Rough Idle After Valve Cover Gasket Job

Got the new hoses in. Gonna install them tomorrow probably. I think I will also remove the TB and upper intake manifold, and check every bolt that holds the intake together as I reassemble. I will probably also clean my maf a bit more thoroughly. Hope this will get rid of my code. I will keep this thread updated with results.

 

I replaced the vacuum hoses and rechecked the TB/manifold bolts. Everything seemed fine. I also cleaned my MAF thoroughly and let it dry for 30 mins before putting back in. I also added a can of sea foam to the tank to help clean out the injectors. I cleared the code and it came back within 30 minutes . I don't know what it can be. I haven't brought myself to bring my truck in to the dealer or a shop to get diagnosed. I hate doing that. It's just strange how everything is fine besides a low/chugging idle every now and again and ONLY when the engine is warm. The truck runs great when driving around. It's fine at high RPM's and has no stutter or hesitation when accelerating. Also, I've noticed the past 3 times I cleared the code, it always came back when the truck was idling, not at high RPM's or anything. Does anybody have an idea of what the problem could be? What exactly are the signs of a bad MAF sensor? Does this seem like more of an air/intake problem or a fuel problem? Thanks!

 

Good advice on how to clean it, however that is the MAF sensor, not an oxygen sensor.

While you have done a great job cleaning everything, that does not mean you will fix it. A faulty sensor, even one that is just slightly off, can still send slightly off data, causing an issue. I had this exact same problem with a Ford Explorer the other week. Constantly setting a P0174 code I believe. End result was the MAF sensor was bad, even though the data LOOKED correct.

That being said, was there any chance that this code was there before you started any of the work in the first place?

 

Thanks for the reply! And no the code was not there. There were no codes prior to the work. Once the job was complete and I noticed it was idling funny, it threw 3 codes. P0130, P0133, and P0171. The first two codes lead me to believe the upstream O2 sensor was bad. I figured this was also causing the P0171. I replaced the O2 sensor and reset the CEL. The P0130 and P0133 have been gone since but the P0171 remains.

 

here is list of possibilities:


DTC P0171 - System Too Lean (Fuel Trim) has a number of causes. these are the more likely possibilities.

• Air induction system. Any air leak between the Mass Air Flow sensor and the intake manifold will cause this DTC.
• Injector blockage. You would need to do an injector balance test to determine which injector(s) are restricted.
• Mass Air Flow Meter. This should throw a code. You can take it out and clean the inside with electronic switch cleaner.
• Engine coolant temperature sensor. If the CTS is sending the wrong information to the PCM, it could cause the engine to run lean.
• Low fuel pressure. You need to do a fuel pressure and volume test to check this possibility.
• Leaky exhaust system. A leak in the exhaust system can dilute the exhaust gas resulting in a false reading.
• Open or short in the O2 sensor wiring.
• Bad O2 sensor.
• A bad PCM.

 

So many things...

 

I would get a new maf from a wrecker and give that a go before diving into some of those other possibility's.

 

This thread is so well written, there is no way this problem can persist much longer.

I like the known-good MAF swap idea next.

 

Did you use new gaskets when you reinstalled the throttle body and intake manifold? I would try to rule out a possible vacuum leak before I tried replacing sensors as they get get expensive quickly!

 

Dumb simple suggestion....

Did you check the ECT sensor? I was doing some work around my engine (2.7L) and forgot to plug it in and my temperature gauge was dead until I looked around and found it unplugged.

In your case, the ECT sensor may cause a P0174, so its worth a double or triple check as the sensor can lay disconnected and tucked away and be a bit hard to notice.

 

Any updates? It would be nice to have a full story. Thanks in advance.

 

No updates. Currently in NYC for a little vacation. When I get back I will check the ECT. I may also find a good used maf to swap out and see if that's the problem. I still just don't get how it coincidently went bad when I changed my valve cover gaskets. All I did was remove the intake and let it sit in my garage...

I would like to find someone who has some sort of live data reader so I can check all of the sensors and really see what's going on.

 

same thing happened to mine when i also replaced the covers. mine was the spark plug wires were not in the right order.

 

I replaced both intake manifold gaskets when I removed them to do the valve cover gaskets. I did not replace the TB gasket. I did dremel out the little semi circle to make it a full circle just for the hell of it. I made sure the gasket had no metal shavings hanging off so it would sit flat. I may get a new one just to be safe?

 

So today I examined under the hood again. Everything looks good. I decided to spray a little MAF cleaner around my intake to check for leaks. I'm pretty sure I heard the engine slightly idle up when I sprayed around the TB and IAC valve. I'm thinking my IAC valve gasket may be leaking. I did not clean or check the IAC valve when I cleaned the TB. I'm thinking I may have caused a leak when I was pounding the TB with cleaner. I think I'm gonna pull the TB and replace the TB gasket along with cleaning the IAC valve and replacing its gasket as well. I will also check everything else while it's apart. I sure hope this fixes it. I will keep you guys posted. Anyone know the part numbers for these gaskets?

 

So my problem may be fixed. I took off the IAC valve and cleaned it. I also connected it to be battery directly to ensure it was working properly (I checked it before I cleaned it and it worked fine). The old gasket looked fine as well. I was beginning to think this would not fix my problem. I noticed when I pulled off the old TB gasket that it was not oriented correctly. Maybe this could have been my problem? Anyways I put the new gaskets on and pulled the efi fuse for about 15 min. When I started the truck it started strong and slowly idled down to about 750 rpm. It remained here and did not drop low to 650 rpm like it used too. No CEL as well (still haven't driven enough to know for sure if it will come back). I hope this fixes my problem. I will update this thread once I know if it is fixed for good.

 

Good info. Thanks for the update. Let us know if its stay good.

 

Seems to be fixed for good. No CEL. Must have been the TB or IAC valve gasket. Thanks for the help guys!

 

I got the same problem, in a Nissan Frontier, it was fixed just replacing 2. Small hoses that are like 1/4" one came from the manifold (back)and the other ones is in the back below the manifold , the 2 where very old , and one had a hole , maybe it opened when replacing gaskets