Ok i just bought my vette 85 C4 from a friend and i am noticing that the idle jumps alot and when you first start it the idle jumps so much it almost dies tryign to find out what might be wrong with it? and what the cure is.

This is the exact problem i am having. Let me tell you what ive don and what im down to doing.

I have replaced the; Computer, M.A.F, engine temp sensor, coolant temp sensor, plugs (3 times now), wires, cap and button, rotor, coil, ignition control module, fuel pump, and fuel filter all in the effort to fix the same problem. (sometimes it was broken down over one of these problems.) None of this even came close to fixing the problem.

Last problem i have had so far was that my pre-cats clogged up and the car would not start. I cut thoes off. When I had the exhaust system cut off I started the car to be sure the cats were the problem. Not only did the car start easier and faster than it ever has, I did not have any problem with a rough idle like you are describing. However When i pul it all back together, omitting the pre-cats and stright piping them I am still having the same problem. I will be replacing my Main catalitic this weekend.

CAUTION!!!!
Removing catalitic converters is illegal by federal law, and you need them to pass emitions. that statment is truth.

This statment is speculation. I dont think that removin 2 out of the three catalitics is going to get you in any trouble. Because you are still running on a main catalitic. All I know is the few muffler shops i went to said that they were not sure so the would not do it. I took the chance and did it my self. (sounds better too) I dont think there is a problem with it but I have yet to get an official word on it yet. Most cars only have 1 catalitic converter dont know why we would have to have 3.

Qucik rundown on price. To replace your pre-cats $85 ea.(Auto Zone), or removing a stright piping mine cost me $35 for the 2 18" pieces of pipe i needed flared from miankee. Your main cat' $180 (Auto Zone), $135 (Ebay - new including shipping - if you can find one), $113 plus tax and shipping (I think it was Corvette central)

Hope this helps you.

Hello, I actually removed my precats because they were clogging my main cat. I have never had a problem passing smog. Came close though. Make sure the vehicle is hot when testing. The car does have more power with the one cat only. Regarding the Idle, my 86 does the same until warm. I believe it is caused by the Idle air control valve. I was running my vehicle without a MAF sensor for over a year now basically on default value and it ran great. When I replaced the MAF, all codes went away but my idle when cold began to bounce around. I will be following this post definitely.