Violently Rough Idle: HELP

[e30jake]

This is one of my first posts on m42club. I have been an active member on r3vlimited though for a few months now. I had a shell that needed an engine and a parts car with a good engine. I finished getting the replacement engine in and hooking up all the wiring (correctly as far as I can tell.) It is kinda hard to tell in the video, but there is just vibration everywhere. It starts and idles at around 750 rpm, but is unbelievably rough. The whole car shakes. Has only died once or twice, and it was while I was messing with stuff on the engine. If I unplug the AFM, idle goes to around 3000ish rpm. If I unplug the TPS, idle goes up a tiny bit then goes back to what it has been doing. If i unplug the ICV, idle goes to around 1500-2000 rpm.

When I first start it up the check engine light is not on. If I let it idle for a bit without touching the gas it comes on (like at the end of the video). As soon as I poke the throttle though it goes back off again. It also comes on if I hold the throttle steady (at 2000 rpm FWIW) and goes off once I let off. Tried stomp test for like 10 minutes and couldn't get it to throw any codes.

I tried a different AFM from an e36, a different TPS and throttle body from the old engine, different ICV from the old engine, and different ECU. Started and tested between each change. None of them changed anything. I searched and found that mystery plug by the firewall can cause idle problems if it is plugged in, so I unplugged it. Didn't help. I'm at a loss. I spent 4 hours today trying to figure it out and I'm no closer than when I started. It does seem to rev fine under throttle. Any other suggestions?

Link to video:
http://www.youtube.com/watch?v=vLClbPmjHn8

[Geoff]

seems like it might be a bad vacuum leak somewhere, rather than a bad componant.  Check all  vacuum hoses,  intake bellows,  etc
                                                       Geoff

[DesktopDave]

That idle seems to be at the right speed...mine runs about right there too.  I'd strongly suspect the DME is OK.

The new motor was running well before the swap?  Wasn't sitting for a long time?  If it's been sitting for a while I'd check the injectors, fuel pump and pressure regulator.

Does this happen all the time? Or only when the car is cold?

I might double check a few things:
Coils in the right order?
Coolant temp plug hooked up to the correct sensor?
O2 sensor OK?

I'd also be tempted to pull the plugs and check them.  You should be able to see if one is running rich, or has oil, etc.  Might point you in the right direction.

[e30jake]

seems like it might be a bad vacuum leak somewhere, rather than a bad componant.  Check all  vacuum hoses,  intake bellows,  etc

All rubber is in good shape. Did the mess under the intake while the engine was out of the car and used almost all brand new hoses.

That idle seems to be at the right speed...mine runs about right there too.  I'd strongly suspect the DME is OK.

The new motor was running well before the swap?  Wasn't sitting for a long time?  If it's been sitting for a while I'd check the injectors, fuel pump and pressure regulator.

Does this happen all the time? Or only when the car is cold?

I might double check a few things:
Coils in the right order?
Coolant temp plug hooked up to the correct sensor?
O2 sensor OK?

I'd also be tempted to pull the plugs and check them.  You should be able to see if one is running rich, or has oil, etc.  Might point you in the right direction.

The motor came from a car that was being daily driven until one day it wouldn't start. I went to see it, saw the intake boot was torn almost completely off the AFM and just figured that was the reason. The battery was dead so I never got to test the theory, since I was using the car for parts anyway.

The motor sat for ~6 months, and the fuel pump and FPR from the shell it went into have been sitting since early March. I am planning on switching to another set of injectors I have from an old m42 to see if that helps. The shell was being daily driven with no problems until a timing sprocket sheared off and the chain went everywhere.

It runs like this cold or warm. The coils are labelled 1234 by the PO of the shell, who was an enthusiast. I will double check the coolant temp and oil temp plugs and make sure I didn't mix them up later today. AFAIK, the O2 sensor is fine. If nothing else fixes it I'll try that. I'll also pull the spark plugs later today.

[DesktopDave]

I found this thread for the pinout...IIRC the middle pin of each coil pack is the trigger.  Please disconnect the DME before continuity tests...
Coil 1 - pin 25
Coil 2 - pin 52
Coil 3 - pin 24
Coil 4 - pin 51

I'd also check the CPS & clean it off nicely.  It should also be close to the trigger wheel, about a credit card thickness' worth.  The rusty debris that sticks to that sender tends to muck with a nice clean signal to the DME.  They're a well known issue with our cars.  Pins 1 & 2 should be 680 ohms +/- 10%...1/3 & 2/3 should be at least 100K ohms.

[e30jake]

I found this thread for the pinout...IIRC the middle pin of each coil pack is the trigger.  Please disconnect the DME before continuity tests...
Coil 1 - pin 25
Coil 2 - pin 52
Coil 3 - pin 24
Coil 4 - pin 51

I'd also check the CPS & clean it off nicely.  It should also be close to the trigger wheel, about a credit card thickness' worth.  The rusty debris that sticks to that sender tends to muck with a nice clean signal to the DME.  They're a well known issue with our cars.  Pins 1 & 2 should be 680 ohms +/- 10%...1/3 & 2/3 should be at least 100K ohms.

So i tried switching the temp plugs today. Car would start and die immediately so I'm pretty sure I had it right the first time. Also did a compression test and got 200-205 across the board. Pulled all the spark plugs and they all looked normal. There was a change when I switched the temp plugs back to normal. Instead of staying steady at 750 rpm it would die down to 400 or 500 then try to correct itself back up to normal then die back down again so I'm thinking I bumped a wire or something. Also, I'm assuming by CPS you are referring to cam position sensor not crank? I pull off the valve cover to see it and check the distance?

Bringing out the ohmmeter tomorrow. Pinout link will be helpful. I tried downloading the e36 Bentley from the references section and the link seems to be dead. Does anyone have another link that works? Either that or a link to somewhere that tells me how many ohms each sensor should read (I'll start with the ones already listed but I would like to be prepared)

[colin86325]

Sounds like one of the cyclinders might be dead.  Have you tried disconnecting the spark leads one at a time to see if this makes a difference? The one that makes no difference is the problem cylinder.