M42 engine won't stay running after rebuild

[CFELD]

Aftering running at 1.5k to 2k rpm for about 5 minutes the engine will idle alright. Prior to that it runs like garbage. This car is a real mystery to me. I bought it for $800 on the side of the road and rebuilt the engine. I think I did everything with that fairly accurately. Now I have the car running and it won't idle. The spark plugs make it look as though it is running lean. What could be wrong?

[Froos]

The idle control valve might be out?

[CFELD]

I don't think it is but I just had to order a new hose to the icv cause mine was badly cracked.

[Darky]

Hi

This is strange, typically idle goes bad after the car goes into closed loop ie warm.
Not when it is cold open loop. In open loop the Ecu runs the engine by memory ignoring the o2 afm sensors. That's a dead give away for any cracked pipes ie car runs fine till it's warm.

Yours is backwards, crank and cam sensors are always used for ignition and fuel.

Stomp test?
Fuel pressure?
Did you disconnect ecu when you where rebuilding engine?

Cheers Rohan

[colin86325]

Yeah, kinda reminds me of the behavior when you disconnect your battery and the ECU has to relearn its parameters and causes the car to run like crap for several minutes.

[CFELD]

I did disconnect the ecu while I was working on the engine because I was testing some wiring. Stomp test gives me 1222. When sparks plugs are pulled they show that the mixture is rich. I do have fuel pressure. I did the timing myself without a tool (cause I'm on a little bit of a budget), but I would think that even if the timing is off a little bit the car would still idle.

[Darky]

1222 means too rich or lean

Causes afm, air leak, engine temp sensor, fuel pressure, spark plugs or valves.

Do you have a spare afm? Can you borrow one from someone?

Because nearly all the others are crossed off because it runs well in open loop.

Hope this helps

[CFELD]

No local spares. It could be the valves. the timing could be a degree or two off maybe. This car say for 10 years before I bought it so something may have gone wrong with the temp sensor. The spark plugs were new so it's probably not that. I could have a bubble in the system by the coolant temp sensor to ecu, but the coolant temp gauge seems to be working and the sensors are right next to each other. I still need to pick up my hose from the local bmw dealership cause the bottom one that was going to the icv valve was cracked badly. I know I have enough fuel pressure to get the car to idle cause I've jumped the fuel pump relay with the fuel line off and a lot of fuel poured out. I think it may be a combination of the valve and maybe afm. Is there a way to tell if the afm is bad?

[CFELD]

I just replaced the hose and it still would not idle. I just order a camshaft timing tool for $85. Will I have to remove the upper chain case cover or just the valve cover?

[Froos]

I would also check the fuel pressure at 46psi or 3 bar minimum

[CFELD]

What would I use to test the pressure. As well as doing this while I had someone in the car keeping the car running I unplugged each spark plug wire. The result was a slight drop in rpm but the car did not run any more rough. Crossing my fingers it is just the valve timing

[Darky]

You can test the afm using a multimeter on ohms.
While your there clean it using electrical parts cleaner.

[Froos]

What would I use to test the pressure.

Buy from ebay or amazon or lockal petboys a fuel pressure tester, cant be more that 40$..i believe the m42 is quite sensitive for the correct pressure, good practise to test on any 25 year old car

[CFELD]

It idles now. It won't die anymore. I have a really bad slapping and the car won't go into gear. Looks like it's time to part out.