P0171 and P0174 CODES

[MARK JOHNSON]

My issue with my 2003 Tahoe is when the weather gets below 35 the check engine light comes on and throws a PO171 and PO174 code and runs rough at idle.
After the weather warms up past 35-40 the check engine light will turn off and is fine.

This has me very confused, Any other experiencing the same issues?

 

[HiHoeSilver]

My issue with my 2003 Tahoe is when the weather gets below 35 the check engine light comes on and throws a PO171 and PO174 code and runs rough at idle.
After the weather warms up past 35-40 the check engine light will turn off and is fine.

This has me very confused, Any other experiencing the same issues?

Maybe a manifold leak that seals up when warm?

 

[rockola1971]

Maybe a manifold leak that seals up when warm?

Thats exactly what it is. The norm seems to be right around below 35-40deg and the engine will act a fool. Run like crap until warmed up. Throw codes below 35-40deg and in the summer perfectly fine.

 

[MARK JOHNSON]

Thanks for the info, even though its a bit cold outside I will need to take care of it this weekend. At least its suppose to warm up to 11 tomorrow

 

[Merc1973]

I too have these problems with these 2 codes just after a long trip from MD to MI and back in the cold blast of winter. I experienced them after I got back and went through the enclosed touchless car wash. There was a lot of vapor/steam in the air since it was 10 degrees out, it began to idle pretty bad almost like it wanted to stall, I kept the RPMs up until the wash was finished. Idle was back to normal after being in the cold dry air.Its been starting just fine like it always does, even cold weather. Slight rough idle now since CEL came on. Comes back after clearing the codes.


I also noticed that when accelerating lightly when going above 2200-2400 RPM there is a slight hight pitched whistle just as it's about to change gears. It''s always done this. Sounds like the whistle in my 73 Cougar when I had a really bad carburetor gasket leak.


Suggestions? Intake gasket? BTW I have 230,000 miles or so.


I will clean my MAF and try some carb cleaner around the intake gasket....

If it is the intake is the culprit, I found some good info:

http://www.tahoeyukonforum.com/threads/engine-vacuum-p0171-and-p0174-codes.67888/#post-853418
QUOTE:
"X3. Do the intake gaskets and new bolts/nuts. Use Felpro gaskets, ONLY. Replace the knock sensors and harnesses under the intake while in there. Use AC Delco sensors and Dorman harnesses. While apart replace the thermostst with a new AC Delco stat. Make sure all is very very clean when reassemble. New oil change with good oil and quality filter, meaning don't use a Fram filter, JUNK! IMO"

 

[shreksbrother]

I too have these problems with these 2 codes just after a long trip from MD to MI and back in the cold blast of winter. I experienced them after I got back and went through the enclosed touchless car wash. There was a lot of vapor/steam in the air since it was 10 degrees out, it began to idle pretty bad almost like it wanted to stall, I kept the RPMs up until the wash was finished. Idle was back to normal after being in the cold dry air.Its been starting just fine like it always does, even cold weather. Slight rough idle now since CEL came on. Comes back after clearing the codes.


I also noticed that when accelerating lightly when going above 2200-2400 RPM there is a slight hight pitched whistle just as it's about to change gears. It''s always done this. Sounds like the whistle in my 73 Cougar when I had a really bad carburetor gasket leak.


Suggestions? Intake gasket? BTW I have 230,000 miles or so.


I will clean my MAF and try some carb cleaner around the intake gasket....

If it is the intake is the culprit, I found some good info:

http://www.tahoeyukonforum.com/threads/engine-vacuum-p0171-and-p0174-codes.67888/#post-853418
QUOTE:
"X3. Do the intake gaskets and new bolts/nuts. Use Felpro gaskets, ONLY. Replace the knock sensors and harnesses under the intake while in there. Use AC Delco sensors and Dorman harnesses. While apart replace the thermostst with a new AC Delco stat. Make sure all is very very clean when reassemble. New oil change with good oil and quality filter, meaning don't use a Fram filter, JUNK! IMO"

I seem to be having both issues you do...

After a long trip to NY, I, too have these two codes and have read about the intake manifold gaskets.

What I find more interesting, however, is that I seem to have the same noise as you... To me it almost sounds like an alternator squeal, but it does it under light acceleration from about 2000-2300 RPM. For me it occurs year round, though (same for you?). Figuring it was a bad bearing in something, I have been waiting a year for the sound to get worse to identify the part, but it remains completely unchanged (I've put about 20k miles on my truck this year). It is especially annoying because that is the RPM range while cruising on the highway.

So I know I need to replace the intake manifolds anyhow... It would be magical if it got rid of that annoying squeal, as well!

I think I'll order the gaskets/knock sensors/harness/oil press sensors soon and replace them. Fingers crossed!

 

[shreksbrother]

Well I changed everything today... It went very well other than breaking one of the new gaskets (2-part epoxy fixed it).

Put it back together and the idle is smoother, exhaust smells far less like unburnt fuel, check engine light has not returned, and squeal seems to be gone!

So thankful not to hear that squeal anymore... I hope it's gone for good!


Sent from my iPhone 7+ using Tapatalk

 

[Merc1973]

Well I changed everything today... It went very well other than breaking one of the new gaskets (2-part epoxy fixed it).

Put it back together and the idle is smoother, exhaust smells far less like unburnt fuel, check engine light has not returned, and squeal seems to be gone!

So thankful not to hear that squeal anymore... I hope it's gone for good!


Sent from my iPhone 7+ using Tapatalk

Thats awesome, good work! Glad to hear. My whistle is year round noise too. Im just waiting for ithe weather to warm up to tackle this job and ordered all the parts I listed from Amazon. The garage is too full of crap this winter. Did you watch a video or is there a write-up? How many hours to complete the job?

 

[shreksbrother]

I knew I needed to do it after reading about the codes, but your mention of the squeal possibly being related pushed me to do it immediately. I did it in my garage (with a newly installed ceiling heater [emoji16]) with basic hand tools in a couple of hours. I watched a YouTube video, but it was slightly different because it had cable throttle. Nonetheless it helped me fumble through pretty well.

Thanks so much for making that connection for me about the noise... I never would have suspected the squeal was from the intake manifold. I commuted today in blissful silence.


Sent from my iPhone 7+ using Tapatalk

 

[Merc1973]

I knew I needed to do it after reading about the codes, but your mention of the squeal possibly being related pushed me to do it immediately. I did it in my garage (with a newly installed ceiling heater [emoji16]) with basic hand tools in a couple of hours. I watched a YouTube video, but it was slightly different because it had cable throttle. Nonetheless it helped me fumble through pretty well.

Thanks so much for making that connection for me about the noise... I never would have suspected the squeal was from the intake manifold. I commuted today in blissful silence.


Sent from my iPhone 7+ using Tapatalk

I appreciate your reply, glad we could help eachother out. I now have confidence this should fix it! My garage is full of kitchen cabinets waiting to be installed and a 500 lb Cannon gun safe that needs to be brought in the basement .... so im stuck outside. I would love to have a heater in there.