M42 won't hold idle UPDATE: New problem. Need help

[shameson]

*See update at bottom of post*

Ok so not long ago my car died while driving thanks to a failed alternator. Had it towed home and got to work.

Replaced:
• Alternator
• Alternator and PS belt
• Intake boot (mine was old)

Fired it up and it wouldn't hold idle. Would start up, then start sputter out at 1500 rpms. Car would stay running as long as you kept revving it. So back to work. It's a 23 yr old car with parts of unknown mileage, so I decided to just do it all knowing my problem could be numerous things.

So over the last month I've replaced:
• Most of the hoses and vacuum lines. Tackled the mess under the intake
• Throttle position sensor
• Cam and crank position sensors
• Fuel and Main relays
• Fuel pressure regulator
• New spark plugs
• New ignition coils
• Valve cover gasket (pulled the valve cover to paint it)
• AFM works just fine. Put it on a buddies car and it ran smooth as silk. Even tested his AFM with no change happening
• Tried a spare ecu, no change

So still SOL, have had it idle for 30 sec- 1 min twice but that's it. Only things left I can think of is ICV and fuel pump. But at ~$175 a piece for a new one I want to get advice.

Anyone have ideas of what I'm not considering? Or whether it's the ICV or fuel pump?

11/15 Update

So after playing around with the car, I've made some progress. I guess.

Replaced the fuel filter and put a spare fuel pump in I got from a friend. At this point, checked the cps resistance and it's in spec. This is where I'm at at now:

So after sitting, the car will cold start fine (probably due to extra fuel injected). It idles nicely, very smooth and doesn't shut off randomly. Once it warms up, if your shut it off and restart it, it will continuously crank roughly and will barely start. Seems to only want to fire if you give it a little throttle.

But now driving, in the low end it's fine but between 3.5-5k rpms the motor practically cuts outs and as if it's totally out of wack. At this point idk where to go. I wanna lean towards timing being the issue but this is getting over my realm of knowledge

[Kurt V]

First lesson: quit throwing parts at a car until you know what the problem is! Cause now you don't know if any of the new parts might be bad or you installed them incorrectly.

Lecture over. Now some questions: Did the engine run ok prior to the alternator problem? Next: are you sure you didn't kill your battery? Check it. If less than 12.3 volts with a multimeter, you may have a bad battery.

[shameson]

First lesson: quit throwing parts at a car until you know what the problem is! Cause now you don't know if any of the new parts might be bad or you installed them incorrectly.

Lecture over. Now some questions: Did the engine run ok prior to the alternator problem? Next: are you sure you didn't kill your battery? Check it. If less than 12.3 volts with a multimeter, you may have a bad battery.

I didn't put in all the parts at one time, I've been doing all this over the course of the last month trying to do it in steps: tried just the AFM first, then tried just the cam, crank sensor and tps, then just the fuel relay next, etc. That's just a list of what I've done so far. Sort of throwing parts at you could say, but methodically to see if anything changes it. It's all stuff I'm glad to know is new lol

And yes battery was replaced at the beginning of this year. I have a multimeter and the battery was between 13-14 volts when I started the car after replacing the alternator, when the problem first occurred

[roguetoaster]

When I arrive at a mystery such as you have I try to eliminate parts from the equation. In your case I suggest removing the ICV from the system and setting idle at the throttle body. That should tell you what you need to know.

[shameson]

When I arrive at a mystery such as you have I try to eliminate parts from the equation. In your case I suggest removing the ICV from the system and setting idle at the throttle body. That should tell you what you need to know.

Thought you're not supposed to mess with the idle screw?

I'm going to try cleaning my ICV and see if it makes any difference

[roguetoaster]

Technically it's a throttle stop on the TB as it does nothing more than adjust how far open the butterfly valve opens. You may be thinking of the idle adjustment screw on M20 ICVs (I forget if the M42 has one).

My thinking is that if the engine can hold an idle that way you should be good to go. A first step if you don't want to try that might be to just unplug the ICV.

[shameson]

Technically it's a throttle stop on the TB as it does nothing more than adjust how far open the butterfly valve opens. You may be thinking of the idle adjustment screw on M20 ICVs (I forget if the M42 has one).

My thinking is that if the engine can hold an idle that way you should be good to go. A first step if you don't want to try that might be to just unplug the ICV.

If I just unplug the ICV, how should I tell whether it's the issue or not?

[roguetoaster]

If I just unplug the ICV, how should I tell whether it's the issue or not?

Unplug, adjust the throttle stop until you are 900+/-50 RPM. See if the idle stays steady.

[FCBmw]

I seem to be having a similar issue. My car seemed to be running ok with the revs up but every so often it would really run like crap. Especially when starting up in the morning. The car would barely idle almost like running out of gas. When I could get it going with the revs up at normal driving speeds it would be ok. When I came to a stop it would stall out or stumble. After it would start up every time. I unplugged the ICV and besides a high idle it has yet to have any of the mentioned issues. It also threw a code of c9 (lamda control). So I am just wondering if this tells me that the ICV is bad? Also is it ok to drive around with it unplugged?

TIA

[jdt10768]

clean shit from ICV with carb cleaner, reinstall. test.

[FCBmw]

Is it possible to pull it with the manifold on?

[jdt10768]

You can just unplug and remove. It's between the valve cover and firewall. Held on by a 10 or 13 mm bolt I think, and a couple small hoses.

Elec plug has a small wire retaining clip that will fall into the engine or onto ground. Use needlenose

[roguetoaster]

You can just unplug and remove. It's between the valve cover and firewall. Held on by a 10 or 13 mm bolt I think, and a couple small hoses.

Elec plug has a small wire retaining clip that will fall into the engine or onto ground. Use needlenose

It's an 11mm nut that is the far right hand side of lower intake manifold.

The plug on most of the ICVs I have seen is the push down on the metal spring to release type, don't use pliers unless necessary.

If you have yet to do the mess under the intake work the ICV will be a bit fiddly to reinstall due to the shape of the lower hose going to it. This hose is also prone to cracking, be sure to look at it if the above applies.

[econti]

Can you hear any air leaks? Sounds like what mine was doing.
Do all the mess under the intake. Replace all the hoses and simplify the whole thing.

[shameson]

clean shit from ICV with carb cleaner, reinstall. test.

Ya I need to try that. Im going to soak in carb cleaner an see what happens

Can you hear any air leaks? Sounds like what mine was doing.
Do all the mess under the intake. Replace all the hoses and simplify the whole thing.

Ya I've already looked at the hoses/ vacuum lines and replaced just about all of them. Had a few that were bad but replacing them didn't change anything

Eventually I'll go through and simplify the whole deal