Rough running and an assortment of problems

[Isho]

I've owned my 98' SHO for over three years and had few serious problems, aside from an occasional parts hunt. A few years ago it was running a little rough and I let the dealership do a carbon cleaning. A month ago it started running rough again; I've changed spark plugs, an EGR valve, valve head gaskets - and had little improvement. In the process I noticed a large amount of carbon buildup in the intake manifold, tubing, and around the injectors. Also a few of the old plugs were literally wet with gas. It seems my chamber is building up a lot of non-combusted fuel. A trip to the local parts store revealed: IMRC stuck open, misfiring plugs (again!!!), insufficient flow in the EGR system, and failure in both O2 sensors. I guess my question is: Can someone help me make sense of all this? I have a feeling one problem is behind most of what is happening. THANX

 

[93rev2sev]

I've never owned a gen3 but to me it sounds like a bad coil...or 2.

 

[MXF7293]

If the plugs are wet they are not firing. Have you ever replaced the COP's?
(coil over plugs). The rear ones get hot and malfunction easily. That will explain some of the other things that are causing you problems.

I had some of the same problems with my 97. Check on E-bay for the COP's sometimes they are on there for a reasonable price

 

[SHOZ123]

EGR is probably the DPFE sensor.

The IRMC stuck open is from the carbon on the secondary plates. Either remove them or clean them.

O2s are from the misfiring which is either multiple coils bad or the wiring under the surge tank shorting out.