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Dear Jim,

I had an engine replacement done on my 1995 Honda Civic (1.6L, L4, 5-speed manual) about 2,500 miles ago, and now it's having a few problems that have started all at once.

First, the idle sometimes goes up and down, especially after starting up. The car also loses power suddenly when the RPMs get high in any gear, and a couple of days ago I noticed a rough sound to the exhaust as well.

Do you think this could all be because of a bad catalytic converter?

-- Ed Rolandera

It's possible, bro. In any case, this is one of those perfect times to talk about the true nature of automobiles.

We tend to look at a car and see just one big, complicated mess of bolts, hoses, wires and sheet metal, but it's really a simpler beast than that -- a collection of individual, separate systems that all work together to create motion.

When one of these isolated systems breaks down, other systems can be affected, and the performance of the entire vehicle suffers. Often, the key to diagnosing multiple problems like yours is to narrow the possibilities until you finally hit the root cause. After that, all the satisfying wrench-spinning and knuckle-banging can really begin.

I'd say go with your first instinct on this one. You mentioned the catalytic converter -- part of the exhaust system -- so why not start there?

A mechanic or knowledgeable friend can show you an easy way to temporarily separate the exhaust manifold from the rest of the system to check for a blockage. With this done, drive around the block. It'll be loud, but if the engine runs well, you just found the problem.

If not, check out the fuel-delivery system with a pressure gauge mounted to the fuel pressure valve, because it sounds like you could be getting insufficient gas to the engine.

If these things don't help, brother, there's always the mysterious, computer-related problem to consider, which could be the case here. If so, you'll have to take her into the shop, but let's hope it doesn't come to that.

Computer failures can be pricey -- and a lot less satisfying to fix compared with the real nuts and bolts stuff.

Tip of the Week:

Notice a sulfurous, "rotten egg" smell from your exhaust in the morning?

That's normal for the rich fuel condition in a cold engine, but if it doesn't go away after warming up, get the engine checked.

Unburnt fuel in your exhaust system can easily destroy a catalytic converter.

Buffalo Jim, owner of Allstate Auto & Marine Repair in Las Vegas, writes a weekly column. Send your automotive questions to him at buffalojim@lasvegasniftynickel.com. If Jim picks your question to answer in Nuts & Bolts, you'll also be the proud recipient of a deck of official Buffalo Jim playing cards, presented in a classy, tin box bearing his hairy image.