The idle is so rough I must throttle the gas to keep the engine running.

Conditions that cause the rough idle.

The outside temp. must be 50 degrees F or 10 degrees C and below.
When the engine is at operating temp. the idle is much smoother.

I replaced the MAF sensor and that helped a lot but I am still experiencing a rough idle. I no longer must throttle the gas the engine will now run but is still rough.

I replaced the water temp. sensor no change was noticed.

The typical vacuum leaks have been addressed.

Any ideas would be most helpful.

 

This is likely a vacuum leak. In the cold, materials and metals contract (shrink) this can cause seals or worn gaskets not to seal as they should, tubing wont be seated or seal properly, this causes vacuum to decrease which will cause your rough idle issue, once the car warms up, things expand and seal up. I have the same issue, I'm thinking I need to replace the gaskets on my intake manifold upper and lower. Check you PCV hose to insure it isn't cracking.

 

Ditto on the PCV hose. Fixed mine with the same problem.

 

Had same issue with mine. I addressed every possible vacuum leak, but it wasn't until I replaced the lower intake manifold gaskets (plenum), that I got results. Previous owner had replaced upper only a few months earlier, but not the lower ones. Has run smooth ever since.

 

I replaced my Upper and Lower Intake Manifold gaskets. Pretty sure my upper was the cause but hard to tell on the lower. At any rate, The car now starts fine, and idles like a champ. I still have an issue somewhere as I am still getting the cruise not available off and on and my brakes are hard to press when the engine is cold.

I replaced the Brake Booster to Manifold tube with a new one and the PCV Hose is in great shape. I have the IMT o-rings on their way and will be trying that next.

 

I replaced the IMT O-rings and it was needed, the lower was hard and not pliable.

I still get the cruise not available occasionally, I think this is because there it a small leak where the brake booster line seats into the manifold, I'm having trouble finding out the name of that part.

banks lean code is gone, now getting the p0420 error code

I put cat cleaner in but may have to do the sea foam trick.

once I get the part for the vacuum leak I hope it clears it up.

 

When I changed the Bottom IMT out I just stretched the o ring around the connector I didn't have difficulty and it didn't break or rip ...Are you referring to Brake Booster Check Valve?

 

no, the part the brake booster line plugs into. I think the o-ring in it may be bad but it's leaking a bit.

 

I bought my O-Rings at the Dealership I believe it ran about $6. Very Inexpensive and it solved a cold start issue similar to yours.