Rough idle

[dvmotorsports]

So we picked up a 91 MT2 318is for my wife last night. 101,xxx 5spd ......................$900.

Anyhow, it's got a rough idle. Here is what I have done since I also have an M42.

Changed the plug wires, coil, and intake boot. Rough idle still present. So I disconnected the ICV (at least i think it was the ICV, on the intake opposite of the throttle cable. Minor change in idle and the CEL came on. So given that info, could that be it? I figured the CEL was from lack of signal. So I assume even though it maybe faulty, it's preventing a CEL. Is that possible?

Those things are a bitch to get out and I don't want to do it unless I have to.

[dvmotorsports]

Getting fault 1216, Throttle Potentiometer. Perhaps that is what I disconnected.

[fiftytakedowns]

hey,

The TPS and the idle control valve work off of eachother.
Id recommedn you take a multimeter to the Throttle position sensor, and see if it variates correctly with the position of the throttle. supposedly from 2-4 volts or something along those lines.
if the TPS is bad, I think the ICV wont work.

but vacuum leaks could also be the cause of a funky idle, which you probably already know.

and you did disconnect the throttle position sensor. The ICv is located near the firewall right next to cyl 4 intake runner tube. hope it's a help

[dvmotorsports]

I suck at electrical though. Yeah I have checked for vac leaks, nothing yet. There was a fuck load of the conductive grease in the plug wires and in the plug valleys. I though it was arcing, no dice. The tach is out but i hooked up my meter and got a reading of roughly 850 on all the cylinders.

And this car smells as if it's running way rich.

[dvmotorsports]

So cyl 1 appears to be dead. I have fuel, but no spark. What triggers the firing on this motor?

As for the rpm signal i had, must of had the pickup on the wrong wire. Went back and it was zero.

[dvmotorsports]

from what i see in the wiring diagram, the DME controls the spark. dunno if that is right though

[dvmotorsports]

Swapped DME. Fail. Still no spark on #1

[dvmotorsports]

Okay so since I suck at electrical, follow me on this.

I volt tested each connector from the DME to the coil at the coil. I also took Ohm readings on the coils. The ignition was obviously on. Here we go.

There are three pins on the connectors at the coil, one is + the other two are ground i'm guessing. Thus I received two reading on each connecor.
#1 8v and 12v
#2 12v and 12v
#3 12v and 12v
#4 12v and 12v

Coil ohms
#1 0.3
#2 0.8
#3 0.8
#4 0.7

So it appears there is a problem not only with the coil, but in the wiring as well. Like I said before though, I swapped with a known good coil and still had the same problem.

[fiftytakedowns]

you should check the ohms on your crank position sensor, and your cam sensor, cause those both control spark I believe.

hopefully all your engine grounds are good.