Engine Rattle, Idle Problems & Loss Of Power

[race2win]

Hey guys, well I did some searching, but really didn't get a straight answer to my issues. If this has been covered many times in the past, my apologies in advance.

So here is the story....I've had my slick-top LSD 91 318i for a few months now & overall I really like it. It has been a great DD that is light on it's feet, gets good MPG, & has room for my kids. My only complaints is the typical M42 lack of horsepower (makes my bone-stock 94 Miata feel FAST ) & the following issues. The first issue is a loud rattling coming from the engine when it's cold. It comes & goes depending on RPM for about 5 minutes, then goes away when things warm up. There are less-loud rattles that happen all the time as well, but when it's cold it's LOUD. My first thought is timing chain...I've read up on all the issues these engines can have, but about a month ago I pulled my valve cover to inspect the chain, & from the top the chain & cam gears look fantastic (see pic). I also did the lower pan bolt inspection...no guide debris (or bolts) in the pan. Is this noise I'm hearing possibly the tensioner? Obviously I should take off the front cover & inspect it, but since the chain looked so good I don't want to go through the work if it's not neccessary.

My next issue is an intermittant surging idle & poor driveability. When the car is cold, it runs fantastic with good power & a steady idle (except the loud rattle listed above). After it warms up a bit it loses quite a bit of power & sometimes has a surging idle. It runs very smooth during this...it's not dropping a cylinder or anything...& it never dies when the idle is surging (goes from about 500-1200 RPM). It drives just like normal but feels like it's down about 20+ HP, like either the timing is off or like it's breathing through a straw.

Is the surging idle issue caused by the ICV or TPS? Could that also cause the power loss? The idle issue is fairly random, but the power loss happens every time I drive the car, so I'm thinking the issues are not linked. I replaced pretty much EVERY rubber hose under the intake a month ago or so, so many of the OEM ones were cracked & brittle I thought sure it would fix the issues I've been having...but no luck :confused:

Any help or ideas would be greatly appreciated! Thanks in advance!

[bmwman91]

Does the loss of power feel like serious bogging that suddenly goes away around 4000RPM? I am also having that behavior, and I have narrowed it down to either the air flow meter or the O2 sensor. Do you ever get a check engine light driving in heavy traffic?

[race2win]

No, the power loss is consistant across the rev band...it runs basically the same as when it's cold, only with much less power. Throughout all of this, no CEL has ever come one, & it passed the CA smog inspection last month the way it is. One of things I was thinking was possibly a clogged cat, & as it warmed up everything expanded in there restricting exhaust flow. I guess that still could be the problem, but I'm thinking it would not have passed the smog test if that were the case. My exhaust system is pretty ugly looking & needs replacement, as funds permit here in the near future I am planning to replace everything from the header flange-back, including a new high-flow cat. Maybe that will cure the power loss :confused:

Before buying this car, I drove another one, & from what I remember that one built more & more power as the revs climbed, all the way to redline. Mine feels much stronger than that car at lower revs (2500-5000) when it's cold but has always fallen pretty flat above 5K RPM. What's normal? A strong midrange but flat on top, or weak bottom end but pulling harder & harder all the way to redline (like most Hondas or Mazda Rotaries)?

[dinu.negrean]

I would check the fuel pressure. Had a similar case on an M42 that was not holding the pressure at high rpm.

[BlueBMW]

I wish my cam gears looked that good