Need help diagnosing fuel/ignition problem

[traqrat]

I've noticed if I don't drive my car for a week, it has trouble starting. In addition, the idle is a bit rough (when the engine is cold or warm). I took a look at the sparkplugs and 3 of them look healthy, while the other 3 are sooty. I'm thinking since only 3 of the cylinders are not burning cleanly, it probably isn't an ignition problem. Anyone have suggestions as to what I should check next? Does this sound like I've got clogged injectors?

Thanks in advance.

FYI: I've got a 1990 325i

[jbob]

have you kept up w/ regular maintence....how long ago did you replace the battery? fuel filter?

it may be a slight fuel problem, if those 3 sooty spark plugs are kinda white, then ur burning lean in those cylinders, maybe try running some fuel injector cleaner. if that doesn't fix it, check the fuel pressure on all the lines.

it could also be some bad spark plug wires, or even a vacuum leak

[traqrat]

Originally posted by jbob
have you kept up w/ regular maintence....how long ago did you replace the battery? fuel filter?

it may be a slight fuel problem, if those 3 sooty spark plugs are kinda white, then ur burning lean in those cylinders, maybe try running some fuel injector cleaner. if that doesn't fix it, check the fuel pressure on all the lines.

it could also be some bad spark plug wires, or even a vacuum leak

I'm not so sure about the maintenance history of the car. I just bought it a few months ago. The battery is only a few months old.

I'll try the injector cleaner first to see if it helps.

The other thing I noticed with the sparkplugs is that only half of each plug has any discoloration. The other half looks brand new. Is this a characteristic of single intake valve engines or does this indicate another problem?

[Bill]

If i remember correctly the e30's have a cold start valve located on the intake manifold.

[jbob]

doh, forgot to ask........does your car idle rough all the time???? does the tach seem to wonder randomly between 500and1000rpm??? and you need to open the throttle slightly so the car won't die? if so, then you just have a vacuum leak...

i'm not 100% sure, but i think the e30 m20's don't have a cold start valve since it's an efi setup.....i know i have one on my k-jet (non efi) m10.

[traqrat]

The RPMs don't fluctuate very much. It's just when it's idling, I can feel and hear a very slight sputtering for a second, and it pretty much alternates between this and smooth every second or so.

[jbob]

you could try this, it's right out of the haynes repair manuel....

if the sparkplug looked kinda grey all over then it's too hot....recommendations: check for the correct plug heat range, over advanced ignition timing, lean fuel mixture, intake manifold vacuum leaks, sticking valves and insufficient engine cooling.

if the sparkplug is covered w/ carbon deposits...(caused by a rich mixture and/or weak ignition)...recommendations: make sure the plug has the correct heat range, check for a clogged air filter or problem in the fuel system or engine management system; also check for ignition system problems.

i think you have the carbon deposits one....so lets see what else can you check.....if you have a rich mixture, make sure the fuel pressure reg isn't clogged up (one guy on the roadfly forum had a similar problem w/ sputtering and the fpr was at fault)....

but i'm leaning more towards an ignition problem since you noted only 3 of the spark plugs had soot on it (a fpr fault would make all the plugs look sooty). take a look at the distributor cap and rotor, the contacts for those 3 corresponding plugs might be worn....or you might have bad spark plug wires.

[traqrat]

Ok, I just checked the ignition wires and it turns out the 3 wires going to the sooty plugs are about 400 ohms higher than the other 3. According to the Bentley manual, this is within spec., but I'll try putting in new wires and see if that solves the idle problem.

[Andrew9682]

You might also want to check out this like from the old BEN site.
http://www.e30forum.net/technical/45.html

[UD///M]

Originally posted by Bill
If i remember correctly the e30's have a cold start valve located on the intake manifold.

Only the earlier models have a cold start injector. His, being a 1990 model would not. One possibility is that you have leaky injectors. Another possibility is a leaky intake manifold gasket. Try spraying some carburator cleaner at the junction of the head and intake manifold while the engine is running. If the engine stumbles then you have a leak.