Here is alot more information.
I have a problem with my 2005 Chevy 1500 Silverado 5.3 liter engine with an automatic transmission and the truck has 125,000 miles. I had the transmission fluid and transmission filter changed and the first time I started the engine the truck idle was low and I thought the engine was going to die. It appears to idle at 400 rpm. I drove two or three miles and after stopping at a few stop signs the rough idle continued and the check engine light came on. As soon as I accelerate the truck runs with fine and when I push the accelerator down hard acceleration is strong. I do not think the transmission service and the rough idle are related. The mechanic that worked on my truck has repaired my mother’s and brother’s pickup trucks for years. The next morning I put a can of Sea Foam in the gas tank that was 80% full and drove 15 miles and the rough idle continued. I was hoping an injector that was partially blocked.
I talked to the mechanic and approved changing the spark plugs. The spark plugs were original. The low idle problem remained. He checked the oxygen sensor and the senor reading was 600 and then the reading dropped to is 13. The mechanic thought the problem was the oxygen sensor so I okay replacing the senor. When he changed the spark plugs I also had him change the fuel filter, oil and filter and belts.
Changing the oxygen sensor did not correct the problem. He stated the reading on the new oxygen sensor gave the same readings as before, starting at 600 and then dropping to a reading of 13. He looked deeper and hooked up the truck to his diagnostic machine and determined the number one cylinder was misfiring only at idle. He stated the only cylinder that as missing was the number 1 cylinder. He listened to the fuel injector on the #1 and he can hear is clicking. He checked fuel pressure and the fuel pressure was good. I think he said the fuel pressure was at 60 lbs.
He thinks I have a head gasket issue and this is why the number 1 cylinder is missing. The mechanic stated these Chev’s have weak head gaskets. The mechanic was informed I had added Sea Foam to the gas.
Normally I have the oil changed at 3,000 miles and I do not need to add oil so it does not burn oil excessively. A couple of times I when over 4,000 miles between changes and I did had oil to the engine.
After the spark plug and oxygen sensor were changed the check engine light was off and after a few miles of driving the check engine light came back on. Friday night I drove to 196 miles to my home. At above idle it ran normal. At my first stop at 53 miles, the truck idled smoothly while at the gas station. I was still hoping I have a partially blocked injector I added another can if Sea Foam 90 miles into the drive. Unfortunately at my next stop and while I ran errands Saturday, the rough idle continued.
I stopped at an Autozone Saturday morning and they gave me the errors codes. P0300, P0131 and P0171.
I would like another opinion and after reading the details of the codes I will not have the mechanic change the head gaskets.