Help! Erratic Idle And Dies! Vacuum Leak Or Something Else???

[scott-superman]

I HAVE A 1987 325i THAT I JUST SWAPPED ENGINES IN (THE GUY I BOUGHT THE CAR FROM KNOCKED A HOLE IN OIL PAN AND BURNED UP THE BEARINGS/CRANK).

WITH EVERYTHING HOOKED UP, THE ENGINE SPEED JUMPS UP AND DOWN A FEW TIMES UNTIL IT DIES. IF I GIVE IT SOME THROTTLE, THEN I CAN KEEP IT GOING AND IT SEEMS TO SMOOTH OUT FOR THE MOST PART. IT RUNS/DRIVES FINE AT ANYTHING EXCEPT IDLE. HAS A SLIGHT HESITATION SIMILAR TO A BAD ACCELERATOR PUMP ON AN A CARBEURATED VEHICLE.

IF I DISCONNECT THE CONNECTOR FROM THE AIR FLOW METER THEN IT IDLES GREAT, BUT IT IS NOT DRIVEABLE AND BOGS DOWN WHEN YOU TRY TO ACCELERATE.

IT SEEMS LIKE IT COULD BE A VACUUM LEAK. IF SO, WHERE ARE SOME OF THE LIKELY PLACES AND HOW DO I GO ABOUT FINDING IT/THEM???

THANKS SO MUCH FOR YOUR ASSISTANCE!

 

[f1racer77]

Your assumption of a vacuum leak is right on! Although, I would check the idle control valve. This is most likely the problem. If that isn't it, its probably a vacuum leak.

 

[epj3]

A LOT of times the intake boot goes bad (happened to my car). I replaced it and that fixed it. I have one for sale on ebay right now that should work on your car (Parting my car out since i was recently in an accident).

Hope you get it fixed!

f1racer77 - An idle control valve wont actually mess up the idle like he's talking about. It'll just make it not idle as smoothly as it should.

 

[scott-superman]

Dear f1racer,

Thanks for input. I used WD 40 and starting fluid to spray around vacuum hoses and got no rise in rpm, so even though the intake boot is old and cracking I don't think that is my problem.

I am running through the checks on the idle air stabilizer valve.

1) With engine running, disconnect the electrical connector from the valve. The idle speed should increase to about 2000 rpm. I got no increase. That's bad!

2) If it does not increase, then turn off the engine, unplug the connector and check resistance between outside terminals and inside to outsides (40 and 20 respectively). That's good!

3) If idle air stabilizer valve fails any of the tests, then replace it with a new one.

4) I also checked the supply voltage on the center pin of the connector and it was 10.5. That's good!

I think I will replace this valve from my tests so far.

Any additional input is appreciated!

Thanks for your help!

 

[scott-superman]

Hello epj3,

Thanks for input! Sorry to hear about your accident. What was your car? Are the seats good? What about glove compartment and/or dash? Please see my reply to f1racer77.

Would you sell this idle air stabilizer valve too?

I'll check out your auction. They are available pretty inexpensively new from the parts bin.

Thanks again!