2007 w/ 73,000 miles

New motor mounts helped with rough idle somewhat. The throttle body was the real issue. I removed the throttle body because I could see some gunk around the rim with the air box and accordion tube removed. Once I got it off and saw the other side and felt how rough the plate inside was to move, I picked up a $5 can of throttle body cleaner and 1500 grit sandpaper.

Spray, sand, spray, sand, repeat until clean. Re-assemble. While in there, I used plastic safe MAF cleaner on the air box MAF intake tube screens. Left the sensors alone since I had cleaned them in a previous attempt to fix the problem.

I started the car and it ran at high RPM's and would not drop down to 850 where it usually runs at. I disconnected the battery for 15-20 minutes, reset the ECU and then the brake stomp dance. Low and behold, the RX is running as smooth as can be. It was an instant improvement.

Air conditioner test: Before cleaning, with the a/c running, it would never increase the RPM's when the compressor kicked in and would cycle on/off about every 5 seconds and rattle the whole car like mad. Not anymore!

Thanks for all the DYI from other RX owners. I'm sure the dealer would have just sold me I need a new $450 TB.

DYI note: I forgot that coolant runs through the TB and did the work when the car was hot. Save yourself a blister and do it cold. Popping the overflow tank cap might help to keep coolant out of the engine bay when you remove the two rubber hoses.

 

Can you go into a little more detail about what you did? I have the same thing happen but I just assumed that it was the AC load and didn't worry about it.

 

I've read in other posts that 'some' vibration is normal. Enough that I started to believe it myself, especially since my RX has almost 75,000 miles. Who would have ever driven a $30,000 car off the lot new if it was?

The procedure was simple enough. I'm a software developer so suspect pretty much anyone can do it.

1. Remove the air box by applying just enough force on the front of the air box on either corner where the clips are, to clear the front intake tube that joins the air box to the front of the car. There are two rubber nipples that pop away on the front and two on the bottom when you lift it up and out. You don't need to take it all the way out because there are some small tubes that attach to it. Just lift it up enough to get it out of the way.

2. Unscrew the adjustable rings on both ends of the accordion tube to separate it from the air box on one end and the throttle body on the other. You can now see one side of the inside of the throttle body. It's aluminum with I suspect a copper valve inside. Anything you see in there that is not aluminum or copper is 'gunk' as hard as varnish. The valve may have an 1/8 " darker ring surrounding the outer surface. That's okay.

I used my finger to push open the valve to inspect the other side. That's where the real problem was. The varnish coated the entire surface of the throttle body and built up enough to prevent the valve from closing properly or moving freely. I could feel it scraping the valve as I opened and closed it. I suspect this gives the ECU an incorrect reading on the throttle body position.

Fix:
3. Unclip the wire cluster from the throttle body on the left side.

4. Remove the two coolant hoses on the top and bottom of the throttle body. I made a mess when coolant shot out. I suspect if I had removed the cap on the overflow tank this could have been prevented this. Next time I will ad also wrap a towel around the top on as I pull it off to catch any that might come out. Remove the lower one after step 5.

5. There are 4 10mm bolts on the front of the throttle body. Remove them and the TB comes right off.

6. Gently remove the pink rubber gasket that stays in the remaining housing and GENTLY wipe it clean. Put it back in. There is an alignment tab. You can't get it wrong.

7. Wipe out any debris that might have gotten in the plastic housing. Should be nothing more that small grit or you have a major leak.

8. Using a can of throttle body cleaner and 1500 grit sand paper. O'Reilly had them both. The gunk can be hard as varnish and will not dissolve by simply spraying it. 1500 grit isn't rough enough to hurt the metal parts so just spray an area and wet sand. I cut my sand paper into 2" wide strips so I could do a small area at a time sanding side-to-side using two fingers. Not in/out and cause an out of round condition just in case. I used the whole can by the time it was clean. I sanded the outer rim and edge of the valve too. I used one final spay to clean up the residue and wiped clean. It will look pretty much brand new when done.

9. I used MAF cleaner and sprayed and wiped down the two screens on the inside of air box. I had cleaned the MAF internals previously.

10. Reassemble.

11. I reset the ECU and performed the brake stomp procedure afterwards because it was idling very high due to the new TB position as seen by the ECU.

That was it. The A/C rough idle went completely away. The vibrations that rattled the car body in reverse when I backed out of the garage went away. It has considerable more spunk from a stop.
Now the only sound left is the fuel pump working it's little butt off on WOT. I got the right tool to remove it so I can clean the sock this weekend.

I took a few pictures but nothing that can't be found in the DYI section.