efi High Idle At Normal Operating Temperature

[ck_74tii]

Newbiw here. I have recently purchased a 1974tii. It seems to have a high idle speed at normal operating temperature. The rubber connector from air filter to throttle housign has a hole in it but idle did not change when I covered it with my finger. Any suggestions?

Thanks in advance.

[eurotrash]

Oh man. <<Wince>>

[eurotrash]

Ok. 1. That car has no MAF, no ECU, and therefor vacuum leakage doesn't play on the running condition as it would a moder..er EFI system. Anything before the TB is just intake charge. Filtered or not filtered.

So forget everything you know.

Your Tii has several mechanical, electrical and moving parts that can effect running condition. Use the search feature and be sure to select "forums" as the search location. Use every key word you can dream up as it relates to a Tii injection system. Read all you can on the operating principles of the KF MFI system. The pump, the injectors, cold start valve, tuna can adjustment, and linkage settings. Once you have basic working knowledge of the systems, the trouble shouting (yes, shouting) will be less of a stab in the dark and will save you tons of time and pesos.

Edited January 24, 2014 by eurotrash

[eurotrash]

...and your questions will become less general, and less like raw meat for the lions.

[OriginalOwner]

euroT is spot on !!

 

Two air leak possibilities come to mind.  I'll think of more later.  And the worst part:  it may not even be an air leak problem.  I don't know much about the KF system in general, but it sure ain't no carburetor kinda thing in terms of troubleshooting similarities ... but sometimes it is ..... or not.  All part of the fun and terror of owning a '74tii.

 

FIRST.

There is a small rubber hose on the "back" side of the throttle housing ..... "back" meaning on the firewall side, as opposed to the "front" radiator side.  A very short small-diameter rubber hose which connects between the throttle housing and the larger-diameter rubber hose which connects left-right from the top rear end of the valve cover over to the air filter housing.   

-----  The small hose is quite well hidden underneath the big aluminum 180-deg curved air pipe whatever-its-called, see picture below.  The hose is under pipe #3.  You'll probably have to remove pipe #3 to get at it, not to worry.  Remove the air filter and all 4 nuts securing pipe #3 are quite easy to reach & remove, piece of cake.  If you do remove it, BE SURE to write "TOP" on the top of the pipe, I'm pretty sure top is top and bottom is bottom and cannot be interchanged.

 

And, there is a plastic thingie which sticks into the large rubber hose and has a "barb" projection on it, and the short small-diameter tube fits over the barb, and the other end of the small tube fits over a similar "barb" on the back side of the throttle body.

 

Finally after all that;  I've had problems with that plastic thingie leaking air, the hole in the larger rubber hose gets distended.  And the small rubber hose getting so old & crusty it no longer fits tightly over the barbs and leaks air.  Heck, that small hose could even be missing, and if so, I hope that plastic barb thingie for the larger hose isn't missing.  Not a show stopper, I'm sure Ben at 2002AD has one.  Or you can redneck engineer something.  Or maybe the experts around here will tell you that that hose is not critical and can be ignored all together .... there might be a thread somewhere that talks about it.

 

SECOND.

The small diameter rubber hoses (3 of 'em) that connect between the distributor, the plastic thingie Y connector, the air filter, and big 'ol aluminum air plenum thingie to which are attached the 4 180-deg tubes.  Any/all of those connections can be leaking air.  Here you can see the 3 small rubber hoses connecting onto the Y connector .....

----  ALSO note that one hose goes to that aluminum thingie on the black air filter, so logically that larger rubber hose on the other side of the aluminum thingie can be leaking too.

 

OH, and on the bottom of that aluminum thingie there is a very short rubber hose into the black air filter.  In 39 years I've never replaced it, but ......

 

 

Cheers,

 

Carl

Edited January 24, 2014 by OriginalOwner

[bnam]

if you have the valve on top of the air cleaner, try plugging the big hose -- I've experienced the valve sticking open -- when it's open it lets in air from the filter into the manifold.

[Chamoix]

When I see discussions like this it makes me really happy I DON'T have a tii !!

[ck_74tii]

Thanks for the informative reply. I will spend some time checking out your suggestions and report back. Cheers.

[willys]

what is your idle rpm?

[ck_74tii]

After careful monitoring og my idle here is what i found. the idle is not always high. It was ~900 rpm at te beginning of the drive, then it woudl stay at 1500 rpm when i hit a light, i blipped the throttel, the engine would rev and drop back down to 900 rpm sometime but more often than not it was at 1500 rpm.

OriginalOwner - I noticed that the hose form the rear of the throttel body was just dangleling freely not connected to anything yet.

Bnam - how do i know if the valve is open or closed- wjhat is th epurpose of that valvle attached to the air filter housing.

[bnam]

I checked mine by putting a plastic hose clamp on the bigger hose the goes from the front to the manifold.  The moment I clamped it, the idle changed -- indicating there was air going thru it.

 

So, I removed the hose and plugged on both sides.

 

However, there is a symptom on my car that seems similar to yours.  My car starts and idles just fine.  HOwever, when after it has warmed up and I come to a stop when I let go the throttle it will occasionally idle at ~1500.  I've noticed that if I put it in neutral and let go the clutch, or even in gear let go the clutch just enough to slow down the engine a tad, the idle will drop to 900 and stay there.  I've not been able to find the source of this air leak.  I do have a theory.  My theory is that the leak is from around the edge of the warm up regulator - that at higher manifold vacuum (throttle closed) there air getting by it, but when the engine slows down a tad, the piston in the regulator seals up again and cuts off additional air.

[Guest_anonymous]

What is the condition of your distributor. It doesn't sound as though the advance mechanism isn't returning to the idle state correctly. And/or your timing is to far advanced to compensate for another issue. Remove dizzy cap.and rotor oil the felt under the rotor in the hollow of the distributor shaft. Replace cap and rotor. Check dwell angle/points if applicable. Check timing. It may take some time for the oil to work into the shaft. If condition persists, try a different distributor to isolate the problem.

[ck_74tii]

Bnam - I plugged the larger hose the goes from the front to the manifold when the engine was at high idle and viola it returned back to normal. I (quickly) plugged it back to the valve, tapped on the gas and the engine went back to high rev. plug the larger hose and it went back down. I woudl like to replace that valve rather then completely bypass it. At this point I do not know its function and suspect bypassign it altogether might cause more isses. My 2002 manual is still not delivered. Any thoughts?

 

OriginalOwner - I noticed that the vaccum hose form the rear of the throttel body was just dangleling freely not connected to anything yet.The original larger-diameter rubber hose which connects left-right from the top rear end of the valve cover over to the air filter housing has a hoel to insert the above mentioned vaccum hose. Apparently I am running without this vacuum feedback. Do you think it is worth getting the original pipe (11151252665 fom AutohausAZ) where there exists a hole to attach the vaccum line form rear of throttle?

 

 

 

[OriginalOwner]

Can't hurt to put it to original condition, but I honestly do not know "why" that connection exists.  If it is simply blocked off, I don't know how it affects engine performance in terms of "balance."  It is there for a reason but I don't know the reason.

 

(more)

I just found this great picture of the hose (from jgerock) .... and he says, "The little vacuum hose should be tightly connected to the breather hose."

 

SO, YES, you want to have that hose connection between throttle body and bigger hose.

 

Reading on the topic:

http://www.bmw2002faq.com/topic/132953-tii-tuning-vacuum-leak/

http://www.bmw2002faq.com/topic/129979-tii-throttle-body-vacuum-line-came-off/  

 

 

Cheers,

 

Carl

Edited January 29, 2014 by OriginalOwner

[bnam]

That valve was introduced to help with emissions.  My understanding that it is similar in purpose to a dashpot on a carb -- slows down the rate at which the engine slows down when throttle is released to help with emissions.  While a dashpot physically slows down the throttle return, when the throttle is closed on the Tii, the high manifold vacuum causes the distributor to retard and this valve to open up allowing additional air into the manifold keeping the revs up.  The valve should then close slowly decreasing the bypassed air and lowering rpms.  Perhaps the valve is sticking open, in my car it was staying open longer than it should.

 

Valve is NLA.  I wonder if some lubricant will help with the sticking.  Disconnecting the valve and the retard on the distributor would mimic the set up on the pre-74 Tiis.

 

Byas