Recently bought 04 TSX with 150k miles

changed spark plugs, oil+filter, transmission fluid, air filter
tried to seafoam, maybe incorrectly: the seafoam was fed to the engine rather slowly, so no thick white smoke - only some blue for a while. Or this maybe the way it should be, if previous owner fed the car with regular gas (have no idea about that).

still have the following issues:

1. Rough idling (as it was said, "hunting" idle: dips to 500rpm once in a while and then back to the normal) even when engine is hot. A lot of discussions about that, no solution.

Note: when I put seafoam to engine oil (before the change) - this thinned the oil a bit and idle RPMs became higher ~700 but rough idling disappeared. After an oil change - enjoying rough idling again!

2. Purring of the engine (vibrations) - occasionally (on 'parking', on 'drive' at stops). Some people say it is normal for 4 cyl, or when engine is cold, or both. Since I have not noticed any correlation between vibrations and engine temp, will disagree that it is normal.

3. Whistling/whining/whizzing noise from the engine, RPM dependent, starts at ~1500, more pronounced under load, speed independent (that's why it should not be a transmission related niose). The noise is very close to the sound of a turbine in turbodiesels

Note: I tried to seafoam the engine, to burn the remaining seafoam I made 3000 RPM for 3-5 minutes. Do not know what influenced more: spinning the engine or seafoaming it, but for the next day the noise gone! I thought I went deaf it was so quiet! But in two days the noise returned back.

Any experience with that or ideas how to fix it?

 

The idling issue is weird. My TSX does it too. I used to have a Lexus RX330 and it was smooth idling ALWAYS. I know the vehicles are a big difference but that's just for comparison purposes.
My engine seems to "purr" when accelerating. I have to drive it a little more before I know if it is just from a cold start or more often.
I would love to get rid of the purring noise because it's annoying but I wouldn't even know where to start. It sounds like a spaceship taking off.

 

try and give the car a good hard drive and see if it blows out any cotamination left in fuel system, check plugs are in good and deep and tight

 

Totally agree about purring noise,

spark plugs I just replaced and tightened to 12 lb-ft with anti-seize. But i think this could not be the reason: spark plug change haven't influenced these issues.

About blowing out contamination: when the engine is cold the emission gases have noticeable color and smell, but pretty soon color and smell disappear. Is it normal? I really hope that this is due to gaps between cold piston and cylinder walls, the engine is just burning a little oil

 

To figure out what is this noise about, I started the engine without serpentine belt - the noise was still there.

Took my car to a mechanic, he said that this whizzing noise is probably due to worn out timing chain tensioner or guides or stretched out chain.

Does anyone had such an experience? What symptoms? What are the reasonable prices for parts/labor?

 

This thread is a bit old but I have some information to share in terms of cost of parts and labor. I received it from King Motorsports:

Cost breakdown
Toda Timing chain $266.00
Toda Tensioner $220.00
Labor $600.00

I'm thinking about doing this but not anytime soon.