While searching for vacuum leaks with carb cleaner, there was definitely a leak at the EGR/Intake connection. I replaced that gasket and can not detect any more leaks around the EGR. Fixed a slight pinging issue I had but didn't change the idle or the 335 code. While I had the egr valve off, it seemed to hold vacuum but I cleaned it anyway. I felt good about its operation.

Does this tell you anything? I'll check the sensor and the vacuum lines to it later.

 

The EGR valve can hold a vacuum at the diaphragm but the pintle can be not fully seated which allows exhaust into the intake at idle. That's my point. When you had the EGR valve off did you try to blow through it to see if it was leaking around the pintle?

A diagram for reference



To be honest I do not put much faith in the carb cleaner method to find vacuum leaks on a modern EFI vehicle. Too many lines covered in tubing and other pieces. I find it very unreliable in my experience. I use a small hand held vacuum pump/gauge to test each vacuum circuit. If the circuits test out good then the leak is on the motor someplace.

 

The weather is horrible here so I haven't done anything more...yet.

When I had the EGR valve off I blew through it and it did not seem to allow air through. The EGR circuit also seem good.

So if I understand correctly I have either a vacuum leak or a bad IAC. Could the IAC be the cause of the vacuum leak? This could explain the high idle and 412 code, but would it cause the 172 and 335 code?

I am going to work on searching for vacuum leaks with a vacuum pump, and I will double check all voltages,, especially the rise in voltage with the application of vacuum to the EGR valve.

My suspicion is the EGR sensor and/or the IAC...and maybe another vacuum leak somewhere. Am I on the right track?
I seriously appreciate your guidance. I've learned a lot.

 

Cleared codes and 172 is gone. Drove around and can't get it to return. It's VERY intermittent. Just every few months

I re-ran my tests....the DPFE sensor sits at around 1v, and then climbs to over 3v as I applied vacuum to the EGR valve, and applied throttle, I simply don't see a malfunction with the DPFE sensor, but I'm still getting the KOEO code of 335. Since this is an engine off code, it almost certainly is electrical rather than an issue with the EGR valve itself, yet the sensor and voltage seems to be within range. HOW CAN THIS BE???

After driving for a bit the idle wants to remain at 1k rpms. While running unplugging the IAC has no effect. Restarting the engine also has no effect, as it still wants to idle at 1k rpms. Does this point to IAC??? Can the IAC cause a vacuum leak, which could also lead to the occasional 172 code?

Reset all codes, and KOEO still throws 335, and KOER still throws 412.
I am suspecting an issue with the IAC valve with the elevated idle...I can't find any vacuum leaks and everything I checked checks out fine. Any suggested vacuum leak suspects you can recommend that may be obscure?

And all of this still doesn't explain the code 335 issue. It seems the 335 code and idle issue almost can't be related, right?

The truck runs really good but this thing drives me crazy!

Any thoughts? Suggestions?

Dan

 

As I stated previously you may have the wrong DPFE sensor.


I stated previously the IAC could be bad, hung open or a bad gasket. All of which act as effective vacuum leaks.


Throttlebody gasket, worn throttlebody bore, worn throttlebody actuator shaft, upper to lower intake gasket, lower intake manifold gasket, worn PCV valve grommet, any original vacuum line, bad brake booster, cracked vacuum reservoir on the passenger side inner fender, cracked HVAC reservoir on the blower case, that pesky white vacuum line for the HVAC system to name a few of the most common culprits.


Let's go back to some of the original statements I made. Yes they can be related. It's a process of elimination. To rule out a leaky EGR valve put a plate between the EGR valve and the upper intake. If the high idle is gone you know here to look. If it remains the same then perhaps the EGR is closing all the way, but the new sensor may be the wrong one or it is bad or....I stated before the hoses appear to be the same size, they are not supposed to be. I am not certain how touchy that sensor is to wrong sized hoses, but do know a clogged EGR tube will trigger a code. But we know KOEO the sensor output should be XX value regardless if the hoses are wrong size, plugged EGR tube, etc. That's where I have to rely on info in the PDF file from Tomco. You may have the wrong DPFE sensor. Code 335 may be a rabbit hole, but needs to be validated.



See my responses above.

 

I decided I was over thinking things so I pulled the trigger on a new IAC. Yeah the old was was pretty bad. Fixed the idle thing, idles perfect and the 411, 412 code is gone.

335 and now 336 codes are still there...I'm gonna do the same and just change the DPFE sensor and be done.

Thanks for the help....I learn alot as I run into even small issues so it's worth it.

Dan