Pulsing/surging idle - 2003 e85, m54, n/a z4, 2.5 l;

[asuleske@gmail.com]

THIS 2.5 ONLY HAS 22500 AND HAS BEEN SITTING IN THE GARAGE DUE TO WEATHER AND HEALTH RAESONS. SHE WILL NOT START EASILY. WHEN SHE DOES ALL I GET IS SPEED OF 1500 SURGING TO 2500 AND THIS REPEATS ITSELF ABOUT 6 TIMES UNTIL THE ENGINE DIES. RESTARTING THE ENGINE(IT DOES START IMMEDIATELY) ONLY MAKES THIS CYCLE REPEAT.
Q: WHAT DO I LOOK AT FIRST? I'VE SEEN THIS CLUE POSTED SOMEWHERE BEFORE BUT CAN'T FIND IT AGAIN. YES, I'VE CHECKED FOR VACUUM LEAKS. I CLEANED AN ALREADY CLEAN MAF. THE DISA IS NEW. I HAVE NOT CLEANED THE THROTTLE BODY - IO USED TO GET A CODE THAT STATED THAT THE TB DID NOT PASS ITS SPRING TEST. SO I'M THINKING THIS MAY BE THE ANSWER BUT BEFORE I START DIVING INTO THE WRONG AREA I'M ASKING THE PUBLIC FOR THEIR TWO CENTS OPINIONS. THANKS.

[Muzz258]

HI,

HAVE YOU EVER NOTICED THAT TYPING IN "ALL CAPITALS" IS LIKE SHOUTING AT SOMEONE??

I'll lower my voice now.

So, at the moment you have no trouble codes.

A couple of common causes for surging idle are:

1) A dirty Idle control valve. On the M54 engines, the Idle Control Valve is used to control the rev's up to about 2,000 rpm. Then the Throttle Body kicks in full time. Take the ICV out, spray it with brake cleaner to clean it and make sure it rattles when you shake it. Then give it a spray with a light oil to lub it. Something like CRC5:56. WD40 is not a lubricant, so don't use that.

2) Vacuum Leaks. Yes you've looked but there may be hidden leaks. Best way to find them is to smoke test the engine.

Alternatively, since you have a scanner, do this test.
With a hot engine at idle, check the 4 fuel trims, 2 short term and 2 long term. If any are >8% you likely have a vacuum leak. Rev the engine to 3,000 rpm for 30 seconds and watch the short term fuel trims. If they reduce significantly, might even go negative, than its confirmed that you have a vacuum leak.

[asuleske@gmail.com]

HI,

HAVE YOU EVER NOTICED THAT TYPING IN "ALL CAPITALS" IS LIKE SHOUTING AT SOMEONE??

I'll lower my voice now.

So, at the moment you have no trouble codes.

A couple of common causes for surging idle are:

1) A dirty Idle control valve. On the M54 engines, the Idle Control Valve is used to control the rev's up to about 2,000 rpm. Then the Throttle Body kicks in full time. Take the ICV out, spray it with brake cleaner to clean it and make sure it rattles when you shake it. Then give it a spray with a light oil to lub it. Something like CRC5:56. WD40 is not a lubricant, so don't use that.

2) Vacuum Leaks. Yes you've looked but there may be hidden leaks. Best way to find them is to smoke test the engine.

Alternatively, since you have a scanner, do this test.
With a hot engine at idle, check the 4 fuel trims, 2 short term and 2 long term. If any are >8% you likely have a vacuum leak. Rev the engine to 3,000 rpm for 30 seconds and watch the short term fuel trims. If they reduce significantly, might even go negative, than its confirmed that you have a vacuum leak.

I'll be diving into this assuming I have overlooked a vacuum leak or two. Too bad the ICV is not readily accessible but I'll bet I find a dirty one. With only 22k miles I don't expect to find things 'dirty' , however, sticky or tacky YES. Now also that I know how the 'spring test' works for the TCV while I'm down there I'll clean it also. Once I saw that code pop up but not again.
This design seems to be ??? a little complicated and sensitive to having a reliably performing engine - my opinion at this point. Since the car is 17 YO I suppose one must expect heat cycled rubber and plastics will need replacing. Thanks.