98 GTP: Replace LIM and valve cover gaskets?

[DrRadar]

I'm currently waiting for a replacement non-ported supercharger to arrive for installation in a 98 GTP that I bought earlier this year with 67k. It was rattling and when I opened it up to replace the coupler, it appeared that the rotors where clanging into each other.

Besides the rattle, my concern is slow acceleration. This GTP simply doesn't have the response to pressing the accelerator as my other GTP (99). In fact, I don't think it is responding as well as a properly-tuned normally-aspirated 3800. It runs smoothly and gets up to highway cruising speed without issue. It just doesn't jump when pushing the accelerator, either from a stop or when moving. The accelerator even feels "soft."

I realize that many things can affect the acceleration. (I'm particularly suspicious of a clogged catalytic converter, but won't be able to evaluate anything else until the car is back together.)

My immediate question is should I consider any other maintenance since I will have the s/c out, particularly anything that may affect acceleration? I'm specifically thinking of the lower intake gaskets. How difficult are they? How would a leak affect performance? I'm not aware of any coolant loss. Didn't notice any coolant in the oil for the one oil change that I did. (I've only driven it for about 2,000 miles.)

I'm also thinking of doing the valve cover gaskets, but are they that much easier with this stuff out vs. doing them when everything is back together?

A related question: The factory service manual procedure for replacing the rear valve cover says to remove the engine mount struts ("wishbones"?) then "rotate the engine for access." For as detailed as the FSM is in most cases, it doesn't say how to rotate the engine. Does anyone know?

I'm doing stuff I haven't done before. I want to be economical but not pound-foolish, and to save time in the long run. I hope to spiff up this car and get it performing sportily and keep it long term.

FYI...I chose to buy a rebuilt supercharger from ZZP because they are an authorized Eaton servicer, use Eaton parts (bearings and seals), and install new rotors in their rebuilds. It's costing about $300 more than an alternative supplier I considered, but concluded it was money well spent. I also purchased a ZZP performance PCM and NGK TR6IX Iridium plugs.

I appreciate any guidance or suggestions from those of you who have more experience with this stuff.

[DrRadar]

Decided to replace valve cover gaskets but leave the lower intake manifold gasket as is. No evidence of a problem with it and don't want to create one.

[Tech II]

I would have replaced the lower intake gasket since you had the top of the engine off. I also would check for a possible blockage in the exhaust system as far as your low power output is concerned.

[GTP Dad]

I have to agree with Tech II on this one. If you still have the top end apart change the gaskets. The new supercharger may produce enough boost to cause an issue down the road. Why tear it apart twice.

[DrRadar]

Good timing the responses, guys. I had just bolted the s/c on, so I took it off again then off with the intake manifold...and I found a Fel-Pro gasket in very good condition. (See photo.) So I'm gonna leave that gasket in and reassemble everything.

I'll check for exhaust blockage after the car is running again, if there's still a performance problem.

Many of the vacuum lines were deteriorating and I'll be replacing those as I reassemble. That may have contributed to the performance issues.

I'll let you know how it goes.