Try looking for an intake manifold leak.

Dear Car Talk

Dear Car Talk | Dec 01, 1996

Dear Tom & Ray:

My question concerns a red 1978 Honda Civic with a 1,500 cc engine and a
five-speed transmission. A friend sold me the car in 1991 and it now has
220,000 miles on it. At first glance, I was reluctant to buy it because of
the large amount of surface rust on the hood and roof. But it had a great
stereo. The engine ran terribly below 2,500 rpm, and the exhaust manifold
was coming apart and causing a loud noise while running. It also burned a
quart of oil per week. I just wanted an inexpensive car with great gas
mileage for my trip to work.

For one reason or another, I parked the car in my then-girlfriend's
apartment parking lot and began to work on it. Over the next three weeks, I
spent all of my spare time rebuilding the engine right there in the parking
lot. The week after that, I had it painted. After that, everything was
finished. Even my relationship with that girlfriend. She argued that I just
used her for her parking lot. But I said I was sure I had used her for much
more than that.

Anyway, I am now married and my wife wants to sell the car because it's not
easy to drive and does not idle well when it's hot. I have already rebuilt
the carburetor. Do you have any other ideas on how I could alleviate this
current problem? -- Michael

TOM: Well, the first thing you should do is call your old girlfriend and
ask her if you can use her parking lot!

RAY: Then you can start looking for an intake manifold leak. My guess is
that when the engine heats up, the manifold warps and lets in excess air.

TOM: And that extra air "leans out" the mixture (i.e., lets in too much air
compared to the amount of gasoline) and makes the car idle poorly. At
higher engine speeds, it doesn't matter as much because you're pulling in
lots of air anyway.

RAY: And here's one more suggestion, Mikey. Once you've fixed the manifold
leak, you might want to sign up for a little interpersonal diplomacy
course. I mean, it could come in handy in this marriage of yours.

TOM: Sign up for one? He should teach one!

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