Hello Everyone,

I am new to the forum and I am on here to help my father with his 1984 Corvette with the Crossfire Injection. A little over a month ago we had to replace the male plug to the TPS because the connections were bad. After replacing the plug the car ran GREAT for about 3 weeks, then one day driving home the idle shot up to about 1400 RPMs and we have not been able to get it to go down since. We took it to a shop called Corvette Specialty in Riverside, California where they told us that the problem was the throttle bodies needed to be rebuilt. They wanted $1,200 to do it, so we did it ourselves. Upon completion the problem persisted. We have checked for other vacuum leaks and have found none. We have replaced both IAC valves as well.

We tried setting the timing per the manual and have found that the timing will NOT stay locked into place. The retaining bolt and plate for the distributor are tight and secure, but once we set the timing to the designated 6° BTDC it will not stay there. Once set, we start the engine and take the car for a test drive. When come back and re-check the timing, it has moved. Sometimes as much as 8-10 degrees.

I am thinking that it may be a worn distributor or a loose/worn timing chain. I know how to check the timing chain, but I am not sure just how much play (if any) there is supposed to be when wiggling the distributor shaft (bug) back and forth. Any help would appreciated. Thank you in advance.

 

Did you disconnect the ESC wire for all timing checks?

I doubt that timing would cause a high idle.

 

Hi Tom, yes the Electronic Spark Control was disconnected for all timing checks and setting. Followed the book to disconnect ESC, set engine idle to 2000 rpm, and set at 6° BTDC. I don't think the timing is the idle issue. Just wondering why the timing mark would jump around so drastically once set and locked in?! Thank you for the response.

 

Either your reading of the timing is wrong, or the outer ring of your harmonic damper is slipping.

I don't see how the distributor could cause that...you'd likely see it moving if that were the case. Also, I don't think it matters what RPM you check the timing at, once the ESC wire is disconnected. At that point, the timing is static.

 

Take the electronic control module and get it tested any auto parts store can test it... also check the pick up when you have the distributor open...i just did everything your talking about to my 85.

 

Why?? How would either of those parts;
1. cause the timing to change
2. cause a high idle?

 

Tom, no disrespect intended, but I am very familiar with how to set and check timing with a light. I have been working on cars for over 20 years. I am by no means an expert mechanic, but I am also not a beginner. Your suggestion of the harmonic balancer ring being the cause is something that I never considered. I will check that tomorrow. Thank you.

 

No worries...since I don't know you, I had to put that out there as an option.

It's not uncommon for those outer rings to come loose on the elastomer/inner hub and slip. Once that happens, trying to set timing using a light is an exercise in frustration.

Good luck checking that tomorrow...let us know what you find.

 

It's possible that you have a problem with the pickup coil. I have heard of them breaking into pieces. I believe that was a problem in the '70s and was resolved by the time the C4s came out, but it's still a possibility.

The ignition module DOES have an advance curve built in to it, so RPM can affect the timing. I asked awhile back for info on that advance curve but never got a reply.

 

Check the map sensor on the driver side firewall it fixed my high idle problem

 

Thank you for the replies, gentlemen. I will check everything mentioned above.