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Old 04-18-2021, 10:07 PM   #1
dntone1491
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Default High idle. Help!

Ok everyone. Iíve read different things on here and other places but Iím still unable to fix my high idle issue.
I have 02 SL (SOHO). I have replaced the Idle control value, throttle position sensor, cleaned the throttle body and replaced the gasket, intake manifold gasket and it still has a high idle around 1200-1500. If I turn the car off then back in then itís fine till I start moving again. I am going to replace the TPS again just to see if that is the issue.
Does anyone else have an idea?
Thank you.
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Old 04-18-2021, 11:44 PM   #2
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Default Re: High idle. Help!

Have you been using live-data at all? That can help you avoid all this parts-changing.

When it is idling too high, block off the IAC port in the TB to see if that brings the idle down or even kills the engine. If that has little effect, then block off the hose to the brake booster; best to plug/cap the port for that on the intake manifold. If the high idle cannot be brought down by blocking either the IAC or brake booster, then slowly slide a block of wood across the TB opening and see if that can kill the engine. Still no joy? Then there has to be a vacuum leak in the manifold itself or a gasket (TB, intake manifold, or EGR valve are all possibilities).

If the engine is idling too fast, it has to be getting more air than intended; the first step is to identify which path that air is getting through.
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Old 04-20-2021, 01:24 PM   #3
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Default Re: High idle. Help!

Quote:
Originally Posted by dntone1491 View Post
If I turn the car off then back in then it’s fine till I start moving again.
classic TPS issue symptom

Quote:
I am going to replace the TPS again just to see if that is the issue.
Bingo, replace the TPS again. Hopefully under warranty.

I had a similar issue. Replaced the throttle body with a spare throttle body I had laying around (IAC and TPS included).

That also had a bad TPS. Replaced that one with a new TPS from Rockauto. Problem persisted, got another TPS under warranty, and that one fixed the high idle.

That's 3 bad TPSs, one of them brand new, out of the box
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Old 04-20-2021, 02:10 PM   #4
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Default Re: High idle. Help!

Get a GM throttle position sensor. Reinstall the old IAC. After market sensors and controls will cause you endless headache.


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Old 04-20-2021, 04:32 PM   #5
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Default Re: High idle. Help!

Quote:
Originally Posted by billr View Post
Have you been using live-data at all? That can help you avoid all this parts-changing.

When it is idling too high, block off the IAC port in the TB to see if that brings the idle down or even kills the engine. If that has little effect, then block off the hose to the brake booster; best to plug/cap the port for that on the intake manifold. If the high idle cannot be brought down by blocking either the IAC or brake booster, then slowly slide a block of wood across the TB opening and see if that can kill the engine. Still no joy? Then there has to be a vacuum leak in the manifold itself or a gasket (TB, intake manifold, or EGR valve are all possibilities).

If the engine is idling too fast, it has to be getting more air than intended; the first step is to identify which path that air is getting through.
I slide a block in front of the TB. The car died. Is that good or bad?
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Old 04-20-2021, 07:26 PM   #6
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Default Re: High idle. Help!

That is good, that is what it should do if there is not a significant vacuum leak raising the idle up. (Like in the brake booster or intake manifold)
As pointed out by others, this is likely to be a bad TP sensor. Either use live-data to verify that, or throw some more TP sensors at it. After a while, you will either get a good sensor that fixes it, or the sheer number of sensors tried, without success, will make it unlikely that the TP sensor was actually the problem.

Did you try plugging the IAC port in the TB? That is real easy to do, and if that reduces the idle then that is another clue that the IAC is not being commanded to "idle" because the TP sensor is bad.
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Old 04-20-2021, 11:58 PM   #7
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Default Re: High idle. Help!

Another less common cause Iíve seen is the connector pins at the pcm for the TB. If you keep having TB issues and youíve tried the OEM tb and the connector it could be the pcm connector. Back probing it may bend the pins enough to resolve it.
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