Rough idle & more

[Alpinerob]

Ive been working on a 1992 318ic for almost a year now.. havent had to do much to the engine but its been sitting since I got it.

recently the car stopped firing up...always did immediatly...but i replaced the the fuel pump and now its alive again.. however... the idle sucks...when it first kicks over, the idle is either holding at about 2500 or its up and down all on its own.. after a minute or two it will go back to normal idle, but it will be rough..then die..

all of the vaccum hoses are solid & connected.

I will say that while testing the car before I changed out the fuel pump, i had to jump it at one point from trying to start all those times.. I crossed the neg & poss. on the car like an idiot and fried the cables..

with that said, is the rough and unstable idle due to a bad ECU..? or would it not even start if that were the case??

pulling my hair out at this point..

[kwill22]

Um, yea. If you crossed the cables there's a ton of electrical things that could go wrong. Have you fine through all of your fuses and relays to make sure they're still good? I've seen even new cars Christmas tree'd from from someone hooking the cables wrong.

[Alpinerob]

all of the fuses appear to be fine, just as before.. I keep thinking ECU, which is not a huge problem, but wouldnt fuses protect it from a surge like crossing the cables?

I dont have the tools to test the relays just yet, but perhaps the main dme relay is cooked.. but if that were so, would the car even start?

[kwill22]

If the main relay was bad it wouldn't start. Do you here it clicking when you turn the key to the on position?

Fuses protect the systems they're connected to from spikes/surges but crossing the cables is another issue. I'd say it's 50/50 something gets fried. But since your car starts and at least runs albeit crappy is take that as somwhat of a positive. Did you try the stomp test?

[Alpinerob]

stomping the gas..?

i have another ECU & alternator on the way.. the battery needs to be charged as well before I move on to more diagnostics. Hoping the ECU is fried.

[roguetoaster]

The stomp test, where you key the car to on, but don't start, then pump the throttle pedal to the stop 5 times.

As far as crossing the + & - terminals I've done it a couple of times (insert excuses here), so far it's not damaged either of the 318s I did that to. Not saying it won't but as soon as I saw sparks I removed the lead.

[bmwman91]

Maybe try cleaning out the idle control valve? My car sat for about 9 months and the ICV was all gummed up when I went to start it and it was idling at 1000-2500RPM. Shoot some throttle body cleaner or rubbing alcohol through it. Before that, you can try starting the car and tapping on it with a screwdriver to see if that helps by knocking the little vane loose.