ead94z28

Ok, I have been dealing with this for too long. The car has a horrible idle in drive with my foot on the brake. Shakes like crazy. I also hear a knocking sound coming from the bottom or the engine area. In neutral the car shakes quite a bit and I still hear this knocking. Acceleration is good and high speed driving is great too. I took it to the dealer and they spent a long time diagnosing this and came up with a possible spark knock, but they arent sure. They said all they can do is hit and miss replacement of stuff...so I started replacing stuff.

Opti
Plugs
Wires
O2's
CAT
IAC, EGR, TPS
Coil
Fuel filter
Cleaned TB and replaced gaskets
Compression test OK
Injectors tested fine

They said spark knock as a possibility. Do you think I should replace the knock sensor? I am running out of things to replace! The dealer also mentioned maybe a new PCM, but they are pretty much shooting in the dark. There are no SES lights and the dealer scanned it and there were no codes. Please, any suggestions? Should I go ahead and do the knock sensor and the PCM?

Thanks

Injuneer

Ever do a data log? Checked it for knock retard? That would tell you if knock is a problem. It would also allow you to examine the long term fuel corrections, to see if there are exhaust leaks or misfires indicated. By "Injectors tested fine"... do you mean the injectors were removed and flow tested for flow rate and spray pattern, or they just hooked up a 'noid light and found the injectors were pulsing?

Has anyone considered the possibility of a mechanical problem causing the knocking sound from the bottom of the engine... bad bearings, loose flywheel, broken damper?

Looks like the typical Mr. Goodwrench "replacement parts" approach.

ead94z28

They actually removed the injectors. They also checked every inch of the car for the knocking and couldn't find anything. I also had it at the exhaust shop and they found two leaks and fixed them, but same problem. This is the dealer so I figured if they have no idea, who would?

ead94z28

What exactly is a damper?

Injuneer

Its attached to the front of the crankshaft. "Dampens" crankshaft harmonics. In the LT1, it is also the drive pulley for the serpentine belt. If it is loose or broken (there are two concentric iron rings, connected by a rubber ring between them) it can cause a knocking noise and knock retard.

ead94z28

Is there a way to do a visual check on it or pull on it to see if it's loose?

ead94z28

Injuneer, I looked at the damper and it is moist with oil around the backside. Is this a normal seepage or should I be concerned?