SRR2
03-29-2005, 05:32 PM
To recap: '89 535i manual. 150000mi. Changed battery and immediately ran into idle and fuel cutoff problem. Idle is often too high, usually in the range of 1000 rpm. When it's in the state of misbehavior characterized by the high idle, the fuel won't cut off above 1500rpm like it's supposed to. Take your foot off the accelerator and it continues to feed fuel at a rate that almost prevents deceleration. The ECU isn't throwing off any "stomp" codes. No CEL. I cleaned the ICV and got a small improvement (the idle was a little better controlled) and then replaced it with a new one. Problem persists. At the same time, I replaced some old rubber in the vicinity of intake and breather. I checked the fusible links. The O2 sensor seems to be working, as the problem persists virtually the same way with (no CEL) and without (CEL on) the sensor connected, and when the engine is cold (when the sensor isn't used). Water temp sensor is in spec. Throttle position sensor switch is functional and has voltage. I have reset the ECU too many times to count. I've tried the ECU calibration procedure (posted by Shogun) many times without improvement. Something is causing the ECU to supply fuel when it shouldn't, particularly above the 1500rpm closed-throttle cutoff point.
Now I'm a little suspicious of the AFM. When I had the rubber off to replace it, I tested the temperature sensor (in spec) and measured the resistance between pins 2-3 as the Bentley manual describes. Bentley is not particularly helpful in determining operation because they say something like "the resistance should vary". Well thanks a lot. Vary HOW? And here's why I'm suspicious: With the vane closed I get 550 ohms consistently. As the vane opens the resistance rises to almost 900 ohms in the center of its travel, and then as it approaches full open, the resistance drops again to around 400 ohms. That doesn't make a heck of a lot of sense to me. I'd expect it to increase or decrease as it traverses, but not rise and then fall again.
Does ANYONE have some spec on resistance v. travel?
And while I'm at it, can this be converted to a hot wire or other less restrictive MAF sensor? If I'm going to have to replace it, I'd like to use better technology.
One other observation... The bad behavior is predictable. On a warm start the engine is perfectly controlled at idle, while delivering power, and during deceleration when the fuel cuts off as it should. After about two to three minutes, the bizarre stuff starts. This happens every time. Then, when it's misbehaving, I can come to a stop and watch the idle sit at 1000 rpm. After a predictable two minutes, the idle drops to exactly 700 rpm where it will sit indefinitely. The 700 rpm idle is smooth. Plus, I can cycle the A/C compessor and it doesn't move at all.
This is driving me crazy. I hope someone can help me out here. At this point I'm seriously considering taking it into the dealer, even at the risk of them engaging in an expensive Parts Replacement Guessing Festival.
Now I'm a little suspicious of the AFM. When I had the rubber off to replace it, I tested the temperature sensor (in spec) and measured the resistance between pins 2-3 as the Bentley manual describes. Bentley is not particularly helpful in determining operation because they say something like "the resistance should vary". Well thanks a lot. Vary HOW? And here's why I'm suspicious: With the vane closed I get 550 ohms consistently. As the vane opens the resistance rises to almost 900 ohms in the center of its travel, and then as it approaches full open, the resistance drops again to around 400 ohms. That doesn't make a heck of a lot of sense to me. I'd expect it to increase or decrease as it traverses, but not rise and then fall again.
Does ANYONE have some spec on resistance v. travel?
And while I'm at it, can this be converted to a hot wire or other less restrictive MAF sensor? If I'm going to have to replace it, I'd like to use better technology.
One other observation... The bad behavior is predictable. On a warm start the engine is perfectly controlled at idle, while delivering power, and during deceleration when the fuel cuts off as it should. After about two to three minutes, the bizarre stuff starts. This happens every time. Then, when it's misbehaving, I can come to a stop and watch the idle sit at 1000 rpm. After a predictable two minutes, the idle drops to exactly 700 rpm where it will sit indefinitely. The 700 rpm idle is smooth. Plus, I can cycle the A/C compessor and it doesn't move at all.
This is driving me crazy. I hope someone can help me out here. At this point I'm seriously considering taking it into the dealer, even at the risk of them engaging in an expensive Parts Replacement Guessing Festival.