For the past month or so i've been having problems with my idle. Very rough, loopy and excessively lean. I had a hard time searching for symptoms and fixes so this should make it a lot easire for everyone. Regardless of modifications these are good things to check for as this is what i did to fix my bad idle.
Things to check for...

A Vacuum leak will throw a CEL system too lean.
Faulty MAS (Mass Airflow Sensor) will throw a CEL also.
Faulty TPS (throttle Position Sensor) and ISC(Idle Speed Controller).
Faulty FPR (Fuel Pressure Regulator) and Fuel Pump.

-PCV Valve (Hold it parallel to the ground and jiggle it side to side. Then without moving much blow into the threaded side. If should blow freely. If you feel resistance which then opens up after you blow harder you need to replace it. You can also turn the PCV valve with the threaded side pointing the ground while blowing into it. If it plugs then it needs to be replaced.)

-EGR valve stuck in open position (Remove and clean with Carb cleaner. Ensure the valve closes completly and without excess resistance)

-Mass Airflow Sensor (Use a MAF cleaner to remove grime from the sensor.)

-Loose bolts (Intake Manifold to throttle body and also Intake Manifold to Engine Block)

If the above all check out then do a pressure test.
- Remove the intake and pressurize from the throttle body on
- You can use Brakleen, Intake & throttle Body Cleaner, Carb Cleaner etc and spray it over where you suspect leaks (Throttle body to intake manifold, intake manifold to engine block, all vacuum connections, AND the FUEL INJECTOR INSULATORS(Little black rings in between the fuel injectors and the intake manifold)

If you've removed the fuel rail from the Intake Manifold at all these spacers should be replaced. The spacers get hard after a while due to repeated exposure to fuel. They lose there flexibility and usually don't seal correctly. The injectors will never seal perfectly the same way as before so you need a spacer that has good flexibility to seal the gap correctly. These can either be purchased at your dealership or at most auto parts store.

-If you've done all the above then your problem is most likely not a vacuum leak.

Other causes for a rough idle can be faulty O2 Sensor(Will throw a CEL), Damaged Catalytic Converter(Will throw a CEL), Incorrect Spark Plug Gap, Damaged Spark Plug Boots/Wires(Should show signs of arcing across the tops), or dirty fuel injectors.

Well just wanted to share some information I've learned. If anyone wants to add anything feel free, maybe we can make this a sticky or something.

 

Thanks for the write up!

 

good write up. i am experiencing the same issue and can't figure out what is wrong.

 

Great write up, thank you.

 

I accidently burnt up that fusable link on the positive battery terminal, and dropped some solder in it and that dont allow voltage to flow through great, and is causing the MAF to get low voltage. Just another thought on what a rough idle could be caused by.

 

low voltage at the MAS could be because it's dirty also...

 

i have been having the same problem forever.
also if you have the piggyback, make sure that your wires are secured.

 

about those fuel injecttor seals... I sprayed them with some spray-a-gasket. Its messy but it worked great, I just had to make sure that nothing got on the tip of the injectors. I threw in a bottle of STP injector cleaner after just to be sure.

 

My car idles rough in drive and a little bit in reverse. I had a broken vacuum line, one from the IM to something on the left side, and changed my pcv valve. It helped a little but it still idles really rough. How would I check to see if the TPS and ISC are faulty or clean them or something? And how would I get to the EGR to clean it? Thanks for the help and sorry if im thread jacking.

EDIT: Car is not throwing any codes at the time being.

 

Having the same problem, wideband is reading from 16.5-17.5 at idle, but normal driving/cruising the a/f ratios are great, any ideas?