RPM's at warm idle little high after UIM replacement - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-19-2011, 12:20 PM   #1
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Default RPM'* at warm idle little high after UIM replacement

I replaced the UIM on my '99 SLE just after I bought it, and I also removed the throttle body and cleaned it (I first removed the sensors). Everything else seems to be ok, but I believe that the RPMs don't drop to where they should at warm idle. RPMs at warm idle in gear are around 750 RPMs. Sometimes the RPMs will drop a little below that, but the engine then runs a little more rough and the RPMs go back to around 750. The idle seems a little rough at idle in gear also.

There are no error codes, but I'm wondering if maybe there'* a vacuum leak somewhere. I double-checked my work, and all hose connections are tight and connected to the same locations as before the UIM replacement.

Any ideas on what to check?

Thanks.
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Old 05-19-2011, 12:27 PM   #2
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Vacuum leak. Look real close for a vacuum hose, or a gasket that'* leaking. Spray MAF cleaner around and listed for a change in RPM.
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Old 05-19-2011, 12:30 PM   #3
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I'd double check the IAC as well.
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Old 05-19-2011, 12:37 PM   #4
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I would check for the vacumme leaks around the MAFand IAC (idle air control). The O-rings at these seals can get brittle. Talking about O-rings. Did you replace the O-rings on the fuel injectors?
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Old 05-19-2011, 02:25 PM   #5
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Also, check the rubber connectors on the ends of the vacuum lines. Those get brittle fairly quickly.

You may also want to spray some on the EGR tube that'* hiding under the throttle body. Sure, you never touched it, but that tends to be a sore spot on our engines.
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Old 05-19-2011, 04:14 PM   #6
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Yes, I replaced the injector o-rings. I'll take another look at everything as soon as I can (maybe this weekend).

Thanks.
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Old 05-20-2011, 09:30 AM   #7
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The EGR vacumme leak doesn't really react to getting sprayed. You will need to take it off and check for any cracks. The common spot it along the flange that meets up to the LIM.
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Old 05-22-2011, 01:46 AM   #8
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I guess the way this car runs is the way it ran before I replaced the IUM.

I took a close look at everything today, and I didn't find anythng that I did incorrectly when I previously replaced the UIM. But for good measure I replaced the 2 pieces of hose connected to the solenoid that runs to the fuel vapor canister under the air box, I double-checked that the UIM bolts and throttle body nuts were tight, and I removed the IAC valve and the MAF sensor to make double-sure that the o-rings were there (they were) and the 3 throttle body sensors were connected correctly (they were). I didna't touch the EGR or its metal tubes at all when I replaced the UIM, and I didn't touch them today.

Question: Where can I buy the rubber hose coupler that joins the 2 diffferent size vacuum lines going to the front side of the throttle body? I'm guessing that'* a dealer-only part.

I learned something about this car today - my scan tool showed the RPMs varying between 630 and 650 when the RPM gage was showing around 750 RPMs, so the idle RPMs are in the normal range but the gage is off!
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Old 05-22-2011, 09:09 AM   #9
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at the dealer you have to ask for the tube that goes from the throttle body to the purge solenoid because they dont sell the rubber piece by itself anymore. it comes with the hard plastic tube when you order that.
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