Rough idle and exhaust

Okay, what do i need to check when my idle isn't smooth? It's a 1995 540i. Also are there any pre fitted exhaust kits for it? Thanks for the help.

Changed plugs roughly 7,000 miles ago with iridium NGK's

everything, thats a very general question for a bmw


cheapest first, carb cleaner on maf iac tps
check plugs and wires for propper gaps and such
vacuum leak test for bad gaskets

Had a smoke test done and there is no vacuum leak. If that helps

You don't check anything. You replace the plugs, oil, oil filter, air filter, and at the shop replace gas filters.

And a premade exhaust kit is available from Billy Boat. Bought one from LMPerformance a few months ago.

Originally Posted by ThoreauHD

You don't check anything. You replace the plugs, oil, oil filter, air filter, and at the shop replace gas filters.

And a premade exhaust kit is available from Billy Boat. Bought one from LMPerformance a few months ago.

You can pull the plugs and check them, check the oil, air filter and check when fuel filters were done.

This is 540I.. spark plugs cost $$, two fuel filters $$ etc... it's not really 'cheap' to just throw parts at it IMHO. Oil is $70 for 8qts or whatever.

I would make sure the smoke test was properly done and pressurized first, check voltage to core sensors:

http://www.e34addicts.com/Checking_E...cal_Components

Do fuel pressure test:

http://www.e34addicts.com/Checking_Fuel_Pressure

Check your MAF and do compression test after.

If you are near NYC I can help you out.

Thanks for the help guys. My fuel filters were changed roughly 1500 miles ago and tune up was approximately 6500 miles ago. If the fuel pressure is low, which it might be, what do i check after the filters?

next in line would be ohm the fuel pump to see if its busted or weak

Would that be manifested in fuel pressure?

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ya, if the pump is weak then fuel pressure would drop accordingly, its just easier to test the pump than replace it,

Originally Posted by PFCTTZ

next in line would be ohm the fuel pump to see if its busted or weak

Ohm the fuel pump? You mean pressure test it with a gauge in driver side rail :P

no use a ohm meter to test the electrical connection of the actual fuel pump, but hey, what ever works

Alright I'll have it checked and see what happens. And if this makes any difference it idles funny only sometimes... It's weird

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Air leak..

Yeah i suspected that too but I had a smoke test done, and nothing appeared.

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1. Did you pull the codes from your car?
2. Buggy o2 sensor? When did you last change your sensor?

Three months ago I swapped the sensors.