Slight mis-fire at partial throttle...until I disconnect air temperature sensor

Hi,

As I always write: I do not trust MPS outside the 70s production. I have seen brand new MPS from Mercedes from 2000s that did neither work properly nor could I make them work properly. It was simply scrap as the parts used to assemble it did not match. Poor quality control after serial production in 70s I am afraid.

Hi, yesterday I had the same problem on my BMW 3.0 CSi, and I temporary solved it by disconnecting the air temperature sensor in order to continue my trip. Did anyone (who had this problem) test the coolant temperature sensor? Unfortunately, in theese days I cannot make that simple test.

Could this problem be due to a grounded coolant temperature sensor (0 Ohm between the two pins at any engine coolant temperature)?

A grounded coolant temperature sensor entails a lean air-to-fuel mixture. Could it be roughly compensated by disconnecting the air temperature sensor (which entails a richer mixture)?

I made various tests, including the use of another ECU and another air temperature sensor. All sensors, together with that of engine coolant, seems to work properly within their operative range. With both the ECUs tested I saw the engine working with a lean mixture when the external air temperature raises over 30 °C. The problem is more evident at higher temperatures. In that condition, by disconnecting the air temperature sensor the problem is solved instantly gaining that seems to be (I have not a CO measurement sensor) a perfect drivability, without part-load hesitation and good high revs response.
With both ECUs, the problem seems to reduce gradually up to disappear completely as the external air temperature reduces below 24 °C. In that condition disconnecting the inlet air temperature sensor semms to have not a noticeable effect (sorry, I cannot make a rigorous measurement without having an exhaust gas analyser).

MAP sensor replaced with a new one acquired directly from Bosch some year ago.
TPS sensor renewed/rebuilt with new electrical contact.
Trigger contacts renewed/rebuilt.
New coil, new spark plugs, new cap, new wires etc., new condenser... Dwell and spark advance are ok. Fuel pressure regulator has been tested and it is ok too (2.1-2.2 bar).

Hi,

removing air temp sensor is not a recommended action. Why?

• Air Temp sensor is there to compensate air mass. Cold air has higher mass than hot air. That needs more or less fuel.
• Removing air temp sensor typically increases fuel by 20% in all situations - If you consider fuel a cheap resource you can do that. If not it is a bad idea

I would definitely recommend that you find your engine mechanics, ignition and other D-Jetronic issues instead of doing this kind of bricolage . If you still consider it a good idea, why not remove engine temp sensor? It enriches fuel mixture much more than removing air temp sensor.

My air temperature sensor is working its place and I never considered to disconnect it, with the exception of a brief temporary test.

I wrote that posts just to share my problem, hoping that someone who experienced a similar matter could suggest the way to fix it. It should be clear...

Hi,

then I misunderstood you that you would want to keep that sensor off permanently.