December 16, 2004

7:22 AM

CarFilter: My wife's old Toyota (1996 Tercell) is having an odd problem. I know very little about engines, and Google has turned up a variety of possible answers [mi]
posted by sixdifferentways to (16 comments total)

Although the car is old with about 100K miles, we have kept it maintained. The battery, filters, hoses, alternator are all fairly new.

The problem is when she puts the car in park or neutral (automatic transmission), the engine revs us really high. There's no meter, but I would guess 1600-2000 RPM. It idles fine in Drive, and it seems to drive fine with the exception of a slight delay in the engine slowing down when the car does (such as coming to a stop - it seems to lag about a second.)

I was afraid the transmission may be going, but I've read it could be the throttle switch, something in the computer controller, a stopped up fuel filter, fuel pump, or stopped up cat converter.

Of course were going to bring it in to the shop, but neither of us has time today. I was wondering what the easiest/cheapest things to check would be first, because I'm afraid their going to want to replace the transmission or say it's something like the "timing belt" (which it's not, as far as I can determine.)
posted by sixdifferentways at 7:29 AM on December 16, 2004

Does the car idle high when you first start it up, or is it just when you shift back into park from drive?
posted by Civil_Disobedient at 8:11 AM on December 16, 2004

The cheapest quickest thing would be to disconnect the battery for 30 seconds or so. This will reset any learned behavior in the computer. Then take a 15 minute drive with some stop and go and some highway speed sections. Your car may drive totally horrible during this learning period.

Disclaimer: The only computer controlled automatics I have experience with are dodges.

I doubt this is a cat, transmission or engine mechanical problem. Sounds like either a bad sensor or a portion of the idle air control circuit is bad/worn. On many vehicles I'd be checking the TPS or IAC but I'm not familiar with late model Toyotas.
posted by Mitheral at 8:17 AM on December 16, 2004

Does the car idle high when you first start it up, or is it just when you shift back into park from drive?

The later - it seems to start up just fine, it's only when she parks and puts it back into park
posted by sixdifferentways at 8:24 AM on December 16, 2004

The cheapest quickest thing would be to disconnect the battery for 30 seconds or so. This will reset any learned behavior in the computer.

Theres an idea - she did have the battery replaced about a week ago. But since this just started yesterday, I didn't think about a connection.
posted by sixdifferentways at 8:26 AM on December 16, 2004

I'm just hoping it's not the transmission. I did some more digging and came up with a few more suggestions:

- The TPS Throttle position sensor) could be dirty or even missing (apparently they can fall off sometimes)

- "the diaphram in the rev limiter"

- the ISC (idle speed controller) is bad

- a major tune-up including spark plugs, plug wires, distributor cap, rotor, fuel filter and air filter. Also, perform a fuel pump pressure test. Clean fuel injection system including throttle bore, idle speed control motor and passages

All of these sound a bit easier to swallow than the transmission going out. If that's the case, I think it would cost more than the car is worth!
posted by sixdifferentways at 8:31 AM on December 16, 2004

it seems to start up just fine, it's only when she parks and puts it back into park

Sounds like either an ECU problem, or a transmission problem. You can try Mitheral's suggestion and pray it's the computer, but I have a bad feeling it's transmission-related.
posted by Civil_Disobedient at 8:36 AM on December 16, 2004

This is likely way too obvious to be the solution, but it could be related -- your car has a fast idle mode that kicks in on cold days. Does the revving problem happen all the time, or just when the engine is cold? Does your temp gauge look normal?
posted by naomi at 8:41 AM on December 16, 2004

This is likely way too obvious to be the solution, but it could be related -- your car has a fast idle mode that kicks in on cold days. Does the revving problem happen all the time, or just when the engine is cold? Does your temp gauge look normal?

The temp gauge reads normal. You may be onto something! I was ignorant of the fast idle mode - and it's been sort of cold here lately. I just took it out for a drive around a few blocks. Starting up cold, it seemed to run overly-fast in park and neutral, but after the engine warmed up a bit, it's a lot better. It still seems to jump from maybe 800 RPM in drive to 1200 or so in park and neutral, which isn't as terrible-sounding. It could possibly just be an adjustment to this fast idle mode that kicks in during cold weather is needed.
posted by sixdifferentways at 9:16 AM on December 16, 2004

Also - since the battery was replaced about a week ago, is it possible the computer just needs to "re-learn" how to adjust the cold weather throttle? "Cold" in Dallas is 40 degrees F or so, perhaps the default is set for a colder climate.
posted by sixdifferentways at 9:19 AM on December 16, 2004

Awesome, I hope that is the explanation! My husband's truck has a fast idle mode in cold weather, much higher than my car, and it freaked me out the first time.
posted by naomi at 10:47 AM on December 16, 2004

1996 is OLD? We've got a 1981 Tercel that still runs great.
posted by trbrts at 10:58 AM on December 16, 2004

1996 is OLD? We've got a 1981 Tercel that still runs great.

I've got a '78 Cressida that actually has a fast idle problem that sounds a lot like this. I always figured it was because the damned thing was 26 years old.
posted by jessamyn at 11:33 AM on December 16, 2004

I don't know Toyotas well, but it could be a bad Park/Neutral switch (or the wire to it from the ECM). It takes more air to idle in drive than in park or neutral (higher engine load), so if the ECM didn't know that you had shifted into neutral, it wouldn't reduce the idle air.
posted by rfs at 12:35 PM on December 16, 2004

Well, the warmer weather, driving on the highway, or something seems to have indeed "fixed" it for now. A tune-up of some of these other things would probably be a good idea at some point.
I guess '96 isn't that old mechanically, it's just not the best looking ride in the neighbourhood.
posted by sixdifferentways at 1:38 PM on December 16, 2004

That could indicate a loose connector or terminal pin - it may come back. If it does, and you want to test my theory, after you go back to park/neutral wait and see if the RPM flare goes away - this would be the idle system learning the load change. When RPM is back to normal, shift back to drive - you should get a big RPM sag, maybe even a stall. If it doesn't do this, it's something else. Good luck !
posted by rfs at 8:21 PM on December 16, 2004