Flat spot when setting off

Mon Jan 16, 2006 4:58 pm

Im getting a big flat spot when i set of from standing and every time i go back on the throttle.
It ticks over fine, and goes ok the rest of the time, it does it hot or cold, i've changed the plugs/leads/dizzy cap/rotor arm, and cant see any air leaks.

Anyone got any ideas?

Cheers Sid

Mon Jan 16, 2006 6:20 pm

TPS possibly, i should click just as you open the butterfly on the TB.

Mon Jan 16, 2006 8:10 pm

Just tried that can't hear a click, is it suposed to click at the first bit of throttle?

Mon Jan 16, 2006 8:44 pm

Yes, i think it is meant to click as soon as you open the throttle.

Mon Jan 16, 2006 10:08 pm

skidlidsid wrote:Just tried that can't hear a click, is it suposed to click at the first bit of throttle?

Hmm they are a bit of a pain to adjust in situe as the adjusting bolts on the bottom of the TPS are hampered by the inlet manifold. Just take the throttle body off and do it that way, but use a new gasket.

You could cheat and lower the idle by twisting out the screw that controls where the butterfly closes to, perhaps try that and see if it gets rid of the hesitation, you want to be hearing that click with the slightest movement of the butterfly.

Tue Jan 17, 2006 1:30 pm

Got it adjusted now it clicks when you press throttle, but still same flat spot.

Tue Jan 17, 2006 2:05 pm

Wouldn't be the idle air control valve would it?

Mabey if it's a bit gummed up it might not be reacting as quickly as it should?

Tue Jan 17, 2006 2:24 pm

Turbo-Brown wrote:Wouldn't be the idle air control valve would it?

Mabey if it's a bit gummed up it might not be reacting as quickly as it should?

Yes that would be my next port of call, then try looking for air leaks with carb cleaner or the like.

Tue Jan 17, 2006 2:45 pm

Turbo-Brown wrote:Wouldn't be the idle air control valve would it?

Mabey if it's a bit gummed up it might not be reacting as quickly as it should?

Where is that situated at cant seem to find it in the manual
Is another name for it "idle air stabiliser valve"?

Tue Jan 17, 2006 3:27 pm

Yes thats the one. On this pic, hope you don't mind glen, its near the top of the picture directly above the dip stick tube. It'll have a plug on the end so check that isn't fouled up. It has 2 pipes going on the throttle body.

Tue Jan 17, 2006 6:10 pm

Right i'll have a go at that in the morning

Whats the best way carb cleaner or petrol?

Tue Jan 17, 2006 7:22 pm

skidlidsid wrote:Right i'll have a go at that in the morning

Whats the best way carb cleaner or petrol?

I think carb cleaner is usually recommended. I would be interested to find out how you get on as i have exactly the same problem with my '88 325i touring. Cheers.

Tue Jan 17, 2006 10:16 pm

Wid77 wrote:
skidlidsid wrote:Right i'll have a go at that in the morning

Whats the best way carb cleaner or petrol?
I think carb cleaner is usually recommended. I would be interested to find out how you get on as i have exactly the same problem with my '88 325i touring. Cheers.

I will post up my findings when i've got it back together.

Tue Jan 17, 2006 10:24 pm

Jon_Bmw wrote: You could cheat and lower the idle by twisting out the screw that controls where the butterfly closes to, perhaps try that and see if it gets rid of the hesitation, you want to be hearing that click with the slightest movement of the butterfly.

DON'T TOUCH THIS SCREW!

Wed Jan 18, 2006 1:21 pm

Got the idle air control valve of this morning, and noticed the big rubber intake hose that it goes into has got a small split underneath where it fits onto the airflow meter.

So i'll get one on order, i think i'm getting there now.

Sat Jan 21, 2006 4:39 pm

Update

In the end i fitted a new hose from the airflow meter to the throttle body, new hose from the idle control valve to the throttle body, and cleaned the idle control valve.

All sorted now flat spot gone tickover even better now.

Anyone else has similar problems check them 2 hoses they are only Ãƒ”šÃ‚£16.81 for the pair(well worth it).

Sat Jan 21, 2006 5:19 pm

Brianmoooore wrote:
Jon_Bmw wrote: You could cheat and lower the idle by twisting out the screw that controls where the butterfly closes to, perhaps try that and see if it gets rid of the hesitation, you want to be hearing that click with the slightest movement of the butterfly.
DON'T TOUCH THIS SCREW!

What are the exact implications of "touching" this screw? I could learn something here i think.

Sat Jan 21, 2006 6:50 pm

Jon_Bmw wrote:
Brianmoooore wrote:
Jon_Bmw wrote: You could cheat and lower the idle by twisting out the screw that controls where the butterfly closes to, perhaps try that and see if it gets rid of the hesitation, you want to be hearing that click with the slightest movement of the butterfly.
DON'T TOUCH THIS SCREW!
What are the exact implications of "touching" this screw? I could learn something here i think.

It's only got one correct position, and BMW set it there.
Moving it messes up the TPS and idle control function, so introducing more faults to mask the true faults.