Question
Little tube looking ob
QUESTION: I have a 1997 X3 SOHC Excel and it is surging every now and then or has what feels like a flat spot in the throttle. It also would intermittently not start. You could wind it over sometimes for 1 1/2 hours and it wouldnt start and then go back an hour later and.... hey hey, no problem! But we think we have fixed that. Touchwood! Faulty crank angle sensor. The surging however, that I thought might be related to the starting issue is still bugging me. Seems to only do it at temprature and at random. However i can generally get it to do it on demand to show someone what i'm talking about by sitting on 110km/h for a short time and then just inching the throttle slightly. Heres the catch..... we have replaced fuel pump, fuel filter, coil pack, leads, plugs and crank angle sensor. I'm all out of ideas. Could it actually be the transmission itself surging because when i drive to work in the morning (approx 22km) it seems to take a long time (about 10-12km) for the transmission to drop into the final drive ie overdrive. Also, is the little tube looking object attatched to the throttle body related to the transmission at all (see picture) ie auto trans vaccumm equipment.
ANSWER: Hi, Travis. The number one thing I'd be checking in this case is the signal from the throttle position sensor. Ideally, this is done with a scan tool that will read the data stream from the car. Next, I'd manipulate the throttle in the way you describe that makes the problem occur and see whether the throttle opening reading on the scan tool corresponds properly to what is occurring on the car. If not, there is likely a problem with the throttle position sensor or the contact in the connector for the sensor.
It's unlikely this is caused by the transmission, especially if you can get it to occur when the transmission is in neutral or park, but the overdrive problem you describe can indicate a serious transmission issue nonetheless.
The device you've pictured is the idle actuator. It has nothing to do with the transmission, but can, much less frequently, also cause surging issues if it sticks. If you're able to get the engine to surge when the car is idling in neutral or park, give the actuator a light whack with a medium-sized wrench. If that causes the engine to return to normal idle, the actuator is sticking.
---------- FOLLOW-UP ----------
QUESTION: This morning on the way to work and several times in the past, when the car has surged it has caused the transmission to drop back a gear. Could there be something wrong with a gearbox sensor ie kickback sensor or solenoids etc etc. I have a new TPS coming in mail, should be here in a day or two. If that doesn't fix it, COULD it be a transmission sensor and which one would be most likely.
AnswerThis isn't likely to be a solenoid issue unless you have some sort of solenoid or incorrect gear ratio stored.
There is no "kickback" sensor. The transmission control module (TCM) determines the proper gear for the transmission via engine speed, vehicle speed, input shaft speed, output shaft speed, throttle angle, and calculated engine load.
Does your check engine lamp illuminate when the transmission drops back a gear? If so, the TCM is indicating that it has seen something abnormal. In this case, check the diagnostic trouble codes stored in the TCM and engine control module (ECM).
