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Old 10-01-2012, 11:32 AM   #1
Workerbee
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Default Engine revs at low gear and idle

Help! I have a 2002 SL1 with 120K miles (manual transmission). The engine will rev up and sound "stressed" (inconsistently) in low gears, with idling, and in reverse. Can you give me ideas on what might be causing this?

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Old 10-01-2012, 12:34 PM   #2
BV22
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Default Re: Engine revs at low gear and idle

Next time is revs at idle, if safe to do so, shut the car off and restart it without touching the gas pedal. If the idle returns to normal, the throttle position sensor is suspect. A 1700 rpm intermittent idle speed is the symptom.

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Old 10-01-2012, 01:03 PM   #3
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Default Re: Engine revs at low gear and idle

It can also be a sign that its time for throttle body cleaning, including cleaning the IAC plunger and the seat on the TB it goes into. I've seen cases of both high idle (often idle will come down after 30 seconds or so) as well as initial low idle (idle drops to stop, around 600 RPM, then jumps up to 1000 and then settles) all solved with a good cleaning.
The only reliable way to determine if the issue is a dirty TB/IAC vs a bad TPS is to hook up a computer and read the current "absolute throttle position" percentage that the computer computes. That requires a better than ODBII scanner though. So the easiest solution is to first start with a good TB cleaning. You'll need it either way.

-Robert

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Old 10-01-2012, 01:10 PM   #4
ssewall
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Default Re: Engine revs at low gear and idle

Intake manifold gasket leak, almost universal issue on 00-02 SOHCs.

Spray some carb/intake cleaner around the intake header with the car running (preferably cold; carb cleaner is flammable). If the idle dips, you have this problem.

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Old 10-01-2012, 01:12 PM   #5
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Default Re: Engine revs at low gear and idle

Quote:
Originally Posted by ssewall View Post
Intake manifold gasket leak, almost universal issue on 00-02 SOHCs.

Spray some carb/intake cleaner around the intake header with the car running (preferably cold; carb cleaner is flammable). If the idle dips, you have this problem.
Soapy bubbles provides the same result without the fire risk.

-Robert

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Old 10-01-2012, 02:32 PM   #6
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Default Re: Engine revs at low gear and idle

Though cleaning the throttle plate is a very good idea, spraying the plate with cleaner often 'fixes' the high idle issue because some of the cleaner gets into the TPS, and masks the worn/dirty condition. Often enough the problem comes back in a while.

If you have a scan tool, observe the TPS reading at idle. It should always be 0%. If it is higher, and you have a high idle, then the TPS is at fault.

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Old 10-03-2012, 02:51 PM   #7
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Default Re: Engine revs at low gear and idle

Wow - thanks for the quick responses, which made me pay closer attention to the issue. Now I have more to add: the RPMs increase when I press in the clutch, and when I am at a stop light/signal, I will have to let out the clutch and step on the brake pedal to reduce the RPMs to ease up the engine (and stop freaking out the other drivers). Does that change any answers given?

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Old 10-03-2012, 04:21 PM   #8
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Default Re: Engine revs at low gear and idle

If I understand your post correctly, you are letting the clutch drag against the car held still with the brakes in order to keep the revs down? If so, don't do that for long. Again, find a place where you can stop while the car is idling fast and shut it off. If on restart, the idle is normal, the TPS is very likely shot.

If I misunderstood you, and the act of pushing the brake pedal changes the idle speed, then you have a vacuum issue.

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Old 10-09-2012, 03:11 PM   #9
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Default Re: Engine revs at low gear and idle

You read my second post correctly - I will get it into the shop ASAP. Thanks again for the info!

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