Still having high RPM and idle problems...

[paanta]

I feel like a damn broken record here. Sorry to keep posting about this problem... Car in question is a '91 535i. I'm an engineer by training, have owned a dozen or more Bosch fuel injected cars, and haven't visited a pro mechanic in 10 years....and still this is leaving me completely stumped. I need input from the Gurus.

Symtoms:

• Idles rough after warm start (car sits for 10 minutes to ~3 hours). Cold start idle is great. Restarting a hot car immediately is great.
• No power for ~30 seconds after warm start. Throttle input causes engine to bog down. Car will barely move. Revving over 2500-3000 rpm clears it up a little.
• Won't rev past 5800 rpm or so. Cutoff is immediate and feels exactly like a rev limiter. Holding WOT in 2nd gear the car will sit right on 5800 rpm and not go over. Doesn't feel like wheezing out of breath as with a fuel pump problem.
• Normal otherwise. Tons of power between 3K-5K, sounds good, idles perfectly, good throttle response and it starts on the first crank every time.
• Intermittent Error 1222. Lambda rich/lean control stop. CEL flashes on sometimes during bad idle. Seems better after O2 replacement, but persists nonetheless.

Tests:

• Crankshaft Position Sensor: Replaced with non-OEM, but no difference. Resistance is fine. Air gap on loose side, but within, spec.
• Coil: Replaced. Did nothing. Returned part.
• Plug wires: Replaced
• Distributer+rotor: Look fine
• Plugs: Haven't checked...seems unlikely culprit. Still, check this weekend
• Alternator+Battery: 12.3v car off, 13.78v measured between jump start terminal and engine ground. Constant with RPM and only slight dip with larger power draw. Borderline low?
• Throttle Position Sensor Tested and good. Unplugging at idle causes instant bad idle.
• AFM: Cleaned (plate was sticking a bit), resistance of wiper smoothly goes from 500->1100 ohm and then back down to 800 with door fully open.
• Idle Stabilization Valve: Cleaned. Makes a sound when shaken. 20/20/40 ohms. Not much difference when connector unplugged though...
• Air temp sensor: Air temp sensor reads normal.
• Coolant temp sensor: Tested OK
• Oxygen sensor: Tested OK. Replaced anyway. Old one had whitish deposits on it (previous owner replaced cyl head after gasket failure)
• Fuel pressure : 3.0 bar with pump running, engine off. 4.5 bar if return line pinched. 2.5 bar with engine running, up to 3 bar with throttle input.
• Fuel flow: 0.9 quarts after 30 seconds. Bentley calls for 0.93. 3% low enough to matter if pressure tests OK?
• Fuel Pressure Regulator: Replaced. No difference.
• DME: Replaced. Symptoms persist. New DME seems to cause car to idle high (1100 rpm at times) though it has stock chip vs. EAT.
• Vacuum leaks: Cracking oil cap causes instant bad idle. Spraying carb cleaner all over causes no idle fluctuation
• Tachometer: Tested against hand held tach. Works fine.
• Fuel filter: Replaced

Thoughts....

• Are the two problems (rev limit and bad warm starts) related?
• The car runs fine most of the time, and the cutoff at high RPM is VERY sudden, so I don't think fuel pressure/flow is a problem.
• Bentley's Bosch fuel injection book says Bosch defines the warmup stage as from the end of cranking for about 30 seconds. This coincides with by bad running. Maybe it's mistakenly thinking the car is starting cold when it's really starting warm and giving _way_ too much enrichment. Or maybe it thinks it's starting hot and is giving not enough enrichment. Air temp sensors are fine at the sensor itself, but perhaps the wiring to the DME is bad, causing higher resistance, which makes the sensor read low?
• The stomp test works, but it seems intermittent. I have to try 5 or six times to get it to cause the CEL to flash. Throttle switch works when tested at the switch, but again, maybe the wiring to the DME is bad?
• If the car wasn't seeing WOT because of a flaky throttle switch, would it still pull to red line?
• How sensitive is the CPS to the air gap? Mine is on the loose side of spec.
• Mark D'Sylva said a bad wheel speed sensor can keep the car from revving past 6K. Is this true on my old 535i with no traction control?

Next steps...

• Start checking sensor values from the DME side?
• Check and gap plugs, just for the hell of it.
• Double check all grounds.
• Others?...