SRR2
03-17-2005, 11:10 PM
I posted about this a few days ago and have done some work since then. Unfortunately, things are not going well.
This is a '89 535i manual trans, 115000 miles. Engine in excellent condition with lifetime Mobil-1. No oil burning at all. Operating temperature range is normal. Passes all emissions tests. When it's working normally, it's smooth as proverbial silk and gets ~27MPG in average usage.
To recap, during the power-down for battery replacement, the Motronic lost its adaptation. Ever since then it has been acting crazy. Idle wanders all over. Sometimes it's at 700 where it's very smooth and steady, and then when it acts up it ranges from 1000 to 2000+. The fuel cutoff at closed throttle operates intermittently. Occasionally closing the throttle over 1500 rpm the fuel cuts off as it's supposed to. Other times, like during shifting, releasing the throttle does nothing. If the engine ran up to 3000 in gear, it 'hangs' at that speed with the throttle closed. The mechanics of the throttle operate freely. No friction or hangup. When this happens the speed gradually returns to around 1000 rpm over a period of 10-15 seconds. As you might expect, driveability is horrendous.
Here's what I've tried so far: 1) inspected fusible links -- nothing found. 2) Removed idle control valve. Cleaned (wasn't very dirty) and electrical test. No problem found. 3) Checked operation of throttle position switch. Closes as required at closed throttle. Resistance of switch is low in closed position, infinite in open position. Voltages from ECU to the switch are correct. 4) Disconnected O2 sensor while engine cold. Erratic behavior was essentially unchanged as the engine warmed up. CEL set after about 15 minutes of driving. Reconnected O2 sensor and CEL cleared in a couple of minutes. Erratic idle/fuel cutoff continues as before. 5) I tried the conditioning technique I found on Shogun's web site. The gist of that is run the engine up to 5K in 1st, and let off the accelerator and let the car slow naturally to idle. Repeat at least two more times. Then let the car idle for at least 5 minutes. This might have made an improvement. 6) On inspecting the engine, some bad rubber has turned up. Minor cracks, not enough to significantly influence operation, which is consistent with the occasional perfect operation of the system.
And it gets worse! In the process of all this I discovered 1) a leaking radiator, and 2) a leaking power steering reservoir/hose.
AARGH.
Anyway, I'm still soliciting advice. I'm wondering if replacing the original ECU chip with one of these EAT chips would provide better adaptation behavior. The $200 for one of these would be a small price to pay if it would help clear this nonsense up. But I'm looking for any other good advice. The simple fact that occasionally it works perfectly is particularly frustrating. That tells me that the passive parts involved in operating the engine (things like hoses) are probably OK, and the problem is most likely in the vicinity of the ECU. Since the throttle mechanics work correctly, the only source of the high idle must be the idle control valve, and that part appears to work as advertised. So it's likely that it's being commanded to do the wrong thing. If I could single out one thing that appears to be the culprit, it's the adaptation algorithm which seems to tolerate ridiculous operating characteristics. (This why I'm thinking the EAT chip might be a viable solution.)
Oh, one more thing. For about 10 minutes this afternoon the engine was idling perfectly at 700rpm. Cycling the A/C compressor on and off made NO difference in engine speed, providing yet another confirmation that the ICV is working right.
I'd sure appreciate some wisdom here.
This is a '89 535i manual trans, 115000 miles. Engine in excellent condition with lifetime Mobil-1. No oil burning at all. Operating temperature range is normal. Passes all emissions tests. When it's working normally, it's smooth as proverbial silk and gets ~27MPG in average usage.
To recap, during the power-down for battery replacement, the Motronic lost its adaptation. Ever since then it has been acting crazy. Idle wanders all over. Sometimes it's at 700 where it's very smooth and steady, and then when it acts up it ranges from 1000 to 2000+. The fuel cutoff at closed throttle operates intermittently. Occasionally closing the throttle over 1500 rpm the fuel cuts off as it's supposed to. Other times, like during shifting, releasing the throttle does nothing. If the engine ran up to 3000 in gear, it 'hangs' at that speed with the throttle closed. The mechanics of the throttle operate freely. No friction or hangup. When this happens the speed gradually returns to around 1000 rpm over a period of 10-15 seconds. As you might expect, driveability is horrendous.
Here's what I've tried so far: 1) inspected fusible links -- nothing found. 2) Removed idle control valve. Cleaned (wasn't very dirty) and electrical test. No problem found. 3) Checked operation of throttle position switch. Closes as required at closed throttle. Resistance of switch is low in closed position, infinite in open position. Voltages from ECU to the switch are correct. 4) Disconnected O2 sensor while engine cold. Erratic behavior was essentially unchanged as the engine warmed up. CEL set after about 15 minutes of driving. Reconnected O2 sensor and CEL cleared in a couple of minutes. Erratic idle/fuel cutoff continues as before. 5) I tried the conditioning technique I found on Shogun's web site. The gist of that is run the engine up to 5K in 1st, and let off the accelerator and let the car slow naturally to idle. Repeat at least two more times. Then let the car idle for at least 5 minutes. This might have made an improvement. 6) On inspecting the engine, some bad rubber has turned up. Minor cracks, not enough to significantly influence operation, which is consistent with the occasional perfect operation of the system.
And it gets worse! In the process of all this I discovered 1) a leaking radiator, and 2) a leaking power steering reservoir/hose.
AARGH.
Anyway, I'm still soliciting advice. I'm wondering if replacing the original ECU chip with one of these EAT chips would provide better adaptation behavior. The $200 for one of these would be a small price to pay if it would help clear this nonsense up. But I'm looking for any other good advice. The simple fact that occasionally it works perfectly is particularly frustrating. That tells me that the passive parts involved in operating the engine (things like hoses) are probably OK, and the problem is most likely in the vicinity of the ECU. Since the throttle mechanics work correctly, the only source of the high idle must be the idle control valve, and that part appears to work as advertised. So it's likely that it's being commanded to do the wrong thing. If I could single out one thing that appears to be the culprit, it's the adaptation algorithm which seems to tolerate ridiculous operating characteristics. (This why I'm thinking the EAT chip might be a viable solution.)
Oh, one more thing. For about 10 minutes this afternoon the engine was idling perfectly at 700rpm. Cycling the A/C compressor on and off made NO difference in engine speed, providing yet another confirmation that the ICV is working right.
I'd sure appreciate some wisdom here.