Rough Idle After Valve Cover Gasket Job

So I went all out and replaced my valve covers, valve cover gaskets, intake plenum gaskets, cam plugs, spark plugs, plug wires, and a few other things. I also changed the oil, cleaned the throttle body/intake manifolds, and cleaned the MAF/air filter. When I put it all back together and started it, the truck ran great. As it began to idle down from the cold start, it started to sound like it was missing. Once it got to normal idle it really sounded like it was missing. It sounded like a Harley or like it had a cam in it. If I rev it up, it sounds normal. I checked for any vacuum lines not connected but they all seemed to be in place. No CEL as well. I also removed the negative from the battery and the EFI relay for 30 mins to reset the system. Not sure what the problem can be. I leaning towards something with the throttle body. Maybe the IAC valve? I did not remove and clean this. Just wondering why it would act up now? Thanks for any help!

 

Recheck all of your plug wires.

 

Definitely check your IAC

 

Also check for vac leak

 

Probably left something unplugged.. Check everything. Though harleys do sound sweet...

 

Why did you do the 'gasket job' in the first place? Was there an initial problem?

You could have one or more vacuum lines connected to the wrong ports. Did you mark them before you disconnected stuff?

 

how come new valve covers? were the stock ones toast?


definitely have something hooked up wrong, throwing any codes or check engine light yet?

 

Check all your connections to all sensors. Make sure, as mentioned, that you did not connect a vacuum line to the wrong port. Double check your brake booster vacuum line. If you have access to a data reader look at your fuel trim numbers after the engine has warmed up. If the fuel trim is a positive number, the engine is running lean, and you have some sort of vacuum leak. It happens to the best of us, but it is very possible that when you did the intake manifold gaskets, that something was not tightened down properly, or a gasket shifted during installation. Usually a small bottle of propane, and a propane torch tip can be used to find vacuum leaks. Simply turn the propane torch on WITHOUT lighting it, on a low setting, and move the tip around the intake manifold. When you get close to the leak the engine will start to run smoother and may increase slightly in RPMs due to the vacuum leak drawing in the propane into the engine.

 

I did the job because the gaskets were leaking oil badly. And I took pics of everything under the hood before the tear down.

I got new valve covers because I cracked one side by over tightening the bolt. I will be checking all connections today.

I do not have access to a data reader at the moment. However I will check all connections again. Thanks for the detailed response!

They do sound sweet

Will do.

Will do.

Will do this also. Would love to fix it without taking the TB off again...

 

So I checked all connections and then started it up. It did the same thing. Decided to take it for a spin (did not do this last night). After about a 10 min drive around the block and on a small road where I got up to 45 mph, it seems to be idling fine. However it does seems to be a tad bit high (850-900) w/ no AC. Usually it idles at about 700-750. I'll see what happens from here... Thinking back on it, I may have damaged the TPS while LOADING my TB with intake cleaner. But who knows. I think too much. It seems ok now so I'll let it be and see how it goes..

 

Spoke too soon. Took it for a drive again and the weird idle came back for a little bit and it threw a CEL. My SG showed P0130, P0133, and P0171. After looking up these codes I'm pretty sure its the front O2 sensor (bank 1, sensor 1). Any other suggestions?

 

Bump. About to buy the O2 sensor but would like to get any suggestions before. The codes make me think it has to be that O2 sensor. Just weird that it would malfunction after all the work I did which had nothing to do with that O2 sensor..

 

Replaced the upstream O2 sensor and cleared the codes. All codes cleared except the P0171 code. After some searching, this codes seems to be a pain to fix. I'm guessing (since I had the whole intake apart to install the valve covers) it's a vacuum leak that I have not found yet. Any other suggestions? I plan on replacing the majority of my vacuum lines. Hopefully this helps.

 

looking forward to seeing what the issue was

subd

 

sub'd

 

Look at it anyway you like.

 

Sounds like kigmob is talking about the maf sensor. Cleaning the maf sensor will probably be beneficial.

I'm leaning towards a possible vacuum leak after taking the intake all apart. Try getting a can of starting fluid and spray it around vacuum line connections. The engine will idle up a bit if the connection is leaking.

Good luck OP! Keep us posted. . .

 

Fixed...