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dewhite

Throttle Relearn

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So, I have been driving around with a MIL for code P0121 for a while (several months) and more recently it's been intermitently causing the Cruise Control not to operate (I think). This is on my 2007 Suburban 1500 w/ the 5.3L, with 110,000 miles which has been running fine and consuming no more fuel than I'm used to...

 

I read up on P0121 and saw that it involves the TPS integrated into my Throttle Body. I decided to clean to TB before spending ~$200 on a replacement.

 

I bought a can of CRC TB Cleaner at the parts store and spent about 45 removing, cleaning the port and paddle and replacing everything per the "remove/replace" instructions on alldatadiy.com I removed maybe .5 to 1mm of sticky carbon sludge from the bottom inside of the port. Is it normal to have this much crap in the top of the engine like this? I looked inside the (i guess it's called) plenum and saw sticky brown stuff all the way back...

 

After checking that the drive-by-wire was functioning with the key in "on" but without starting the engine, I replaced the intake assembly and proceeded with the Throttle Relearn procedure also found on alldatadiy.com Specifically, what I did was:

 

1. Remove negative battery cable for 20 minutes to reset all DTCs.

 

2. Start engine, run in park for 3 minutes

 

-MIL did not come on

-Engine starts at about 1200rpm, then slowly idles down to 800 rpm and back up to a steady 1000rpm

 

3. Remove key for 60 seconds

 

4. Start engine, run in park for 3 minutes

 

-Engine starts at 2000rpm, rises to 2500rpm, and oscillates between 2500rpm and 3000rpm

 

5. A few more cycles of 3. and 4. with the same results.

 

Is there anything else I can try before I have to pony up the cash to have a dealer hookup a tech II and perform a calibration?

 

THANKS IN ADVANCE for any ideas, suggestions, references, questions, etc!

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I'd just take it for a drive and see what happens. Get some air/fuel moving through it.

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Removing the battery cable to clear codes causes the PCM to relearn fuel & timing tables. A perfect reason for not resetting the PCM. A 50-100 mile learning process is in order.

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I would look to see if you got some of the sticky gunk where it does not need to be. Clogging a port or holding open the butterfly?

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It sounds like you have an air leak, go back and recheck the following:

1. check that the throttle body is reinstalled correctly and that the gasket appears to be resealed well to the intake manifold (as you called, "plenum").

2. check and recheck all connection of the intake tube - any leak of unmetered air will cause funny idle issues, the Mass Air Flow meter, located near the filter is what measures the air coming in to the engine.

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the gunk in your in your intake is from oil coming in through the PVC valve. best thing to do is run some Sea Foam through your intake. they have a new spray can with a nozzle that you put in through the TB and you spray down the inside. the nozzle is about 30" long. just follow the directions. if you keep getting a lot of oil in your intake you may want to look into installing a catch can in your PVC line..

 

good luck..

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I just wanted to check back in, and say THANKS!

 

I rolled the truck out of the driveway and dropped it into gear at 2,500 RPM. Driving around for about 10 miles that night made an immediate improvement, lowering the idle in park to a much more managable 1,200 RPM. While driving, the idle was pretty normal, although downshifts came with a noticable surge, especially the 2-1 when coming to a complete stop.

 

Behavior continued to improve over the next several days, and after about 500 miles of driving has returned to what I would consider normal. It still takes about 60 seconds for the engine to settle down to around 600 RPM when I start it up, but that's probably just something I hadn't noticed before I started all this...

 

About the sludge in the engine - did you mean the PCV Valve? What would cause that much oil to creep up through the PCV valve? I remember that replacing that valve used to be a regular maintenance item, and that it was a cheap part and easy installation on my 2000 Silverado...

 

I've also noticed that the Cruise Control is still not working correctly all the time. It often will set and work as expected for as long as I'll use it (in excess of 100 mile stretches this weekend), but if I tap the brake, it may or may not work the next time I try to set it. Once it stops functioning it usually won't set for quite while, or until the truck has been shutdown and started again.

 

I figured that the Cruise Control was a direct result of the TPS reading out of range, but after 500 miles, the DTC still hasn't set itself again.

 

Anybody got any ideas? Again THANKS!

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