Hello,

Recently I have went on a cleaning spree on my 01 CL type-s. 137,000 miles. And at idle I hear a drumming/thumping sound of a very faint misfire. Haven't pin pointed it to what cylinder it is. But it started after I went on a carbon cleaning spree.

Idle is rock solid, the car doesn't shutter or vibrate heavily. I unplugged each coilpack 1 by 1, the idle changed to be worse. So each coilpack should be fine. So maybe this isn't a misfire, or maybe it's very very faint.

I did the following:

• Cleaned black soot, unblocked EGR ports under top manifold cover, replaced gasket
• Cleaned EGR valve, unblocked buildup, replaced gasket
• Replaced IACV and OEM gasket (in hindsight should have did a good cleaning around the stepper motor
• Replaced throttle body paper gasket, cleaned throttle plate
• Sprayed MAF cleaner in every port on the throttle body (map/iacv)
• Techron bottle in the gas last 2 fill ups
• Seafom treatment via vacuum hose

Plugs were replaced 2,000 ago with quality NGK iridiums (ZFR6FIX-11). Didn't have a light missfire below.

• My thoughts are a vacuum leak when I had to scrape away the old paper gasket
• The new IACV leaks or is causing misfires
• Maybe this isn't a misfire I am hearing
• Plugs became fouled after cleaning

Let me know! Doesn't smell rich or lean.

 

valve adjustment would be next.

plugs could have been fouled if you didn't do seafoam before replacing. Pull all of them to check!

 

Did you replace the IACV with an OEM one or aftermarket?

 

Aftermarket off Rockauto, they are usually pretty good for not picking the most crappiest of aftermarket. But I see the point you are eluding to.

Maybe i'll try to separate the OEM stepper motor from the bracket, and clean around the counter weight.

 

Yeah our cars are pretty particular about some parts being OEM, that being a crucial one.

 

Please take a look at this thread:

https://acurazine.com/forums/second-...o-iacv-956070/

I'm betting that going back to OEM will solve your problem.

 

Oh wow, looks like I am not crazy. Thank you so much for digging into this! I'll give my old one another shot, or maybe just order a new Denso one?

Now that you mention it, that popping sound only happens when the car is hot, and comes to an idle (after driving).

Shame I didn't do my research on, an IACV generally isn't such a sensitive electronic.

 

Wow, idle is very different than it was with the off-brand IACV. Seems smother now, and under idle-load (AC ON) no more popping sounds from the intake (good thing it wasn't spark missfires).

Now I noticed there is a vacuum solenoid right above the brake booster, that takes 1 vac line in, and sends it out towards the fire wall. It makes quite a bit of clicking sounds from actuating - i'd imagine this is engine feedback for idle vac? Would it be concerning for how loud it actuates? It is quite audible, pulling the throttle cable makes it go away as the engine revs, but returns once engine is back at idle.

It's the vacuum purge solenoid I think. Denso MX136200-2110

cheers