Another rough idle and new codes...

[05YukonXL]

All this leads to P0171, P0174, P0300, P0305...

Background: Have had intermittent P0305 (not AFM cylinder) for 18 months on 2014 LT with 115000 miles but there were no clear cause or noticeable symptoms other than minor bad idle at low rpms (while stopped). Coil good, spark plug good, took off valve cover and everything appeared ok there too, clean oil on every oil change). Very drivable and barely noticable.

Jump to this past December on a cold morning in NC the the truck struggled to turn over with traction, stabilitrac, abs, airbag warnings). Very rough idle at low RPM (almost stalling). Drove home the 300 miles to warmer climates.

Got home. Replaced battery (was not holding charge). Didn't really have the bad symptom again... other than intermittent rough idle at low RPMs. Still not settled, took the truck to mechanic to check and replace spark plugs, replace coil, did a 'tune up', cleaning throttle body.

Next day, same intermittent codes P0305 and occasionally P0300 now with a very high idle... 1800-2200 rpms. Let off the brakes and truck would get to 35-40mph and 4th gear on its own, and maintain speed! When slowing (on the brakes) every downshift was met with acceleration! Drove like this for a month thinking it needed to recalibrate to recent work.

To no avail, returned to mechanic he said 'ECM is commanding idle at 1800 - take it to the dealer'. Dealer did a reset/relearn but was not able to identify specific cause. But no more high idle!

However the rough idle from before is back... intermittent P0305/P0300. And THEN on a cooler morning this weekend a repeat of December. Truck barely turned over.. nearly stalled ... codes now are: P0171, P0174, P0300, P0305. Running Lean both banks and misfires...

I'm thinking time for vacuum leak test, check/replace driver side valve cover/gasket, maybe intake manifold gasket, MAF sensor, Fuel injector regulator, 02 sensors... is there an order I should be checking.

Am I missing something obvious? What say you ??

Since my mechanic through up his hands I'll take it to another shop or the GMC dealer.

 

[swathdiver]

All this leads to P0171, P0174, P0300, P0305...

Background: Have had intermittent P0305 (not AFM cylinder) for 18 months on 2014 LT with 115000 miles but there were no clear cause or noticeable symptoms other than minor bad idle at low rpms (while stopped). Coil good, spark plug good, took off valve cover and everything appeared ok there too, clean oil on every oil change). Very drivable and barely noticable.

Jump to this past December on a cold morning in NC the the truck struggled to turn over with traction, stabilitrac, abs, airbag warnings). Very rough idle at low RPM (almost stalling). Drove home the 300 miles to warmer climates.

Got home. Replaced battery (was not holding charge). Didn't really have the bad symptom again... other than intermittent rough idle at low RPMs. Still not settled, took the truck to mechanic to check and replace spark plugs, replace coil, did a 'tune up', cleaning throttle body.

Next day, same intermittent codes P0305 and occasionally P0300 now with a very high idle... 1800-2200 rpms. Let off the brakes and truck would get to 35-40mph and 4th gear on its own, and maintain speed! When slowing (on the brakes) every downshift was met with acceleration! Drove like this for a month thinking it needed to recalibrate to recent work.

To no avail, returned to mechanic he said 'ECM is commanding idle at 1800 - take it to the dealer'. Dealer did a reset/relearn but was not able to identify specific cause. But no more high idle!

However the rough idle from before is back... intermittent P0305/P0300. And THEN on a cooler morning this weekend a repeat of December. Truck barely turned over.. nearly stalled ... codes now are: P0171, P0174, P0300, P0305. Running Lean both banks and misfires...

I'm thinking time for vacuum leak test, check/replace driver side valve cover/gasket, maybe intake manifold gasket, MAF sensor, Fuel injector regulator, 02 sensors... is there an order I should be checking.

Am I missing something obvious? What say you ??

Since my mechanic through up his hands I'll take it to another shop or the GMC dealer.

Can you run a misfire graph or see misfires on cylinder 5? How about a compression test?

What are your Long Term Fuel Trims once warmed up on both banks?

What work if any was done in the months leading up to these codes being set? What brand of parts were used?

 

[steiny93]

Your getting lean and random misfire codes.

Start with the basics
- what does live data show?
- what is the fuel pressure at the rail?
- test for an intake leak (spray some starting fluid or brake clean around the top of the engine, but away from the air cleaner, and see if it rev's up)

I'm thinking either fuel pressure or intake leak (it'll be something affecting all the cyclinders)

 

[Fless]

If it's a Flex Fuel engine and you're not running E85, check the alcohol content of the fuel with a scanner. Reset if necessary.

 

[05YukonXL]

Thanks everyone... I'll have to record some data (no graphs) with my basic scanner - just did starting fluid around the top of motor (and 'usual suspect' areas) made no difference... will report back.

 

[05YukonXL]

If it's a Flex Fuel engine and you're not running E85, check the alcohol content of the fuel with a scanner. Reset if necessary.

Is Flex Fuel. Previously (last dealer visit) when the idle was commanding at 1800 rpms the ECM was reading 77% Ethanol in the fuel .. fuel in the tank was shown to only be 3% ethanol via testing fuel sample, dealer reset/relearn on that.

 

[swathdiver]

Not Flex Fuel. Previously (last dealer visit) when the idle was commanding at 1800 rpms the ECM was reading 77% Ethanol in the fuel .. fuel in the tank was shown to only be 3% ethanol via testing fuel sample, dealer reset/relearn on that.

Yes it is if it's a 2014. The LMG and LC9 are Flex Fuel engines. Supposed to have a yellow gas cap.

 

[05YukonXL]

Yes it is if it's a 2014. The LMG and LC9 are Flex Fuel engines. Supposed to have a yellow gas cap.

Your right, yellow cap!

 

[05YukonXL]

Couple notes and responses:
No major work prior 18 months other what is mentioned. The vehicle had new radiator and AC condenser installed 18 months ago and it sat for a few months waiting for said parts.

P0305 does not show up under PENDING while other three codes ARE PENDING.

FRP(psi) ratings at cold, idle, revving, warm between 43.4 idle and 57.9 revving

MAP(psi) 5.5 idle, 3.8 revving, later 4.6 revving and 5.5 idle

Baro(psi) consistent at 14.9 ( 14' above sea level, 1/2 mile from intercoastal) which is what the airport is currently reporting - so that is accurate.

ALCH_PCT(%) consistent at 3.1 (is that ethanol reading?)

When revving (pushing accelerator) the motor stutters as it's grasping with command ... it holds RPMs okay, just to and from it hiccups.

Data: I need to do a longer idle and recapture more fuel trim data but here's what I nabbed so far from elcheap scanner. Manually recorded data from scan tool and pasted below. First column vehicle "Off". Next column readings right at cold start. Third column revved engine and took readings at 1700rpm. Fourth column readings once back to idle. Fifth column, did a second high 'Rev 2' 1600 rpm and took readings, Sixth Column let engine go back to idle for readings. Last two colums: took readings again a few minutes later at idle.

	OFF	Cold Start Idle	REV 1 HIGH IDLE	Back to IDLE	REV 2 HIGH IDLE	Back to IDLE	LONG IDLE	Even longer Idle
DTC_CNT	1​	1​	1​	3​	3​	3​	3​	3​
FuelSYS1	—	CL	CL	OL-FAULT	OL-FAULT	CL	CL	CL
FuelSYS2	—	CL	CL	OL-FAULT	OL-FAULT	CL	CL	CL
LOAD_PCT(%)	0.0​	22.0​	13.7​	14.5​	13.7​	12.5​	12.5​	12.2​
ECT(ºF)	109​	109​	122​	152​	156​	163​	163​	163​
SHRTFT1(%)	0.0​	6.3​	22.7​	0.0​	0.0​	-5.5​	7.8​	3.1​
LONGFT1(%)	25.8​	25​	29.7​	29.7​	29.7​	29.7​	29.7​	29.7​
SHRTFT2(%)	0.0​	20.3​	15.6​	0.0​	0.0​	0.0​	10.9​	11.7​
LONGFT2(%)	29.7​	29.7​	29.7​	29.7​	29.7​	29.7​	29.7​	29.7​
FRP(psi)	57.0​	43.5​	43.5​	57.9​	57.9​	57.4​	43.9​	43.1​
MAP(psi)	14.9​	5.5​	3.8​	5.7​	4.6​	5.8​	5.2​	5.4​
RPM(rpm)	0​	664​	1700​	606​	1600​	641​	608​	610​
SparkADV(º)	8.5​	11.5​	41​	19.5​	41.5​	7.5​	15.5​	14.5​

Next data digs deeper into first three columns but again, I need to capture more fuel trim data over longer (warmer engine) period.

	OFF	Cold Idle	REV HIGH IDLE
DTC_CNT	1​	1​	1​
FuelSYS1	—	CL	CL
FuelSYS2	—	CL	CL
LOAD_PCT(%)	0.0​	22.0​	13.7​
ECT(ºF)	109​	109​	122​
SHRTFT1(%)	0.0​	6.3​	22.7​
LONGFT1(%)	25.8​	25​	29.7​
SHRTFT2(%)	0.0​	20.3​	15.6​
LONGFT2(%)	29.7​	29.7​	29.7​
FRP(psi)	57.0​	43.5​	43.5​
MAP(psi)	14.9​	5.5​	3.8​
RPM(rpm)	0​	664​	1700​
VSS(mph)	0​	0​	0​
SparkADV(º)	8.5​	11.5​	41​
IAT(ºF)	86​	78​	77​
MAF(lb/s)	0​	0.01​	0.02​
TP(%)	30.6​	17.6​	23.1​
O2B1S1(V)	0.445​	0.115​	0.705​
SHRTFTB1S(%)	0.0​	27.3​	4.7​
O2B1S2(V)	0.450​	0.090​	0.710​
SHRTFTB1S2(%)	N/A	N/A	N/A
O2B2S1(V)	0.445​	0.090​	0.750​
SHRTFTB2S1(%)	0.0​	29.7​	10.9​
O2B2S2(V)	0.445​	0.055​	0.720​
SHRTFTB2S2(%)	99.2​	99.2​	99.2​
EVAP_PC(%)	0.0​	0.0​	14.1​
FLI(%)	36.5​	36.5​	365​
WARM_UPS	2​	2​	2​
CLR_DIST(miles)	0​	0​	0​
EVAP_VP(inH20)	0.018​	0.030​	-0.189​
BARO(psi)	14.9​	14.9​	14.9​
CATEMP11(ºF)	32​	746​	951​
CATEMP21(ºF)	32​	746​	951​
VPWR(V)	12.202​	13.3​	14.617​
LOAD_ABS(%)	0.0​	0.999​	0.999​
TP_R(%)	16.9​	3.1​	3.5​
AAT(ºF)	75​	75​	75​
TP_B(%)	29.8​	16.1​	21.6​
AAP_D(%)	18.8​	18.8​	22.7​
AAP_E(%)	9.4​	9.4​	11​
TAC_PCT(%)	17.6​	4.7​	12.5​
ALCH_PCT(%)	3.1​	3.1​	3.1​

If only I knew how to interpret all this data!

 

[Fless]

If you can, change the MAF setting to g/sec.