04 idle issues.

[Walkercraig01]

so my 04 is incredibly nice. runs great, until it doesnt. it has a rly rough idle.. so i unhoked the maf. and it evens out.. cleaned it. plugged back in. goes right back to rough. prev owner said it was replaced and it is a delphi.. also has went to reduced engine power twice. bit if you turn it off and restart it its bnack to normal.. so i cleaned the throttle body ., check the connection. seems ok. i was considering replacing the pcv valve. but with my work schedule its hard to get to it.. so any ideas would be greatful.. it pulls lean codes in bank 2 and 1. but everything fuel related is fine.

 

[OR VietVet]

Throttle body connection "seems fine". Anytime the T/B is replaced GM recommends new harness for a reason. Previous owner replaced MAF, when? Even a quality MAF/Delphi can be defective. Live data scanner and get some readings. PCV valve is an updated valve cover.

 

[justirv]

so my 04 is incredibly nice. runs great, until it doesnt. it has a rly rough idle.. so i unhoked the maf. and it evens out.. cleaned it. plugged back in. goes right back to rough. prev owner said it was replaced and it is a delphi.. also has went to reduced engine power twice. bit if you turn it off and restart it its bnack to normal.. so i cleaned the throttle body ., check the connection. seems ok. i was considering replacing the pcv valve. but with my work schedule its hard to get to it.. so any ideas would be greatful.. it pulls lean codes in bank 2 and 1. but everything fuel related is fine.

Have the intake gaskets ever been replaced? These can shrink and cause inconsistent vacuum leaks. Spray an aerosol of your choice around the edge of the intake to see if it affects idle speed. Mine showed more when cold, as the engine warms, they tend to expand.

 

[Fless]

Good suggestions above. Your PCV "valve" is likely integrated into the driver's side valve cover. Or does it have a physical PCV valve that can be easily replaced?

Put a scanner on it and read the short- and long-term fuel trims. Post them up here. A vacuum leak or a mis-reporting MAF sensor could cause the rough idle, but the only way for us to tell is to get some live data to evaluate. Are all air connections between the air filter and the throttle body tight and sealed? No leaks? Any exhaust leaks?

Post up the MAF value at hot idle; it should be very close to engine displacement in liters (5.3?) in g/sec.

 

[Walkercraig01]

i will ppost some numbers monday, i got the idle to even out.. however misfires on 2 and 1 still and p0300. ive added grounds, ive swapped the maf onto my 05.ive cleaned the throttle body. no changes im going to replace wires and check plugs. coils.. sometimes it goes tor educe power sometimes it just pulls p0300. ive sprayed brake cleaner and cant finds any leaks

 

[Walkercraig01]

plugs on 1 and 2 are looking lean. which it has pulled those codes.. only thing i dont like they are ngk plugs. but look good. when it idles it smells like gas which i assume is due to the misfires.. i should also say when driving down the road., it shows zero misfires. but the times it has went to reduced power i was driving. so im just kind of lost.

 

[Marky Dissod]

Try removing and cleaning the everlovin schidt out of your valvecovers. Pay special attention to the hidden PCV passages.

 

[Fless]

Do a CASE relearn to rule it out; might minimize the misfires.

 

[Walkercraig01]

This is what I got

 

[Walkercraig01]

This was after about a 10 min drive at which I got p1516 reduced power twice . I cleared it and it ran back to normal and could drive normal speeds . That's at idle aswell

 

[Fless]

When the code is present a capable scanner can look at the freeze frame data, if it's there. Capturing that might help you see what's causing it to set. One thing some owners have had to repair is the throttle body harness within a foot of the connection to the TB. The wires underneath the insulation get compromised and typically a new pigtail is installed. @89Suburban did this, I think. YMMV

Check the diagnostic path here, but verify your vehicle info first, then navigate to the correct page:

A L L Diagnostic Trouble Codes ( DTC ) — 2004 Chevrolet Tahoe 2WD V8-5.3L VIN T Service Manual | Operation CHARM

Detailed repair manual for the 2004 Chevrolet Tahoe 2WD V8-5.3L VIN T.

charm.li

Expand the Testing and Inspection link, then the P Code Charts link, then scroll down to P1516 and see the documents underneath that link.

 

[Walkercraig01]

Appreciate it , I have seen a video about that .. I took it for a drive about 90 miles round trip and it only went to reduced once which compared to normal is fantastic . It was missing . But it smooths out and drives perfect when not at idle . So I will peel back the insulation and look into that . Also probably gonna swap some coils around and the normal stuff just to see what happens lol

 

[4Eyedturd]

I’m following because I’ve got the same issue on my 05

 

[Fless]

I’m following because I’ve got the same issue on my 05

Would you describe your issue in more detail?

Any DTCs?
Throttle body been thoroughly cleaned lately?
Rough idle?
With a scanner compare the commanded idle speed with the actual idle speed.

 

[4Eyedturd]

Would you describe your issue in more detail?

Any DTCs?
Throttle body been thoroughly cleaned lately?
Rough idle?
With a scanner compare the commanded idle speed with the actual idle speed.

Just a rough idle but it drives fine. I’ve pulled the plugs to find pretty new looking NGK’s.
Current codes are P0420, P0430, and P0455.
Throttlebody has been thoroughly cleaned.
Not sure what commanded idle is but it idles at mid 550-600rpm.
I put a smoke machine in the intake to find any leaks but I found none.

 

[Fless]

@4Eyedturd Looks like your charging voltage might not be up to the proper level at idle. Something to investigate.

Click on the link below and verify your make and model. Then click on the Testing and Inspection, then click the P Code Charts link. Scroll down to your observed codes and the diagnostic paths are detailed.

A L L Diagnostic Trouble Codes ( DTC ) — 2005 Chevrolet Tahoe 2WD V8-5.3L VIN T Service Manual | Operation CHARM

Detailed repair manual for the 2005 Chevrolet Tahoe 2WD V8-5.3L VIN T.

charm.li

The P0455 might be diagnosed with a "purge and seal" test.
The other two are catalyst efficiency codes and point to a restricted exhaust (plugged cat) or weak or old O2 sensors. Also check for exhaust manifold leaks.

 

[Walkercraig01]

Mine I cleaned the throttle body and it seemed to go away. It still misses and shows misfires but it hasn't gone into reduced power . And driving it doesn't misfire at all. Your 05 is cat codes sure it ?

 

[4Eyedturd]

All 4 O2 sensors seem to be reading, the voltages all bounce around. Not sure what else to test to confirm it’s the cats.

Battery voltage fluctuates I assumed it was normal operation with the factory setup. That pic was at an idle after a 30min drive, could be an under sized battery?

As for the evap code I’ve tried another purge solenoid, cleared the line from the motor to the charcoal canister, replaced the solenoid next to the charcoal can and tried a junkyard charcoal canister. Tried a smoke test as well as a new gas cap. I’ll look into the purge and seal test.

 

[Marky Dissod]

All 4 O2 sensors seem to be reading, the voltages all bounce around.
Not sure what else to test to confirm it’s the cats.

The REAR O2 sensors should NOT 'bounce around'.
If they do not read consistently read UNDER 500mV, the catalytic converter(s) is(/are) not working properly.

 

[4Eyedturd]

The P0455 might be diagnosed with a "purge and seal" test.
The other two are catalyst efficiency codes and point to a restricted exhaust (plugged cat) or weak or old O2 sensors. Also check for exhaust manifold leaks.

Any suggestions for a bi-directional scanner to do this?