CARTALK\Early Japanese emissions systems 'choke' some life out of engine.

Byline: Tom & Ray Magliozzi 

Dear Tom and Ray: I read in one of your recent columns that you shouldn't race the engine when you first start up (vrrroooom!) because it causes excess wear on a cold engine. This has always been my understanding as well. But several Japanese cars I've owned, including a Datsun B210 and my current Toyota Tercel, have their automatic chokes set so that the engine does exactly that. It races extremely fast, especially on a cold day when the choke is on full.

Several friends say their Japanese cars do the same thing. This is not just a fast idle, the engines really rev. I read in the manual that the Tercel is set correctly when it runs at 2,500 to 3,000 rpm at full choke. In spite of this terrible behavior, these cars seem to run for well over 100,000 miles. In fact, in the Northeast where I live, the bodies rot out before the engines go.

So what's going on here? How can these manufacturers set their idle speeds so high against conventional wisdom and get away without damaging their cars?

- Gary

Ray: Well, Gary, the reason the engines revs so high is because of the emissions equipment. The cars you're talking about are from the early days of serious emissions systems. And without a very high idle, the cars would experience what is known as "cold engine drivability problems." That's Japanese for "the car stalls until it's warmed up." So they cranked up the cold idle to keep the cars from stalling.

Tom: And that excessively high, cold idle speed did decrease the life of the engine, but at least it kept the car running. And back in those days, that was the primary objective. Getting 200,000 miles out of the engine was a distant second.

Ray: So to answer your question, Gary: How could these manufacturers set the idle speeds so high and not damage the engines? I think the answer is that the engines were made with exceptionally close tolerances (the spaces between moving parts). And despite this high-revving "abuse," they still lasted a heckuva lot longer than most American-made engines of the same era. So their owners never thought to complain about getting "only" 100,000 miles.

Tom: But the "conventional wisdom" still applies. A lot of wear and tear occurs during those first few seconds after the motor starts, before the oil has fully circulated. And we still believe that's the worst time to step on the pedal and rev the engine.

Ray: Well, perhaps it's the second-worst time. The worst time to rev the engine is when the car is in gear, your inspection sticker has just expired, and you're sitting at a stop light behind a state police car.