Engine idle is rough with a erratic vibration.

Also the oil pressure guage reads well above the top mark for 10-20 min after startup. Then it drops back to just under top mark

Just noticed today when I started it that some white smoke is coming out for a couple of minutes.

The engine is a L98 with 118,000 miles on it.
I am thinking that it may be time for a rebuild or crate replacement.

Opinions?

 

grey88,

Welcome Aboard![

Your rough idle can be caused by many possible problems, including vacuum leaks, poor ignition, fuel mixture problems, bad fuel, compression loss, valve train/cam problems, etc.

Your oil pressure indication is most likely a separate problem. At least it isn't indicating too low. What viscosity oil are you using? What is the air temperature? What is the RPM at a given oil pressure. Mine reads 55-60 all the time, except when the engine gets really hot.

As for the white "smoke", there is a good chance it is only water vapor, especially if it stops after a few minutes of warm up. It's been pretty humid in teh flatlands lately.

A little more detail about what maintenance you've done, what modifications there may be, and other symptoms might help. At 118,000 miles, the L98 is just getting started, unless it's been severely neglected or abused.

 

Vader,

Thanks.

The ignition or fuel should not be the problem. Replaced cap, rotor, coil, and wires 6 months ago. I checked the plugs and they seemed alright. Sitting in it for a while I noticed that it surges about 200 - 300 rpm according to the tach (can hear it also) once and a while. It does this with any fuel that is in it at the time.

I am using regular 10W-30 right now, but I think that I might switch to synthetic.

I have had the car for two years. Oil gets changed every 4 months or 3000. Picked up K&N filters for it when I did the ignition. Is far as I can tell there have been no modifications to the car except for cheap cat back exhaust setup that the previous owner put on.

 

I don't suppose you have access to a scanner, do ya? If not you may want to check for vacuum leaks.

If you choose to go synthetic, then just stick with it in order to get the most out of it. I have used nothing except Mobil 1 in my Z-28 since I bought it.

 

No, I don't have access to a scanner. I will be checking for vacum when I have time to work on it sunday

 

Also, I believe a bad O2 sensor can send erratic signal to the ECM, causing it to always adjust to maintain optimum A/F. Just a possiblity though, I can be wrong.

Also, if possible, can you tell if the idle jumping sounds like its from the fuel system or the timing? Not a very easy thing to tell by hear, but it could help.