1990 535i M30 running very rich

[TiagE39]

11/89 (MY1990) 535i M30. DME constantly running engine rich to the point where exhaust smells strongly of gas. Cold starts are rough, warm starts often much worse (lots of cranking and booting the throttle to get it running). MPG's are 13 at best but usually around 8 these days.

I've checked/replaced:

-Coolant Temp Sensor
-Air Flow Meter (rebuilt)
-Plugs
-Fuel Press. Regulator
-Changed out DME for a spare
-DME reset
-Running voltage is good
-Distrib cap is good (no marks, oxidation, not excessively worn)

I also have a new O2 sensor and TPS switch to go in but haven't yet. What else should I be considering? I have not been able to improve the issue in any significant way.

[dannyzabolotny]

Check your fuel pressure regulator, when they fail they'll cause a very rich running condition. TPS can also cause a problem if it's not adjusted correctly or not putting out the correct resistance, since the DME uses that to adjust the fueling for idle/driving/WOT.

[danespann]

See if the vacuum line for the fuel pressure regulator has fuel in it, or if the fuel pressure regulator has fuel coming out of there while the car is running with the vacuum line pulled off the fpr. Common for them to fail this way and result in quite the rich condition.

[TiagE39]

FPR is new. TPS will be next on the list.

[fo3]

Either you have leaking injectors or your AFM is at fault?
Time to start testing things rather than throw parts at it. What is your fuel pressure, do your injectors leak, have you tested the FPR?

If those are good then I say AFM is still bad.

Going through a parts list guessing O2 or TPS etc is wasting parts and money in my opinion. Test, check, double test/check.

[dannyzabolotny]

Yeah, I'd pick up a Bentley manual and get to work with a multimeter to check that all the sensors are within spec.

One other thing to check would be compression. I had an M20-powered E30 that came into my shop after several other shops did the parts cannon on it with a very similar issue: it was super rich on cold start and needed help to stay running, turns out it had very (evenly) low compression which was causing it to not burn all the fuel correctly.

[TiagE39]

it was super rich on cold start and needed help to stay running, turns out it had very (evenly) low compression which was causing it to not burn all the fuel correctly.

This is what I fear. Have bought a compression tester to verify.

[TiagE39]

I have not compression tested yet but I have noticed that the hard starting is not consistent. If the car has been sitting in my garage overnight it usually starts pretty normally and idles better. If compression were bad, wouldn't it be bad all the time?