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My wife has an ' Corvette with an engine that's...

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Dear Tom and Ray:



My wife has an '85 Corvette with an engine that's racing. For about a year now,
whenever she stops at a light it's been racing at between 1,100 rpm and 1,300
rpm. If she taps the accelerator pedal, it drops to 850 rpm. I took it to a
mechanic who said it was some type of air sensor valve, which he proceeded to
replace. The problem continued. He then said it was the throttle body, which he
also replaced. It still raced. Then, last week, he said it was the throttle
cable, which he replaced. Now it's racing at 1,600 rpm! My wife is looking at me
like I'm a chump, and I think I'm starting to agree with her. Before I take out a
second mortgage to pay for more repairs (the throttle body was $500!), can you
give me some suggestions on how to proceed? -- Jim

TOM: I'm going to start by suggesting you proceed to another mechanic, Jim. All
of these things are reasonable guesses, but the fact that he guessed the cable
LAST tells me that he's not approaching this very scientifically.

RAY: The FIRST thing to do is to eliminate the cable from the equation, since --
as you now know -- it's a whole lot cheaper than a new throttle body. So you
disconnect the throttle cable at the throttle body and see if the engine still
races. If it does -- with the cable disconnected -- then you know the problem is
in the engine compartment.

TOM: And once you narrow it down that far, then again, I'd start by eliminating
the simple stuff first. Rather than replace the air control valve and the entire
throttle body, I'd check the throttle return spring. On a 15-year-old car, the
return spring that closes the throttle could simply be weak and worn out. And
that could account for an intermittent fast idle.

RAY: And if the spring ends up fixing it, you're going to be awfully miffed at
this mechanic. Why? Because the spring costs about 95 cents.

TOM: That may not be it. But I'd certainly eliminate that possibility before I
spent any more money on parts. Good luck, Jim.
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