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I almost hate to make another one of these rough start threads, but my 06 Elise is doing something quite odd. This occurs only on cold start. I turn it on, and it idles fine - totally normal. If I give it some gas, though, the revs go DOWN and it stumbles for 1-2 seconds and returns to the totally normal idle. This is repeatable a few times before it starts to behave normally. After maybe 30 seconds to a minute of idling/warm up time, the car is totally normal. It drives great, pulls strong, and never idles rough on stops. :scratchhead:
Any thoughts? Again, it's an 06 elise with a basically stock drivetrain and 82k miles on it.
As an aside, there is also a bit of a 'whistle' on start up when I give it a bit of gas, but this goes on even after it's running normally until I've been driving a few minutes, then goes away. I think the whistle is the air filter not sitting quite right in the box, then gets seated as it warms up. :shrug:
A stumble is consistent with poor A/F control. I expect that at cold start the A/F is open loop (only driven by MAF readings). After the car is warmed up I expect that the fueling is corrected by the oxygen sensor reading and is thereby in closed loop feedback control. Maybe you have a small vacuum leak; how are your fuel trims (vs RPM or MAF)?
I almost hate to make another one of these rough start threads, but my 06 Elise is doing something quite odd. This occurs only on cold start. I turn it on, and it idles fine - totally normal. If I give it some gas, though, the revs go DOWN and it stumbles for 1-2 seconds and returns to the totally normal idle. This is repeatable a few times before it starts to behave normally. After maybe 30 seconds to a minute of idling/warm up time, the car is totally normal. It drives great, pulls strong, and never idles rough on stops. :scratchhead:
...
This behavior is completely normal for the Lotus tune in the Elise/Exige ECU. I seem to recall reading a thread many years ago that the engine intentionally runs a little rich for the first 20 to 30 seconds. Think of it as the equivalent of a choke on an carbureted engine (choke causes it to run rich) to help with cold starts. However, it doesn't seem that the ECU is programmed for smooth operation when you give it a little gas in that initial 20 or 30 seconds. Lotus probably could have worked more on the ECU tune and fixed this (Toyota cars with this engine don't have this behavior, as far as I know), but they probably didn't feel it was worth the effort.
I also recall one theory that the ECU intentionally runs rich to help heat up the catalytic converter at startup for emissions control reasons. While running rich would heat up the catalytic converter aster, I don't know if that was the real reason.
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