engine and drivetrain my idle is doing something even wierder now.

[Guest dutch]

i was driving my car on the back roads pretty fast for about 45 minutes today and when i got home the car was idleing in the driveway and it was at 1000 rpms but it would go up and down and up and down. it would be at 1000 for a few seconds then go down to like 600 then back up then back down. this makes it really hard not to stall when accelerating. what is going on. my heat gauge doesnt say that the engine is heated too much so i dont really know what the problem is.

can anyone help me?

I DONT KNOW WHERE OR WHAT THE VACUUM IS AND HOW IT WOULD LEAK. SOMEONE HELP ME AND TELL ME WHERE IT IS ON A TII.

[PSloan]

check the fuel pump and filter maybe?

[Paul7002]

(nt)

[_z_]

The idle hunting problem has been said to come from running too lean -- This is all related to your cold starting problem and such. Your mixtures are messed up. Check these messages - and get that PDF and go through the KF system and make sure its in spec & the timing is set right

http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,26539/highlight,tii+idle+hunting/

http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,26802/highlight,ignition+hunt/

[polloelastico]

Check for play in your dizzy, could be shot, throwing your timing way off

[Guest dutch]

could this have any effect on my idle, and what is this. and im not very experienced terminology wise when it comes to certain things on cars, so i know i sound stupid but where is the vacuum on a tii

[BillWilliams]

one of two things, lean condition or vacumn leak.

If you have not tested your CO with a meter try richening up the mixture.

I assume you have done all of the tests for vacumn leaks

[ColinK]

Check for a vacum leak, esp. with the intake plenums. If you have a '72 with the plastic ones, check to make sure the rubber o-rings are not cracked, pinched, etc. If in doubt, order a new set from the stealer or one or your favorite internet sources.

Other things to check:

As C.D. would say: "check your points, dwell, and timing"

Change your gas filter (use the correct metal cannister one) while you're at it and clean in the in-line filters by the pump and at KF.

Clean the fuel pick-up screen in the gas tank too.

tii's use a mechanical advance for the distributor.

The oil should not be making a difference in your idle.

My money is on a vacum leak at the plenums.

the picture has me stumped. a wide angle shot may help.

[Andy74tii]

That, to me, looks like your decel valve, which is only on the '74 tii. I have a 74tii and I had the same symptoms a few years back. The decel valve basically quit, so I essentially bypassed it. I had to get my distributor recurved, however. I would try bypassing it first, to see if that does anything. The problem with a tii is that idle hunting is not uncommon, but it could be caused by many many things. The most common cause, however, is with the vacuum, usually a leak somewhere.

First pic below is "after" removing decel valve, plugging the hole in the intake, and routing intake vacuum line directly to the retard unit on the distributor. Second pic is original setup.

[jgerry2002]

Were your advance springs weak?

Why would you have to get the distributor recurved when the valve just affects the deceleration part of the advance curve? Isn't the idea of the decel valve is to slow down the dizzy from coming down from full advance for emissions sake?

Or is my thinking backwards on this?

My car ran MUCH better when I dumped the decel valve and went direct from the manifold. My dizzy is nice and tight with about 33,000 since a rebuild (around '89) which I'd guess included new advance springs.

[Zenon]

Andy74tii, I can imagine why recurving the dizzy might be deemed necessary, but given some recent personal experience I think you might have done OK by just disconnecting the retard module.

BTW, that valve on the air cleaner of '74 tiis is a "vacuum limiter", intended to reduce vacuum on overrun (which also reduces your effective engine braking) so that less oil gets sucked into the combustion chambers (thus lowering HCs). It should *not* be allowing air through at idle vacuum levels and so should not be affecting the vacuum retard action at idle. Vacuum retard is a method of reducing overrun NOx and HC emissions.

I just tuned a '74 tii that (among other problems) had a leaking vacuum limiter causing an un-tuneable high idle so I "converted it to '73 specs" by removing it entirely and plugging the port on the manifold. With it gone the y-connector was no longer needed so I then connected the dizzy vacuum retard module back to the manifold port.

That let me get a proper idle RPM and CO setting but on the test drive I could hear the engine was pinging, especially just off-idle (actually it may have been like this all along, I didn't test-drive it beforehand). Thinking more about the "'73 specs" that did not include a vacuum retard on the dizzy, I then disconnected the vacuum retard and plugged that port on the manifold, now relying only on the dizzy's centrifugal advance (just like '72 and '73 tiis). When I retarded the base timing to compensate for the now-absent vacuum retard action at idle, I found that the off-idle pinging was almost all gone and the engine was far more responsive overall. Some test drving and more tweaking resulted in a further reduction in the base timing advance and even better running. This was with 91 octane, the best universally-available fuel around here. If anyone cares, I can explain why this worked out, but I can already sense people's eyes glazing over...

To the original poster: Surging idle on a tii is a pretty sure sign of over-lean mixture (that could indeed be caused by a vacuum leak but maybe also because the idle settings have already been fooked with) but setting it right is not usually just a matter of turning one screw in or out until it gets better. There are a number of very critical inter-related adjustments - for example you have to be sure the accelerator pedal-to-injection pump linkage is in correct adjustment and in correct relation to the cam that opens the throttle butterfly. Fuel and ignition strongly interact on a tii so factory settings must be used as a starting point (despite what I said above) and only altered from that very carefully with some way of verifying that you actually are improving things.

It is admirable to want to learn to do your own work on your own car - and it is your right to do it as you please - but you need to recognize your lack of knowledge and skills before you ruin the car. Sure, I've learned a lot by breaking things, too, but I don't recommend that method for something as special as a tii. You really must get the factory tii tuning manual and make sure you actually understand what is going on with the adjustments, before you make things much worse. Maybe, for now, find an expert and just look over their shoulder. A tii is absolutely not the best car to be learning on - it is very easy to screw up the tune, the idle CO adjustment is super touchy and you need a CO meter, and almost any ham-fistedness will lead to damage. At least, learn enough to be able to ask a coherent question. If you have to ask "what does a vacuum look like?" or "what is CO?" you are not ready to be messing with any engine - let alone on a tii - no matter how much advice you might solicit on the web. Google, take a night school course, or read some auto-shop textbooks to learn the fundamentals of automotove engine theory and terminology - it will pay for itself many times over. Learn to fish.

regards,

Zenon

[Guest Anonymous]

This is a longshot, but check your motor mounts. When mine were bad, the engine would bounce around, changing the position of the throttle linkage and causing all kinds of mayhem.

It's worth looking into, at least.

[Guest dutch]

ya my engine shakes around a bit i may need new mounts but the pattern of the idle doesnt reflect the pattern of the shaking around, so im ruling that out

[Andy74tii]

Very good and detailed information here, greatly appreciated, Zenon. My mechanic (btw, he is also Bob Murphy's mechanic) suggested two alternatives - 1. keep the vac retard distributor or 2. get a fully mechanical distributor (ala 72/73). He said that my dizzy would probably benefit from a good overhaul anyway. So we went that route, and pretty happy with results. I have wondered about going to a fully mechanical 72/73 distributor, though. It is great to hear that you have good results with fully bypassing the vacuum. Again, thanks for the information!

[Zenon]

I have wondered about going to a fully mechanical 72/73 distributor, though. It is great to hear that you have good results with fully bypassing the vacuum. Again, thanks for the information!

From what I can tell of the specs published in the factory manual, the centrifugal advance curves of '72/'73 centrifugal-advance-only dizzies and '74 centrifugal-advance+vacuum-retard dizzys are very similar (both about 28 degrees of centrifugal advance range, all-in by around 3500 rpm). Of course, a worn dizzy sucks so rebuilding and recurving was a good plan. You can always try disconnecting your dizzie's vac module - you will have to re set the timing to get the idle back down and depending on if you were getting any pre-ignition before you may indeed notice a power increase. It is easy enough to experiement and set it back if you don't like it. The end result of a zippy-er car is ultimately what matters.

regards,

Zenon