The first stomp on the "go" pedal after engine warmup produces rapid, oscillating hesitation, very rich mixture for a few seconds, and rare instances of fuel cut. It will self correct in perhaps 30 seconds or so of high speed driving, when (presumably) the air temperature thermistor in the AFM finally reads the correct air temperature, air coming through an enlarged opening where the stock air cleaner housing was.
I'd like to know if anyone else has had this happen with an air cleaner located under the hood. I've got an HKS air cleaner (pretty far forward) because it appears to present the least impediment to airflow. Yeah, it does not clean the air very well, but I'm careful to drive where there is no construction dust, etc.
The air temperature thermistor is needed because the Karman Vortex AFM is a volumetric, not mass flow device, so it corrects for incoming air temperature. It is encapsulated by the plastic nub and possibly epoxy fill on the bottom of the Karman sensor. Thus it lags reading the true incoming air temperature. In the stock application this is of no concern, because air is always pulled in from in front of the radiator bulkhead. However, that is not true when air is taken from under the hood, particularly at low speeds, and particularly with the bottom engine cover in place.
There are three ways which would appear to solve the problem:
1. Get a bare thermistor with the same resistance and characteristic curve from Digi-Key, Jameco, etc., and use it instead of the stock part. Locate it in the incoming air stream so it is fast responding.
2. Build an airbox with an integrated air filter. I've seen photographs of this having been done, but it is a very time-consuming undertaking.
3. Revert to the stock airbox, possibly with modifications to streamline the sharp walls at the AFM connection, alter it to fit the Lexus AFM bolt pattern, and possibly modify it to increase the air intake opening by 50% to match the increased opening in the radiator bulkhead.
Any and all comments would be appreciated. Thanks.
BernieK
I'd like to know if anyone else has had this happen with an air cleaner located under the hood. I've got an HKS air cleaner (pretty far forward) because it appears to present the least impediment to airflow. Yeah, it does not clean the air very well, but I'm careful to drive where there is no construction dust, etc.
The air temperature thermistor is needed because the Karman Vortex AFM is a volumetric, not mass flow device, so it corrects for incoming air temperature. It is encapsulated by the plastic nub and possibly epoxy fill on the bottom of the Karman sensor. Thus it lags reading the true incoming air temperature. In the stock application this is of no concern, because air is always pulled in from in front of the radiator bulkhead. However, that is not true when air is taken from under the hood, particularly at low speeds, and particularly with the bottom engine cover in place.
There are three ways which would appear to solve the problem:
1. Get a bare thermistor with the same resistance and characteristic curve from Digi-Key, Jameco, etc., and use it instead of the stock part. Locate it in the incoming air stream so it is fast responding.
2. Build an airbox with an integrated air filter. I've seen photographs of this having been done, but it is a very time-consuming undertaking.
3. Revert to the stock airbox, possibly with modifications to streamline the sharp walls at the AFM connection, alter it to fit the Lexus AFM bolt pattern, and possibly modify it to increase the air intake opening by 50% to match the increased opening in the radiator bulkhead.
Any and all comments would be appreciated. Thanks.
BernieK
