Hummer H3 For the Hummer driver who wants the rugged look and off road capabilities of the Hummer, but in a smaller size and with a more fuel economy friendly engine.

h3 3.7 rough idle no codes

Old 02-06-2019, 05:16 PM
Junior Member
Thread Starter
Join Date: Feb 2013
Posts: 5
Default h3 3.7 rough idle no codes

going nuts!!! ive seen so many h3 with identicle issue but no fix. iv e cleaned TB ,mass sensor,new aur filter,plugs.
idle drops to 500-600rpm. runs great other than that. if iraise the idle to 700+ smoothes out. NO CODES.pvc tube clear.
dont know if the TPS would throw a code,dont know if IAC motor would throw a code. i do know that if either of these sre malfunctioning that the entire TB has to be replaced.
I spoke to a tech at Cardone industries. he said could be a multitude of things. maybe but fuel,air, spark are what ive checked so far. nothing obviuos.
the tech told me that i need a mechanic to scan my engine and their scan device is much more than code reading.
any body know what this may be? with 1000s of people having the same issue i hope one of you guys can help.
Old 02-08-2019, 10:32 AM
Doc Olds's Avatar
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Join Date: Jul 2007
Location: Boat Town USA MI
Posts: 8,662

Welcome to HF. MOVED from the wrong General Hummer Talk section.

Appears from your other posts you have seen this FAQ: Acts like it wants to stall/rough idle -No CEL -What To Do:

When you ask a question, year, model and miles are important. How long have you had this truck?

When you cleaned the TB, did you remove it and use TB Cleaner?

You do understand that I5 engines are not inherently balanced, have a separate balance shaft to reduce vibrations of the first, second and third order. Means when you speed up RPM to 700+ it seams to go away because the second & third order vibrations are lower. Normal.

Also be aware the H3s are equipped with fuel saving technology that reduces RPM when coming to a stop under no load, the PCM actually calculates how low to idle based upon the electrical demands from all accessories operating and targets that position so as to keep the alternator running just fast enough to offset the current power demand. If the PCM targets 500-600 RPM, then you feel the vibrations more. Normal.
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