This is a posting to go along with Monte's concerning crankcase ventilation. This past weekend I finally got around to cleaning the throttle body on my '88 740T that has been idling unsteadily. The throttle body was gross which is not surprising since I doubt the P.O. ever had it serviced. A good cleaning, new gaskets, and new o-ring, and the engine idles like a dream. Never thought I'd see this engine idle this smooth.

While the throttle body was off, I attacked the crankcase ventilation system. I have been experiencing a bad oil leak from the o-ring at the bottom of the turbo oil return pipe. Oil consumption has been 300 - 450 miles per quart. I don't think the engine is burning oil since there is no smoke, the new exhaust system (last spring) is not overly carboned up, the spark plugs when replaced last summer showed no sign of fouling (just the typical yellowish deposits), and minimal oil coating in the intercooler and associated plumbing. Besides, I can see the oil dripping from the block near the turbo oil return pipe with the engine running. In addition, I performed the "oil cap jiggle test" a few weeks ago and there was a definite jiggle. Going after the "flame trap" and breather box is much easier with the throttle body off.

I did not find any of the passages or hoses in the vent system plugged. I cleaned out all the passages anyway on the throttle body, intake manifold, and flame trap housing. I removed the breather box only to find out it is a sealed unit. I was able to blow air through all the ports, so I concluded that it was not plugged. When reassembling the vent system and throttle body, I replaced most of the vac. hoses since they were old, hard, and/or disintergrating.

The oil filler cap still jiggles at idle. Though when I go to lift the cap off, I feel a slight suction which I can't remember existed before. Apparently there is still a pressure pulse in the crankcase that is causing the cap to jiggle. Time will tell whether or not the crankcase ventilation is improved. Reduced oil leakage will probably be the best indictor.

My questions to the gurus out there are:

1. How much suction should I expect with the vent system working properly? Should the oil cap suck down hard, or is a slight jiggle with what appears as an overall suction enough?

2. Did I miss anything when servicing the throttle body and vent system? Anything else cause a crankcase vent problem that I missed? I thought of bad rings as a possibility, but wouldn't see more evidence of burning oil?

Thanks,

Gary DiFrancesco