I just picked up a 1993 525i E34 Auto with single Vanos (first year), no engine codes or warning lights other than brake pads wear. The engine compartment looks clean, no random oil spurts, or liquids. No knocking or tapping, not overheating, nothing I can put my finger on other than an odd drone and wind noise at highway speeds (guessing rear diff needs lube) . The CATs were clogged and got replaced, there are a couple of exhaust leaks from the muffler and a couple of bullet holes ( :| dont ask)

I am having a significant problem with stumbling at idle & acceleration. Freshly recharged the AC and the problem is much worse with the A/C on. Seems go fine at highway speeds but still takes a while to pick up speed to pass someone.

It revs very poorly and seems to top off around 2200RPM - no idea why unless the exhaust route past the cats is also clogged.

What I have done:

- TPS
- MAF
- Intake boot, housing, air filter
- CAT$$$
- Throttle Body clean
- Seafoam engine
- Battery

After doing this the idle has improved but it still seems to go through a cycle of idling well, then stumbling, then running well for a while.

What I have not done:

- O2 Sensor ?
- Injectors ?
- Plugs/wires/coils ?
- Fuel filter/Fuel lines/Fuel Pump ?
- Tranny flush / rebuild (heaven forbid) ?

I am somewhat at a loss and really dont want to buy an electrical part I wont be able to take back if I dont need it. Has anyone experienced this ? Any pointers of where to look next ?

 

Have you pulled the plugs or cleaned the IAC?

 

It will only rev to 2200? Cats go bad when the engine is running poorly. A restriction in the exhaust system would constantly cause a loss of power.

Is the AC system charged to the proper level? If the AC compressor is locking up or overcharged it can put a large strain on the engine. I have seen bad compressors stall engines.

Tune it up. That should be the first step.

 

Just pulled the plugs yesterday - the special dude before put in non-matching AutoLites.. replaced with BMW recommended Bosch. Seemed to help a bit - but noticed that there are 3 diff brands of coils on there as well... the fun continues.

 

The CATS were clogged and I have the new CATs and the O2 sensor on there now. The AC system was discharged and refilled professionally - it now blows rather cold.

 

Thank you guys for good replies, I decided to check everything else out as well and noticed a small amount of coolant right under the fan clutch area... I was planning to check the timing belt/chain anyhow. Popped off the valve cover and had a fun 6 hrs with a new timing chain, new tensioner, new water pump, new thermostat and a set of ridiculously expensive special order BMW gaskets which I have to wait on from BAP.

I love working on old Imports !