.html

 

I take it that you are not getting any 'Trouble Codes' indicated by the OBD-I ECM controls....(via Check Engine Light)

 

On the 82 I had. I had about same thing. Cleaned a part on forward tb. Then always ran some marvel mystry oil in tank. About a cup a tank. Memory getting bad as it has been gone three years now. It did run nice but love the c6.

Found that repair in the crossfire section.

 

No trouble codes or CEL In gear about 500 rpm.
What could it be or is it normal?

 

Check the coolant temp sensor on the front of motor..these tend to act up over time

 

Fuel pump can cause some idle Surging..if it has never been replaced there is rubber piece that basically disintegrates with time Several other 82 owners have seen this...but if you are running good while driving and your only concerns is at idle check that front coolant temp sensor the computer reads that and if the signal is not right it can cause what your describing...

 

When diagnosing crossfire problems I remove and plug (get vacuum plugs at auto store) all unnecessary vacuum accessories ( headlights, erg, etc). MAP sensor can cause idle problems. Easy to check. is the fuel spray at the FI's nice and even- no big drops?
I also had intermittent problems which were cured by replacing the distributor module.

 

My 82 idles at around 650 ish when warmed up and in gear about 500-550..when cold about 900-1100 ..I have a new crate motor with rebuilt throttlebodys and fuel pressure turned up to 13.5..I run a 85 fuel pump as well..car runs good..I had a heck of a time getting it to run good..get a 82 corvette service manual will help a lot on this car..

 

Looking at your post you have done a lot of work on yours..I am sure you will get it.. persistence pays off in the end..

 

I will check the fuel pump and buy a new cool temp sensor.

What does the ecm need to start the initial squirts? That’s the point I’m not getting.

Thanks for your help. Appreciate it

 

I believe the computer is checking several things I know oil pressure has to be there or the fuel pump cuts out .i know if the coolant sensor isn’t hooked up the car won’t start at all..I know because I tried this..get a 82 service manual it has a lot of this info in this book well worth the investment if you plan on keeping your 82...

 

I had the same problem on my original 25K miles 82 a few months back. Took quite a while to get it sorted out. After rebuilding the throttle bodies and replacing all sensors, it turned out to simply be the fuel pump. The pump was weak and the computer was adjusting for it which caused a constant loop of idle surge then calming down. Idles perfectly after replacing the pump.

 

I always suspect the fuel pump pressure. could be low from the pump or could be low because the pickup screen is dirty.or the hose connection between the pump and pickup is bad.two places that are over looked for vac leaks is the brake booster and the headlight vac lines.