Cold loud start
Thread Starter
Racer
Joined: Aug 2016
Posts: 1,385
Likes: 157
From: New South Wales
Cold loud start
Can someone tell me why the ISF is LOUD at cold start for 30 ish seconds is it the exhaust valve being held open longer or longer duration ,to heat the cats up faster when cold for emissions, this is my guess, after a short time she goes a lot quieter, just interested cheers
Driver
Joined: Mar 2016
Posts: 147
Likes: 2
From: FL
Can someone tell me why the ISF is LOUD at cold start for 30 ish seconds is it the exhaust valve being held open longer or longer duration ,to heat the cats up faster when cold for emissions, this is my guess, after a short time she goes a lot quieter, just interested cheers
Pole Position
Joined: May 2016
Posts: 255
Likes: 26
From: NSW
Like you mentioned earlier, every ISF does it. Its just more noticeable when you have an exhaust/headers etc.
I had always wandered this myself and did read about it. Cant remember where now that i want to find it but basically it was part of the cold start mapping of the ECU compensating for higher revs to minimise / prevent possible stalling.
Also had to do with the lack of heat in the engine on cold start ups vs once warmed up. Fuel doesnt burn as effeciently on a cold vs warm engine (lack of vaporisation) so the air / fuel ratio is slightly different on a cold start. Engine speed is higher at start to help burn the excess fuel thanks to ECU mapping and once the engine begins to warm up, excess fuel is dealt with, the air / fuel ratio leans back out to normal
I had always wandered this myself and did read about it. Cant remember where now that i want to find it but basically it was part of the cold start mapping of the ECU compensating for higher revs to minimise / prevent possible stalling.
Also had to do with the lack of heat in the engine on cold start ups vs once warmed up. Fuel doesnt burn as effeciently on a cold vs warm engine (lack of vaporisation) so the air / fuel ratio is slightly different on a cold start. Engine speed is higher at start to help burn the excess fuel thanks to ECU mapping and once the engine begins to warm up, excess fuel is dealt with, the air / fuel ratio leans back out to normal
Trending Topics
ClubLexus Stories
Celebrating Lexus & Toyota from Around the Globe
8 Tips for Improving Your Hybrid or Plug-in Hybrid's Efficiency!
Michael S. Palmer
10 Best Lexus Models No One Remembers
Joe Kucinski
TRD Off-Road Premium: Best 2026 4Runner, Except This One Thing
Michael S. Palmer
Top 10 Lexus & Toyotas to Drive Before You Die!
Joe Kucinski
Top 10 Lexus/Toyotas With The LEAST 5-Year Depreciation
Joe Kucinski
Lexus LC500 Convertible Auction: A Preview of Rising Values?
Brett Foote
GX 550 vs TX 550: Best 3-Row Luxury Lexus Family Hauler
Michael S. Palmer
9 Best Lexus Models You Can Buy for Half Price (And 1 You Shouldn't!)
Joe Kucinski
2026 Lexus NX Buyer's Guide: Models, Features, Prices & More!
Brett Foote
It always sounded to me like it was oil getting to the top end. There's no way the exhaust timing can be extended or lift changed with the engine. The only thing the VVTi does is change relative lobe center to advance or retard the cam. Maybe, just maybe, it's because the locking pin in the exhaust cam is still in place and the exhaust cam timing is optimised for starting the engine, and once sufficient oil pressure has released the cam drive lock pin, the cam timing is adjusted for run not start. That would be my guess from having heard this many, many times.
Driver
Joined: Mar 2016
Posts: 147
Likes: 2
From: FL
It always sounded to me like it was oil getting to the top end. There's no way the exhaust timing can be extended or lift changed with the engine. The only thing the VVTi does is change relative lobe center to advance or retard the cam. Maybe, just maybe, it's because the locking pin in the exhaust cam is still in place and the exhaust cam timing is optimised for starting the engine, and once sufficient oil pressure has released the cam drive lock pin, the cam timing is adjusted for run not start. That would be my guess from having heard this many, many times.
Yeah I thought this was basically common place on cold start. My ISF does it and my old E92 did it as well, that car was hella loud on cold start and then would mellow out fast after about 20 sec or so. But that car had air pumps to warm up the cats on cold start so that's why it was loud on cold start(but it did sound beastly on first fire up haha)
