Closer_2001

iTrader: (6)

Vehicle is an 03 RCSB GMC Sierra with the 4.8.

Just bought it, 134k miles.

The throttle body was very dirty and causing the classic rough idle - 500 or so. Cleaned it out with Intake cleaner using a soft toothbrush. Immediately started and ran perfect, idle at about 600-650.

As the truck drives however, it tends to let the RPM hang at about 1500 until you come to a stop, then it will hover around 1000, then settle down. It will also hunt at idle, dropping down to 500 then surging back to 1100.

I've removed, checked, tightened and sprayed more cleaner down the idle passage. It seems the idle motor may not be working correctly? I also swapped the MAF - no changes.

Any thoughts?? Thanks.

PitchblackC3

iTrader: (3)

Take the intake tube off, key on without starting the engine. Watch the action of the blade as someone works the throttle pedal for you. Any hanging should be seen easily.

Closer_2001

iTrader: (6)

I tried this with the engine running, but not without it running. good call.

Running, it tries to correct itself repeatedly, cracking the throttle.

PitchblackC3

iTrader: (3)

What did you find?

Closer_2001

iTrader: (6)

Plugged in HP Tuners...

I can see the TPS going 4-8% on its own.

I commanded Open Loop - Idle goes right to set speed.

Next, commanded IAC to raise idle, lower idle. Idle responds.

Conclusion...computer is telling throttle to adjust for some reason.

Googled and found many threads talking about needing to reset idle with Tech 2 after major TB cleaning. Disconnected Batt for 30 min. Return to idle - while cooler temps than last few weeks - - seems much faster.

If it seems to not have full impact, will go see a good friend who is Service Manager at a Chev dealer to give full relearn with T2.

Closer_2001

iTrader: (6)

OT - Is the TBSS manifold an upgrade over the LQ9 ?