Idle repair opinions

[Kiwisholland]

I copied this from the Big Coupe Groupe Archive:

Idle Improvement - Engine Tuning - Don Eilenberger <[email protected]>

1. Throw out the Bosch Platinum plugs - they're basically not compatible with this car. Spend about $4/each for the Silver ones that are ESPECIALLY made for just this engine (check a BOSCH cross-reference book - guess what? The only engine using these plugs is the big 6!).

2. Set them to 0.032" minimum gap. Even to 0.035-38" won't hurt, the ignition system can easily handle it.

3. Install and TORQUE them in with no anti-seeze. 20 fl/lbs is about right.

4. Adjust valves to minimum of +0.002 over spec. +0.004 isn't even noisy and will help even more.

5. Run mega-dose of techron full strength stuff (not the watered down k-mart stuff) [mega-dose = 2 16oz can's in the last 1/4 tank. Run until almost empty. Fill up. Change oil!!).

6. Run the heck out of it. It will like it.

Problems with the '86-88 big six engine idle is related to exceeding (vastly) the EPA emissions standards. The things run VERY lean at idle (CO is almost unmeasureable at the tailpipe). None of them idle great - but the above can make it tolerable - and not embarrassing at a stop light (car rocking and rolling). The biggest change is made by opening up the valve adjustment, followed by the correct plugs and a wide gap. You'll notice as these open up with normal wear, the car runs better and better - I'm often disappointed after I tune BOHICA up, 'cause it runs WORSE - and end up resetting the new plugs to the gap the ones that came out were at - and doing the valves again. I'm currently running the valves at 0.014 +.001 - .000 - this seems to work well, and with BOHICA gonna reach 100,000 miles TOMORROW - the cam and lifters look JUST LIKE NEW - the car uses no oil, and the compression is excellent, and very even. It won't hurt the engine to run these wider - and will greatly improve the idle.

What do I set the valve clearance (lash) to on my '87 535i? The answer is 'usually 0.02" over specs' - which are 0.012" cold. So the answer is 0.014" clearance.

The reason - it helps the crappy idle these engines are afflicted with due to BMW's attempts to meet emission regs from around 1985-88 (they actually FAR exceeded them.. there is NO measureable CO at my tailpipe - have to go back to the exhaust manifold to see a reading).

If the car IS tuned to specs - it idles very poorly and tends to intermittently stall. Not all of this may be due to the valve clearance and plug gap - but using the wider settings sure helps.

Don Eilenberger says: What do I set the plug gap to on my '87 535i? I also set the plug gaps oversize - same reason again - in this case, spec is 0.028" - I typically use 0.032" If the car IS tuned to specs - it idles very poorly and tends to intermittently stall. Not all of this may be due to the valve clearance and plug gap - but using the wider settings sure helps.


Does anyone here follow this? I find it interesting. Slightly off topic, I noticed a huge increase in valve noise AFTER doing a valve adjustment a month or two ago. Engine now sounds like a sewing machine. Most of the clearances were very tight, I tried to meet the spec for a cold engine. Replaced banjo bolts with new ones with blue thread locker.

All the things I’ve done since I got the car in July with 121,000 miles have improved idle, but it’s still not smooth:
Plugs
Rotor
distributor
Ignition wires
O2 sensor
Coil
Cleaned ICV
Checked vacuum hoses and duct work

I’d like to try the bold quoted stuff above if recommended.

The fuel injectors were “cleaned and rebuilt” 5,000 miles ago, but that was YEARS ago. Fuel filter at same time. Might dive into fuel delivery system next. Then maybe AFM...

Thanks for your input

[plip1953]

Have you checked cylinder compression and/or performed a leak down test?