engine and drivetrain wandering idle problem

[schnell944]

hey all,

been sorting out the new A4 2002tii lately. after replacing the alternator bushings and tightening the belt it certainly runs better and doesn't squeak anymore. thanks for those who helped with that!

the car also had problems at idle where the engine speed would slow to the point of stalling. this no longer happens. what is happening now is that the idle speed will tend to wander. it will hover around 1000rpm then drop a little, stay there for a bit, then maybe slowly climb up to 1500rpm....then go back down. it will do all of this in a random sequence. when driving the car it performs normally, however, except for the above promlem when idling.

also, if i rev up the engine just a little past 1000rpm it will tend to want to stay there and not want to drop back down normally.

I am wondering if anyone has an idea of what might be causing this. seems like something may be sticking? any suggestions on what to look at would be greatly appreciated! thanks

Ryan

[BillWilliams]

On the a4 there are four individual idle adjustment screws that control the air at idle.

There is also an intermediate shaft with a thumb wheel locked by two 8mm lock nuts. THis controls the fuel at idle.

Getting all of this in synch takes some time, dumb luck and an ounce or skill.

You can try to close down each idle by pass screw a bit to see if this richens things up a scooch. If that does not work, and you feel adventourous, the fuel adjustment is next.

Alpina info on the way.

[dapbmw]

vacuum leaks at intake manifold, throttle bodies, thrrotle shafts leak too and will be expensive to rebuild/rebush on the a4 tb's. throttle shafts might be binding too and maybe your return springs are weak so replace them. check your 4 idle enrichment screws and the balancing lever as you may be out of sync. been there done that!

[BillWilliams]

carb cleaner around the shafts, if the idle varies, you have leaks. SOme use a propane torch, NOT LIT, to find vacumn leaks too, less messy some say.

I searched for a year to have my manifold rebuilt. Finally, Mr. Bieker, of Bieker Engineering took it on and did a really nice job, He bored out the throttle bodies to make the 45mm on both sides of the butterflies. He recut and angle the butterflies plates, rebushed and o-ringed the shafts.

A web search may turn him up, if you are into a rebuild, I can look up his info for you

[schnell944]

thanks for some direction in my tinkering guys!

ryan

[c.d.iesel]

...............also another wild theory from

a very experienced BOSCH injection pump expert:

if the injection pump is bound up with too much oil - also

meaning oil is not free to return to the block - the pump internals

will not advance and retard fuel delivery properly.

A chassis dyno with exhaust gas tester is needed to adjust any injection

pump correctly. A portable gas tester or O2 sensor set-up is another

way to correct air/fuel ratio's

AND - revisit the ignition advance/retard control with a timing light

throttle flaps all closed ? and sycronized ?

[ingraham]

(nt)