Should I replace the LIM gasket?

I’m working on a 1995 all original FD. The car has a high idle cold or hot. When hot it settles in around 13 to 1400 RPM. In neutral, if I flip the throttle at idle it will drop down to about 1000 for a half a second and then steps up to about 1300 abruptly.
i’m in the process of replacing all the vacuum lines on the rats nest and adjacent areas. Oh my question is should I go for the lower intake manifold gasket as well? I am capable of doing it, but just because I can doesn’t mean I should. Reasons to do it: I’m already halfway there. Reasons not to do it: why touch it if I’m not 100% certain that it’s leaking. And, there’s always a risk of causing more problems just getting down there and pulling the turbos off.

I have read some of the archives. What does the group think? Should I go for it or should I roll the dice that I’m going to solve the problem just by tackling all the vacuum hoses?

Your opinions appreciated.

denis

 

First off, verify for 100% that you have the old paper gasket. Many cars have had it replaced by now, it's pretty uncommon to see one still out there.

You do have to pull the turbos to do the UIM which is a big job.

Doing the rat's nest doesn't necessarily mean you are closer to pulling the LIM. There's not that much attached to it. Once the UIM is off you then have just a small handful of things, like 10-15 minutes of work, to detach. Pulling the turbos is by far the big part of this job.

Dale

 

hi Dale

thank you. How can I tell if I have paper gasket?

and what is the guidance if I do have paper?

or if I don’t?

 

You should be able to see it where the lower intake manifold meets the rotor housing. You may have to get creative to look down in there.

If you do, having a high idle is a VERY common problem with that gasket. It blows out, you have an intake air leak and the motor idles high. Totally worth replacing.

If you have the steel gasket just leave it be. I've never seen or heard of one having problems.

Dale

 

hi dale - can you make anything out from these pics?



Is this the junction?


Paper or steel?

what do you think?

 

That's the twin leaf metal one.

For all the studs, nuts and gaskets you're going to have to replace, might try a smoke test, which doesn't need a running engine, unlike some of the other diy diagnostic methods. One of the guys locally here about 10 years ago did make his own smoke generator simply and cheaply with a hand pump.

We've had the metal gasket fail and leave a trail of fuel, but that's repeated reuse....looks like that ones been undisturbed for some time looking at the manifold bolt.

 

this car was simply a daily driver. It certainly wasn’t raced or repeatedly rebuilt.

so this twin leaf metal one means the paper was replaced already. So it’s unlikely it’s vacuum leaking from here..?

 

My understanding, the paper gaskets were early in the piece and not used by 95, but open to correction. Wouldn't expect a leak.....suppose never say never though, with somebody surely to suffer the exception!

Might check the rubber ring gaskets around the primaries if running stock side feeds, seeing you're in the vicinity.

 

Yeah that looks like a metal gasket.

I recently rebuilt the engine on a '95 that had the original engine for sure and it was using a paper gasket. I'm guessing they changed somewhere along the '95 production run. I would have thought they would have stopped using them in '95.

Dale

 

Just to close out this thread, what did I ultimately do and what happened? Well I found some old documentation that showed that the lower intake manifold gasket was done, twice! In 2009 and 2010. So I decided not to touch it. Instead I replaced all vacuum lines, as well as the upper manifold gasket, and any other simple gaskets I could get to like the air pump gasket and the accelerated warm-up system. As a final result after some more adjustments, warm idle for this car settled at a super smooth 800 RPM, with no lean pops, misfires or rich bogs. Job well done 👍

 

Broke this solenoid nipple in the process. Epoxied it back into place.