TS14

Hello I have a 2000 silverado 4.8L with 199,000 miles and the sevice engine light came on and I had the codes read and was po171&174 was told it could be the MAF or the O2 senors so I bought some MAF cleaner and cleaned it. Light went out only to come back on. When I start it up in the mornings it idles really rough and it is almost like back in the day when there were carborators and the choke would stick. spits and spuders. and my gas milealge has gone from 16-17 to 8-9. It seems to be alittle worse on the cold mornings. When I sit at a stop light the rpm's jumps up and down and almost like it is going to die then back up.Getting very frustrated and dont have the money to start guessing what the problem could be.

Thanks

MDTAHOE

I can start by telling you the O2 sensors are not the problem they are actually what is seeing it. You need to check the fuel pressure and volume. Also the engine needs to be checked for failed intake gaskets. The coolant temperature sensor could also cause it if it is reading warm when the engine is really cold.

TS14

Thanks for the reply. How do I check the fuel pressure and volume? also is there any test I can do at home for the Intake?

Biggie360

fuel pressure is checked by plumbing a fluid pressure gauge into the fuel rail somehow. to test volume, you can pull the return line and plumb THAT into a gas jug with a few feet of rubber hose. to test the manifold gaskets, you'd want to do an intake manifold vacuum test. a chiltons or hanes manual could tell you more if you can't get more help.

RedBaron921

I have the same problem with my truck right now and can't find the issue, however I do have the 6.0 liter in a 1999 truck. I tried to clean in the MAF and it didn't help then I did swap out the MAF sensor with a know working one and it did not help.

This problem is driving me nuts.

tat2dup81

yeah my 04 is having crappy mpgs. first my cat went bad and then o2 sensor. replaced all of right side. still had bad mpgs. cleaned map sensor, no better. finally took to dealership, said my #3 cylinder was bad due to plug wire being bad. my code was p0300. but i also heard of mpg issues with fuel pressure or leak in gaskets. i basically went from 16-18mpgs to 13-14.

TS14

OK so I did the carb cleaner test on the intake and the engine idle went from rough to smooth, So is it safe to say that it is my intake gasket? If so are they hard to change? I do know some about cars and think I can do it if it is not to hard. Does anyone have any step by step instructions on how to change it?

Thanks

RedBaron921

Well got the truck from the repair shop, turns out the intake manifold gaskets were leaking and needed replaced. They were able to change them out within 1 day, I believe this is something I could have done but with the weather in the single digits, well you know. Thought I would share the information to help someone else.

I cleaned the MAF but that did not help, I even tried to spray carb cleaner around the base of the manifold to see if it would effect the idle, didn't really notice any change. I suspected it was the problem but it was a guess. How difficult is it to change the gaskets?

Red