nishant11

I have 2003 TL-S with 193000 miles. Very reliable however now has random rough idle once in a while for last two months. Unpredictable. Happens about once in two days. Sometimes when cold, sometimes when normal temperature. Cannot know when to take it to mechanic

When rough idle, car shudders badly- engine rpm fluctuates by about 100 rpm- Half the line. Only twice it died at idle at stop light. No problem in driving. Shudder vanishes the moment I touch accelerator pedal. No change in fuel consumption- Good. To prevent stalling in busy traffic, I now do left foot braking with slight accelerator pressed.

No codes. No change in shudder with A/C on or off.

In view of this, I have come to a conclusion that the issue is not engine related. May be A/C clutch is dragging even when not switched on. It may be about to die.

With hood open and normal running even when no rough idle, I can hear occasional scratching noise for few seconds which does not go even when I go in the car and hit A/C off button.

Because I suspected Idle Air Control valve issue, I removed existing one to clean. Looked alright to me and nothing to clean. Refitted and status quo on rough idle continues.

Any suggestions?

RONE

I had pretty much the exact same thing happen, and it turned out to be a bad transmission. Hopefully that's not the issue for you.

Skirmich

Sounds like IACV.

01tl4tl

verify: you removed the TB from engine, took to workbench and flipped it over- remove cover to IACV then removed the actual ROD with air slit, from inside the chamber/bore
the slit is what clogs and the chamber gets gummy
Clean both with carb cleaner or deep creep

01tl4tl

have you done the egr system, clean INSIDE the intake manifold when removed from engine?

does this occur ac on and ac off?

nishant11

My mechanic cleaned throttle body and IAC and informed nothing much to clean.
As I mentioned, A/C on or off does not matter.

How bad transmission can affect this is not clear to me. When in drive and engine running, it is in converter mode.

My premise is that if it is an engine issue, it must trigger fault code based on OBD-II logic.

Chojun

Just a couple basic questions:

Have you ever cleaned your EGR system?

Do you use 91 octane minimum?

Have you tested your coil packs?

01tl4tl

does your mechanic know the specifics of the TL? may have no clue as to our egr systems issues, not just a remove the valve and clean the 2 holes type deal
Most cars never require such a service!!!
The actual egr valve may be hanging/sticking too

The IACV= unless he stated that the rod was removed and cleaned, don't expect he knew how to do that job either!!
I trust no one!
We have members who allegedly read the diy then remove only the top cover of engine and poke around a little in the egr end there- thinking and claiming to have cleaned the system! nope- just made it worse!

thoiboi

Agreed with everyone about EGR and IACV


IACV is one of the more finicky valves.. I couldn't even end up cleaning mine but replacing it outright fixed my rough idle.

Chojun

Yup the service manual only covers the EGR system in case there's a DTC. But lots of experience here dictates that your ride can go rough with a dirty EGR and no codes.

If it's been more than ~75K miles since it's been cleaned then chances are yours is dirty. Grab about 2-3 cans of carb cleaner and a few hours and yours can be nice and shiny again - check our DIY section.

01tl4tl

to be clear- the egr system cleaning means removal of the intake manifold from the engine- to be placed on a workbench and the passage INSIDE the manifold casting that runs thru entire length of the manifold, must be cleaned of exhaust gunk

When working correctly- the EGR valve opens and allows a small amount of exhaust gasses to flow into manifold (smog equip b.s.) for reburning
The passage and the ports to each cylinder get clogged and the whole thing goes whacko
The passage needs to be reamed out-poked with wire coat hanger and soaked with 3 cans carb cleaner to get it reasonably clean- for return to service,
As noted above- needed every 75kmiles = based on our mega moderator with over 650,000 Miles on his 00TL = done it a few times!!

The valve itself is closed at idle and full throttle, open the rest of the time
If the valve is sticking- the arm of it can be lubed. The possibility its open at idle exist. That would make it run really bad right at that moment

Its worth the 2 hours at a casual pace to remove the manifold and do the cleaning. While in there- the Throttle Body comes off along with the manifold.
Clean it, and the Idle Air Control Valve IACV accessed thru bottom of TB body

Until you know BOTH iacv and egr systems are working correctly- all rough idle questions should be put on hold

Note The use of any spark plug except the correct NGK or Denso- the special ones specified on hood sticker and in owner book, about 8 dollars each- for a reason
Not a normal spark plug! other brands will have running problems very soon after installation, within weeks or months