91 525i Wants to start but refuses too

I agree. The only two times my cars couldnt hold an idle at all:
350Z: forgot to reconnect the vacuum line on the intake tube = massive vacuum leak/no pressure built
E28: forgot to put the oil cap back on = massive vacuum leak/no pressure built

Both acted the same way as your car does. And one is 12 years newer and the other 5 years older!!!

Sent from Joe's Galaxy Tab 2 via BimmerApp

The only thing I have left to check is the ICV... All of the Vacuum lines are good, connected, and clamped down...

If you could perform a smoke test, do it to verify that you don't have any leaks.

Today I will be working on the vehicle so I will do a smoke test and confirm that I don't have a vacuum leak. Then I will test the ICV as told by many on here.

If I stopper up and unplug the ICV, would the engine still start?

Ok, so i just reread this whole thread to re-familiarize myself. As you'll be with the car today, please do stay online and keep us posted. We are your salvation. I'd also like to rattle off all of my theories, hear them out and take them into deep consideration.

• when listing MAF, you say good. Did you check the the resistance of it? could you remove it and clean it with a tiny bit of carb cleaner, or i believe they make MAF cleaner now...
• You end the "air" category with "yadayadayadayadayada"; that yadayadayadayada will be whats causing your car to behave this way potentionally. thorough thorough thorough.
• be very gently with ICV as the valve itself is rather fragile
• You said you did a compression test and all numbers were within a good running range, no need for that cylinder wash. UNLESS: cranking without firing has cause the fuel injected to eat the oil helping to seal the rings.
• Please do check Throttle position sensor for the hell of it. I'd like that peace of mind.
• Have you tried "manually" controlling your idle by holding the throttle at 25-35%? rather than smashing the pedal over and over?
• results of smoke test. I'm still betting on a gigantinormic vacuum leak.

please do check back.

Smoke test complete and no vacuum leaks found, and thank you for your help, that goes to everyone on this thread...

Now, no vacuum leaks detected, the resistance on the MAF is correct via the Bentley Manual specs. TPS is good, now I have to focus on the ICV...

How do I go about testing the ICV?

I will be working on the vehicle again today...

Originally Posted by E34_Obsession

Smoke test complete and no vacuum leaks found, and thank you for your help, that goes to everyone on this thread...

Now, no vacuum leaks detected, the resistance on the MAF is correct via the Bentley Manual specs. TPS is good, now I have to focus on the ICV...

How do I go about testing the ICV?

I will be working on the vehicle again today...

ICV is under the intake manifold. This will probably be your only project today...

DIY ICV Cleaning via bimmerwerks

Best of luck

Right I know where it is, would a sudden jerk or bump destroy an ICV?

Originally Posted by E34_Obsession

Right I know where it is, would a sudden jerk or bump destroy an ICV?

if i smashed it "suddenly" with a sledgehammer? sure. bumps in the road? nope. They're strong (being BMW built) but the valve is very sensitive...

Ok I will take note of that and be cautious. Now If I unplug the valve and stopper up the hoses to and from it would still start and run?!?

I'm not entirely sure. My best guess would be that it would take note of Throttle position sensor and MAF to run.

the point of doing that would be to isolate the problem, yes? you could try it and let us know, i dont see how it could damange the car, maybe throw and store problematic codes but hey, we're on a new frontier, aren't we?

Haha I guess so. I will be working on the vehicle this evening and will report back on what I find.

if you try to run it with the ICV disconected and isolated, i will be very interested in results.

I will keep you posted in what happens... Thanks for replying to my thread for so long!

never a problem. I live for diagnosing and troubleshooting. It's what we're here for.

Originally Posted by Monsignor

ICV is under the intake manifold. This will probably be your only project today...

DIY ICV Cleaning via bimmerwerks

Best of luck

The icv is new according to the op and no bad icv can cause those problems as seen on his video. Possibly due to either icv hose being disconnected but even then, the engine would not die quickly just sound terrible

Originally Posted by Monsignor

never a problem. I live for diagnosing and troubleshooting. It's what we're here for.

it would be better and more useful if you could give the op a baseline by doing an icv unplug and an icv hose disconnect both plugged and unplugged, and posting your observations. Since your engine is working fine and is the same as his. I would help but mine is an m52

M52 is just as close to his as mine is, so how about you go tear into your running car? Mine is a VANOS and his isnt.

Also my car is not running now, thanks though. Its not registered or insured and I have not installed my battery.

OP's "new" ICV could without a doubt be faulty and please oh please tell me how an IDLE CONTROL VALVE wouldn't be suspect in a terrible idle? Also, hose is not disconnected a smoke test confirmed, please read entire thread before posting, simple TOU...

An ICV would cause this issue, as many on this thread have said. I got busy yesterday and couldn't work on the vehicle. I will get around to it today.

Now I will remove the ICV and clean it out, plus test resistance and test its function today and get back to you later today

Mamij, read the forum before you post, like all the others do.

So we delete my post but let that ^ stay? Super cool...

OP please update on ICV

This thread keeps needing mod attention.

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