Engine running rough and shaking badly at idle and at higher rpm too, hot /cold
Hi there,
My 93 525i was running great all year long before. Saturday night after dinner 50 miles away, started the car to go back home. Obvious rough running and engine making the entire car shaking, but no Check Engine Light (CEL) signal. Once engine hot, no change, while driving it was quite less powerfull and I could hear it and feel it strugle under the gas pedal when accelerating, like if it was missing on some cylinders (but I never experienced that so hard to tell now).
It ran bad like that but I drove it home 50 miles without other problems. On next morning I checked with my Peake tool to see if codes were stored and no codes. I confirmed with the pedal stump test and only code 1444 shows continuously = no codes. Started the engine and it was still shaking badly and running rough. Let it warm up a few minutes and checked by hand that all 6 exhaust ports were as hot one compared to each other, and all 6 were very hot, no difference between any.
I stopped the engine, removed the fan clutch to see if it was the problem and no, same behaviour without the fan clutch. Then I removed both belts, started again the engine and no difference, so it doesn't look like it is something driven by the accessory belts.
I disconnected the MAF socket and started the engine again, the CEL signal appeared right away, but otherwise no difference, still running bad and shaking. Then I repluged the MAF and checked that every vacuum hose was correctly set and everything was where it should be and no worn broken hoses were seen.
In the 4 last years, all vacuum hoses, intake manifold gaskets, throttle body gasket, MAF, O2 senson, coolant temp sensor, idle speed control valve (ICV), spark plugs were replaced. Passed smog test 3 years ago too in California. Also 3 years ago fuel pump with fuel level sender, fuel pressure regulator, fuel pump relay and fuel filter were replaced after fuel level sender failure. This year I replaced the vanos piston seal along with diaphragm spring upgrade on the intake camshaft, valve cover gasket, lower timing chain tensionner, engine doesn't burn any oil and was running great but pinging under load. This summer I also tested compression and each cylinder was at 160 psi, spark plugs were clean. One month ago I decarbonized the combustion chamber to some extent that it doesn't ping anymore, with Seafoam added by the small vacuum hose from the PCV valve. Fumigated the entire neighboorhood by doing that. Battery is 3 year old and seems fine, alternator was rebuilded this summer.
I searched a lot here and on bimmerboard to find insights to what could be wrong now. Most posts say either MAF or ICV or CPS, or fuel related, or coils and spark related. I doubt that MAF, ICV, or fuel related part is wrong because those were replaced recently and with a bad CPS the car should not start at all. Also again, there are no CEL warning.
Next Saturday I'll look at the spark plugs first, maybe test the coils. I read that it is possible that the ICV could block 'mechanically' and that would not be seen by the OBC. I also read a post from a guy that had a broken intake valve and the simptoms were kind of similar to mine. I will see that when I check at the spark plugs I guess it will be obvious on the plug, if not a compression test will tell me.
Any other ideas from the mechanical gurus here?
Thanks, Alex
525i 1993 (built 05), M50TU, auto, 231k miles
1993 (build 93/05) 525i automatic M50TU (vanos) 263K miles (ca. 423000 km) in Montreal, Canada (bought the car 9 years ago in San Diego, CA)