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rough idle, no start 700 1991

posted by  josed on  Wed Oct 22 22:13 CST 2003
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Hi all, have enjoyed reading and learning from your posts all these years. I have a problem that's kicking my b*@@.

I have a 1991 740 B230 Rex Regina with 139k. For a while now, in hot weather, the car won't start after it's been driven for a while. I also have been getting a diagnostic code "2-2-3" - missing IACV signal. The kicker is, the IACV checks out using the diagnostic, and the resistance at pins 9 & 33 of the FI ECU is 4.5 ohms - it checks out (according to my Haynes book). Previous posts say to checkout the IACV, RPM sensor and maybe power stage.

The car also has been idling roughly lately. Not like it's running on 3 cylinders, but the car vibrates a lot and doesn't have the oomph it used to. The entire car vibrates, but it isn't a steering or wheel problem. Twice in 6 days, the car hasn't started when cold - and I drive it everyday. It seems to have started after I pull out and replace all the plug wires, FI wires, coil wires, power stage wires.

The RPM sensor lead insulation is falling apart, so I will replace it. This may be a contributor.

Finally, I was checking the coil and power stage when the resistance of the power stage wasn't checking out. The "B" plug on the 2-prong side should be reading zero ohms to ground but it reads 1.7ohms. The coil checks out.

My question: Sounds like the power stage is at fault. But, would that correct the vibration/rough idle and the 2-2-3 code? I can kind of see it, but then again I can't - inconsistent signal to the coil from power stage could cause spark/fuel timing problems thus vibration. Maybe the ECU is trying to compensate with the IACV (?) and it can't (signal is going out of range (?)) thus generating an error.

BTW, I changed out the plugs, plug wires, and coil wire. Fuel pump, FI Relay, RS Relay checked out. I'm confident I don't have a fuel problem.

What I know I've gleaned from here, so I only know enough to be dangerous. Since I need my car on Friday, I guess I'll just buy a Power Stage and RPM sensor. If that doesn't work, then changeout the distributor cap? I haven't gone under the car to check engine mounts - as you can see, I'm all over the place right now. Thanks






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