Help me Diagnose my 525i

[lewisds]

**** Problem Solved ****

The problem has been resolved - there is a 24 x 3.5mm O-ring that attaches to the underside of the intake manifold, where one of the tubes from the ICV attaches. The original O-ring was in such bad shape that it disintegrated when I pulled everything apart. I replaced the O-ring, and the car runs wonderfully now.


I have a 1993 525i with the M50TU engine / Automatic transmission.

This started as a misfire, so I replaced a bad ignition coil that had melted. I later found out that the DME was toast, so replaced that with a working model. All cylinders now fire as expected.

After doing some research on this forum, as well as some other e34 sites, I have proceeded with the following:
-Removed, cleaned, and replaced the ICV
-Removed, cleaned, and replaced the MAF assembly.
-Replaced the intake tube (between MAF and Throttle Body), as it had 2 cracks on the bottom ports, and several smaller cracks in the bellows.

Here are the symptoms:
-If I jam on the gas pedal, the car sputters before getting up to about 2k RPMs. above 2k RPMs, it behaves just fine.
-If I unplug the MAF, it improves SLIGHTLY. Once the car is warm, it doesn't seem to matter if the MAF is plugged in or not.
-If I drive around in lower gear, and keep the RPMs up, it seems to improve as time goes on (and the engine warms up).
-If I hit a stop light, the engine has a bit of a searching idle, and all of the lights dim. It feels like it is just on the edge of stalling.
-There is a hissing noise that seems to be coming from just underneath the intake manifold (where the intake mani bolts to the block). I can't find any vacuum leaks underneath it - this may just be the sound of engine, but it seems unusual to me.

Thanks in advance for any help you guys can offer.

[GumbysE34]

Lots of good questions here, as well as a good start as far as the procedure followed to improve the running conditions of the engine.

I'm sure some E34 gurus will jump in here soon with some info!

[Steve547i]

I had the melted coilpack/misfire/ecu issue too. It was sucha pain diagnosing. It sounds like vacuum leaks are still an issue. Check every single rubber hose. And possibly, and I know its on my list, intake manifold gasket.

[E34ührer]

Or the intake boot. I had one a while back that was cracked...you couldn't tell, but replacing it solved a TON of issues.

[darrenforeal]

Did you check the injectors, sparks and fuel pump? Next I would check the VANOS. But I could be WAY off, and there are guys on here that know a great deal more than me. Hopefully they will chime in.

[lewisds]

Steve92e34 – I was hoping to avoid the replacing the intake manifold gaskets (all 6 of ‘em), but that may be the cause.
MeanM50 – Already replaced the intake boot, didn’t seem to help at all.
Darrenforreal – Spark is good on all 6 cylinders. I have not checked injectors. I can’t imagine it being the fuel pump, as the car seems to run fairly decently in the higher range. Also, how would I go about checking the VANOS?

Thanks,

[Somethingelse]

It sounds like a vacuum leak to me. Did you check for vacuum leaks by spraying carburetor cleaner at different connections? I'd spray around while engine is on and see if there is a change in idle speed. Pretty new to the e34 but I would suspect gasket at throttle body/intake manifold, intake manifold or maybe a vacuum hose disconnected somewhere.

[lewisds]

The problem has been resolved - there is a 24 x 3.5mm O-ring that attaches to the underside of the intake manifold, where one of the tubes from the ICV attaches. The original O-ring was in such bad shape that it disintegrated when I pulled everything apart. I replaced the O-ring, and the car runs wonderfully now.

[KarmaRockuz1]

nice. my 95 525i is experiencing some of these issues.. i replaced 2 hoses and will check for more vaccum leaks..
Lewisds, can you tell me how you went about replacing the o ring and pin pointing the problem? thanks

Also where is the icv and how should i clean it? thanks