Don’t stall on fix­ing leaky valve prob­lem

The Maui News - - AUTO - By Ray Magliozzi

Dear Car Talk:

My 1998 Lexus ES300 has only about 65,000 miles on it. I in­her­ited it from my el­derly dad a few years ago. It has never had any ma­jor en­gine prob­lems. But start­ing about a year ago, it oc­ca­sion­ally stalls right af­ter I start it, be­fore I put it in gear. When this hap­pens, it restarts eas­ily and runs smoothly as long as I give it a lit­tle gas, but as soon as I take my foot off the ac­cel­er­a­tor, the tachome­ter drops to zero and it stalls. I can drive it, as long as I keep the gas pedal slightly de­pressed all the time, even when I’m brak­ing or stop­ping. Af­ter a short time, the prob­lem cor­rects it­self, and it might not hap­pen again for months. I am as­sum­ing that some­thing like a gov­er­nor is stick­ing. Do you know what it is? Is this likely to hap­pen when I am al­ready driv­ing (it never has yet)? Is it go­ing to be dif­fi­cult to di­ag­nose, since it is very in­ter­mit­tent? And how ex­pen­sive is it go­ing to be to fix? — Bruce

I don’t think it’s a gov­er­nor, Bruce. It might be the lieu­tenant gov­er­nor. More likely, it’s a lazy or dirty idle air con­trol valve.

Back in the pre­his­toric days, when car en­gines had some­thing called “car­bu­re­tors,” they also had de­vices called “chokes.” Chokes were me­chan­i­cal flaps that choked off the air sup­ply when the en­gine was cold, so that the fuel-air mix­ture con­tained ex­tra fuel. That kept the en­gine from stalling un­til it warmed up.

Now every­thing is fuel-in­jected, com­put­er­ized and con­trolled by elec­tronic sen­sors. And the choke has been re­placed by some­thing called an “idle air con­trol valve.”

When the en­gine is cold, the IAC sends air past the air-flow sen­sor, fool­ing the com­puter into think­ing you have your foot on the gas. So the com­puter sends in more fuel. But if your IAC is dirty, stick­ing or bro­ken, the cold en­gine won’t get the ex­tra fuel it needs, and the car will stall ... un­til it warms up. Once it’s warmed up, the IAC is no longer needed, so the car runs fine.

So, to an­swer your ques­tions, it won’t hap­pen when you’re “al­ready driv­ing,” be­cause the IAC is rel­e­vant only when you’re idling and the en­gine is cold. Once the en­gine is warmed up, it won’t hap­pen even if you do stop and idle again.

Will it be dif­fi­cult to di­ag­nose? Well, since I di­ag­nosed it, Bruce, how hard could it be?

I’d start by ask­ing your me­chanic to put his scan tool on your car. If a code was stored, that could con­firm that the IAC is at fault. But even if there’s no code, have your me­chanic start by clean­ing the IAC. That may cost you $150 or so.

If that doesn’t fix it, and you need a brand-new IAC, that could be a few hun­dred bucks more.

And you shouldn’t wait an­other year to fix it, Bruce. If you pull out from the curb and the car stalls on you when you’re half­way out into the street in front of an on­com­ing Waste Man­age­ment truck, the con­se­quences could be se­ri­ous.

***

Got a ques­tion about cars? Write to Ray at Car Talk in care of King Fea­tures, 628 Vir­ginia Drive, Or­lando, FL 32803, or email by vis­it­ing the Car Talk web­site at www.cartalk.com.

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