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1999 Seville STS
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49 Posts
Discussion Starter #1
Hello all,
I just set the engine back in the car, after replacing the TCC solonoid, Harmonic balancer and handle some coolant leakage, and some small more jobs.
The issue is that I have high Idle around 900 rpm. We try to bypass the power steering switch according to the service manual, and saw there is nothing change, looking to the vacuum leakage, spry smoke/gas and there is no sign for the leakage.

I still have the P1860 TCC solonoid code, the electricity guy checked the solonoid and say he can control the solonoid from the PCM harness side but I still have this code.

Is there any thing I can do more? I am stuck with the engine check light on in this car.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,781 Posts
Is your "high RPM" with a hot or cold engine? A cold start should run at 1200 RPM for about 30-40 seconds and then drop down to 900 till it reaches a predetermined temperature (probably something like 90-100 degrees.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,781 Posts
Check for vacuum leaks, dirty TB and/or IAC valve seat, throttle cable routing.
 

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2001 GMC SLT, Malibu LTZ, 99 STS studded with NP
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499 Posts
What year is this on. I have had this happen to me. On the 99 and older I have put the throttle body gasket on backwards causing high idle. Once I couldn't figure out a high idle on a reinstall and I forgot to hook up the brake booster hose
 

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1999 Seville STS
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49 Posts
Discussion Starter #6
JoeTahoe,
I missed your post. My is 1999 seville STS.

Throttle cable runs free, I had no chance to clean TB and IAC, hope to do that soon, but it is strange that it is all began after the engine removed for different jobs. Could it be bad vacuum hose connection? I mean not a leakage that we didn't recognize.
The issue is that the Idle is not stable, when pumping the gas, it can set to different RPM each time.
 

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2002 STS, 2005 CTS 3.6
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413 Posts
Also, be sure to turn and tighten the pintle valve back into the IAC motor as they tend to come loose causing a lot of idle issues. This should cure your problem as it sounds like the same symptoms one of my cars had.
 

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Registered
1999 Seville STS
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49 Posts
Discussion Starter #8
I just talked to the electrician guy, he told me there is no signal coming from the PCM to the IAC... The GM manual direct to PCM problems in that case, don't know what to do.
 

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Registered
1999 Seville STS
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49 Posts
Discussion Starter #9
Also, be sure to turn and tighten the pintle valve back into the IAC motor as they tend to come loose causing a lot of idle issues. This should cure your problem as it sounds like the same symptoms one of my cars had.
Sorry, can you explain what is the "pintle valve"? Is it the black rubber on the top of the IAC?
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,781 Posts
Yes. The tip of the plunger (for lack of another word).

Right side in this picture.

 

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Registered
2002 STS, 2005 CTS 3.6
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413 Posts
That image that Ranger posted is the way the IAC needs to look when re-assembled and ready to reinstall. The back of that little steel collar on the black plunger, which houses the spring, should not have a visible gap to the IAC body, when it's screwed all the way in. If you remove it to clean it and see a gap, it has turned itself out of adjustment and is the likely cause of all your idle problems. Take it apart, clean everything and turn it all the way back in.
 
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