I have a 1982 Corvette with 25K original miles. After buying the car about a year ago I had basic maintenance done on the care including
- replacing all hoses and belts.
- radiator flush
- new thermostat
- new spark plugs
- new spark plug wires
- all engine leaks reparied
- new air filters

For the last few months the car has been idling very rough and the RPMs fluctuate like it's hunting for the correct RPM, especially before going into closed loop but after warmed up also, though not as bad.

I took it to a reputable local Corvette shop where they have been trying to get the idle smoothed out and just generally get it to run better. They've had the car for 9 weeks now with minor success. I'm not an engine mechanic but I'll try to describe what has been done so far:
- every sensor, including the throttle position sensor has been replaced.
- fixed an intake leak
- swapped out the ECM
- rebuilt the throttle bodies
- adjusted timing

The car runs a little better but is still running rough and idles at about 700 RPM in park (which I think is too high) while still fluctuating within 100 RPM's up and down (600 - 800).

The mechanic is out of ideas as what to try next. I thought I'd open it up to the experts on the forum for anything you could recommend he try.

Thanks for suggestions.

 

The fluctuation would be caused by the IAC motors and probably because of a vacuum leak. The usual place vacuum will leak is where the MAP sensor's 7 mm hose connects to the rear of the left throttle body. The OEM hose is a cheap hose with no internal or external plies so it'll split where it makes the connection. Replace it with an ordinary 1/4" fuel hose as that will last virtually forever. Also I suggest snugging up all of the intake manifold lid bolts in case they have loosened because of the gaskets shrinkage. Have you also replaced the O2 sensor? It needs to be replaced every 25,000 miles because they don't last much longer than that and they'll also cause a poor idle.

 

I did not read that they checked your fuel pressure....which DOES require the fuel line that joins the two throttle bodies to be removed. I had a 1984 that was doing the same thing. The idle would 'hunt'. Once a new fuel pump was installed and other things verified...it idled like a dream.

Did this company PROPERLY adjust (balance) your rebuilt throttle bodies using a manometer??? I can say that I have had a customer SWEAR that using a piece of paper does it...UNTIL I bring out my manometer and show them that the manometer is much more precise.

Curious...what is your MAP sensor showing on the scanner in volts???

DUB

 

your idle in park is not to high .it is controlled by the computer.the surging of a hundred rpm can be normal .the computers they had were slow.I would drive it for a few hundred miles and see if runs out better.lots of people have drove them selfs crazy trying to get a crossfire to run perfectly smooth ,not sure its always possibile.one more thing you can try is new injectors.

 

vacum leaks

 

Thanks for the suggestions. I passed this thread on to the mechanic and the service writer.

 

The Crossfire is known to have a funky idle. Its the nature of the CF.Even when new. I have an 84 that is the same after replacing everything.

 

See my comments under the cfi bogging thread. Post #22

https://www.corvetteforum.com/forums...em-help-2.html

 

I've never heard that before. Why would it have a funky idle? Mine never did nor has anyone else's that I know of.

 

I have several customers with the Cross-Fire engines and they idle fine...and preform excellently...and others...that need a lot of help.

DUB