2007 Tahoe - code, starting, idle issues

[txss]

Hi all, I have a 2007 Tahoe w/105k. 5.3L. I have made no mods except a K&N air filter.

First issue:
About 5k miles ago I started to get a P0121 code. After researching this, I came to the conclusion to clean the MAF. I did this, it worked for about a week. I cleaned it again, it worked for about 2-3 weeks and then again, several more weeks. Now it seems to go off and on intermitentaly. I thougt maybe the oil from the K&N could be fowling it but it has very little oil on it. It has been off for about a week with no cleaning (Hmmmmm??). I am wondering if anyone has a solution for this? Should I just replace the MAF? Is there something else that could be creating this issue?

Second issue:
Starting has become a big problem. I added some STP High Mileage Fuel System Cleaner to the tank about 2k miles ago and since, the starting takes 5-10 seconds of cranking to start. I have tried different grades of fuel. Another additive, etc.. No real change. Today it started twice within about 4 seconds but most days it's 5+. No changes so I am puzzled. Could it be a bad fuel pump? Could it be ignition sensors? I am not seeing any codes.


Here are my thoughts:

1. Clean the MAF, again
2. Replace spark plugs
3. Clean the A/F
4. Check fuel pressure (not sure how??) - any advice accepted

Any other thoughts? Any others parts I should replace? Anyone else with experience with any of these issues? I am mechanically inclined so I can do most work on my own so your feedback is appreciated!

 

[clkelley]

Welcome to the neighborhood!

When you clean the MAF, make sure to use actual MAF Sensor cleaner. Also, just to rule out the K&N, put a paper filter back in until the issue is resolved, there could be more oil in it than you realize and this is quite common for oiled filters.

That being said, I would try cleaning the throttle body as well. It is not hard to remove at all, but make sure to use actual throttle body cleaner and some blue shop paper towels to get all the gunk out of it, you would be surprised how bad the build up is.

I am betting that will solve your issues. If not, then move onto the other stuff...

 

[txss]

No luck - Help!

Thx CLKelley but that has been done, several times. No change.

P0121 code is back with a vengeance and hard starts.

Latest - I have replaced the MAF, spark plugs and wires, no change. I checked the Fuel Pressure and it slowly comes up to about 48 upon startup. When I punch it, it drops 3-6PSI and then goes back to 48. I don’t know how many PSI it should have but I am thinking 50+. I will have to verify with the book tomorrow.

I dropped by Orielly and they printed a code sheet and it says the "Reported Fixes" are:

• Clean TB (done)
• Clean MAF (done)
• Perform Idle Air Volume Learning Procedure - NOT done
• Perform TB Cleaning Procedure - done, I think!?
• Perform TB Relearn Procedures - Not done
• Program the TCM - Yeah, ok!
• Replace Brake Light Switch - really? Anyone heard of this or know why?
• Replace TB - Not done, would like to avoid
• Replace Fuel Pump
• Replace EVAP Emissions Canister Purge Solenoid/Valve - Not done
• Replace Intake Manifold Gasket - Not done
• Replace PCM - again, yeah right!
• Reset PCM - not sure how without software

If the fuel pressure is ok, I think next on my list is to try the Throttle Body Sensor (not sure if one exists on here but the code claims it). No one can find the part so I wonder if its the TB itself??

Still looking for any assistance/thoughts on this.

 

[clkelley]

Resetting the PCM, you can disconnect the battery for about 20 minutes and then reconnect and see if that helps there. As for the throttle body sensor, it is a part of the fuel pedal assembly, unplug it and check the harness and plug for moisture first, clean and dry it if necessary, then either way add some dielectric grease to the plug to ensure a proper connection. THEN, if that doesn't help, replace it, the entire pedal and sensor comes as an assembly...

 

[clkelley]

Sorry I didn't cover all these...

I dropped by Orielly and they printed a code sheet and it says the "Reported Fixes" are:

• Perform Idle Air Volume Learning Procedure - NOT done Good idea
• Perform TB Cleaning Procedure - done, I think!? Should be done
• Perform TB Relearn Procedures - Not done Shouldn't be necessary but worth a try
• Program the TCM - Yeah, ok! Not sure how that would help...
• Replace Brake Light Switch - really? Anyone heard of this or know why? That is odd indeed
• Replace TB - Not done, would like to avoid It is a simple part, you shouldn't need anew one
• Replace Fuel Pump I doubt that is it
• Replace EVAP Emissions Canister Purge Solenoid/Valve - Not done This shouldn't be the issue on an 07
• Replace Intake Manifold Gasket - Not done Quite possible, these engines are kind of known for the intake gaskets going bad, use carb cleaner while it is running and spray around the intake manifold, if you have a bad gasket it will effect the idle when you spray around it.
• Replace PCM - again, yeah right! Yeah, um, no...lol
• Reset PCM - not sure how without software unplug the battery for a bit to reset it

 

[txss]

Thanks clkelly. I have cleaned all connections one last time related to the MAF, TB and the sensor on the pedal (APP or APS if I'm not mistaken). I used CRC electrical connection cleaner. My TB was nasty once I removed it. Last time I just wiped out what I could and sprayed a can in it so maybe I missed something. I need one more can of cleaner before I'll bolt it back on so its nice and shiny. Here are my next steps:

• Perform Idle Air Volume Learning Procedure
• Finish TB cleaning
• Replace the Fuel Pressure Regulator (if possible)

Fuel pressure came in at 48PSI. I think its on the low side but not by much so I am not sure if I am going to tackle replacing the fuel pump/filter assembly just yet.

Anyone else, feel free to chime in....... THANKS!

 

[txss]

Thought I would post the latest in my saga to eradicate P0121... conducted a VERY thorough cleaning and used the grease as suggested. So far, code gone however the start up issue still exists. I am thinking fuel pump/filter now. I'll tackle that tomorrow.

My new issue is idle. Its all over the place. I tried a Throttle/Idle Learn I found online and it seemed to bring it down and clean up shifting a bit but I am still at 1000-1200RPMs no AC idle. And down shifting is horrible. I found a TSB online and it states to use a Tech 2 to get into the ECM to set the idle etc.. (TSB1 - #PIP4578). Is this something I have to go to a dealer for now? I really want to avoid that. Any thoughts out there? Thanks!

 

[clkelley]

Try disconnecting your battery for about 30 minutes, time enough for all the power to drain out of the system and then reconnect it. After that, if that doesn't work, try using your scanner to clear the codes. Sometimes with those codes, even though the CEL is off, the code will remain in the system, you may try that.

Unfortunately, if that doesn't work you may have to go to the dealer to have the ECM flashed for the idle.

 

[NCFD4303]

that code is for a throttle position sensor. they used to have a recall on some but your out by miles,you have to buy a new throttle body to get the sensor. That will fix both of your issues.