My dad's 1990 535i (160.000 miles) has been having problems with running and idle. Initially, the engine would just bog down at idle. That was normal when we would, for instance, stop at a stoplight after the engine has been warmed up and been running for a while. It would almost sound like we were running on 5 cylinders. If we gave it some gas the engine would speed up like normal. After a few years the car is now inoperable; it will start up and run for a few minutes and slowly die. If the accelerator is depressed, it will die. The OBD code is 1222 (I believe), equivocating to a mixture too lean or too rich. We have slowly been trying to repair it when time and money allow: New Oxygen Sensor New Fuel Filter New Distributor Cap and Ignition Rotor (fried) Replaced a vacuum line (apparently had been cracked for some years; didn't fix problem) New Radiator, Hoses, Belts, Water Pump and Thermostat (as they were needed regardless) Does anyone have thoughts on what/where/how to start inspecting next? Also: Air filter, oil filter and oil have always been changed so that's not the problem. I am about to adjust the valves as I don't believe they have been adjusted for years(!) Thank you, Bob Balfany
A few things to check. Off Idle switch. (replace) MAF wire might be worn or out of cal. (Can be rebuilt or calibrated) With 160k, fuel Injectors can become clogged and cause problems. There are places that can test and rebuild them for $30-$40ea. which is way less than buying new. Perhaps not the single problem, but check the plug wires, if original, they could certainly have developed cracks and cause a miss. (replace) Try cleaning the throttle body as it can become gummed up where the butterfly sits at rest blocking airflow and causing poor idle and rich condition. There are spray cleaners that will dissolve the build-up, but additional scrubbing with a soft toothbrush and cotton rags will provid the best result. Hold the butterfly wide open to gain full access. Get the Throttle Body cleaner that is safe for "coated" TB's or you could remove protective coatings. This will, if it is clogged, provide a much improved idle and perhaps lean out the mixture a bit. I may be missing something simple, but hopefully I have given you a few items to check. Perhaps others will add additional items to check.
It has a vane airflow meter, not a hot wire MAF. This component is suspect, and if you can find someone that has one, you can swap test it and see if it runs any better. Everything else DJ mentioned should be checked, but it would be a good idea to know if it runs rich or lean. If lean, then spritzing a little carb cleaner into the intake should make it run better. If rich, then that would make it worse. Were any plugs black? Have you checked it for a vacuum leak other than replacing that hose?
Paul, Didn't realize it was a vane airflow. Should have known... You are certainly right about it be suspect. The one on my old, now sold, 85 325e went bad and displayed some of the same symptoms and additionally caused surging on acceleration.
True, this is a possibility. Check fuel pressure if you can. Though, I have not seen one that will run OK when revved but poorly at idle when the fuel pump is dying because normally it won't flow enough fuel. Doesn't mean that can't be it, though.
Well it wasn't the Air Flow Sensor, I figured that out this weekend. Nor was the throttle body gummed up. The spark plugs were black, so it's running very rich! Spark plug wires are fine. I never got to testing the fuel injectors, idle air stabilizer, or throttle position sensor (I don't believe the car has traction control).
There are only a few common things that can cause a BMW of that vintage to run too rich. Coolant temp sensor (test it per the Bentley manual,) fuel pressure regulator, AFM (a swap test would rule that out befause otherwise this is impossible to test,) or one/both banks of injectors hanging open (bad ECU or short to ground in the harness.) If it is not one of those things, then it is an uncommon thing that requires more digging. Were all the plugs black?
It has one, and you should test it per the manual, because if it is sending the full throttle signal to the ECU, it will ignore the O2 sensor and will run a bit rich. This is not a common cause for problems on the big 6, but granthr is right, you should check everything that can be a possible cause.
Yes all of the plugs were black. I tested the AFM by the Bentley Manual and it operated as the manual said it should. But you say you can only test it by replacing it with one that is operable; that's a problem for us because we live in rural Minnesota. I have an E30 325i (1990), and my dad also has a 1981 528i. Is it possible to temporarily replace the AFM with one from the other two cars?
Well we figured it out- the distributor cap and ignition rotor were fried! Inside the cap were fragments and powder of oxidized metal. Now the car's running strong besides needing new spark plugs and fan clutch.
