ANOTHER idle question (I know, been asked 100Â’s

[klu99apm]

The car is an 1988 325i touring (105k miles)

After installing an LPG kit to my car my idle is crap! When starting the car from cold it starts fine and idles at about 800-900 rpm for a few minutes. However once its been driven a bit and its warm when you come to a stop and take your foot off the gas the revs drop to 400 Ԛ—a 500rpm and the lights on the dash often come on Ԛ—a sometimes it stalls and other times it will manage to tickover badly for about 5-10 secs and then the revs increase to 600-700 and it idles perfectly and smoothly. The car drives perfectly the rest of the time.

It does exactly the same on gas and on petrol.

The idle of 600-700 seems a bit low as before the work it used to idle at 800Ôš'ish, but I guess IÔš've added a plate mixer and an anti-backfire catflap device so the airflow might be slightly impeded from what it was before at idle.

The problem seemed to start when I disconnected the battery for around 5hrs on Sunday and maybe the ECU isnÔš't learning the new idle?

So far IÔš've:

1) Checked for leaks using carb cleaner
2) Cleaned the ICV in carb cleaner
3) Checked the TPS (it clicks perfectly and the gas software tells me its sending out the right voltage)
4) IÔš've checked the resitance across the ICV pins (20ohm between 1 and 2 and 2 and 3)
5) The ICV receives 12.5V from the centre pin, 2.5 from the outer pin and 7 from the other outer pin with just the ignition on.
6) The car has been driven over 250 miles since the problem and idled for over 20mins so the ECU should have re-learnt the idle settings.
7) If I disconnect the ICV while idling the revs drop to 500 and stay there (although it ticks over nicely) as soon as its plugged back in the revs increase to 600Ôš'ish
8 The ICV buzzes when ignition on

All I can think of to check is:

1) The AFM (but this doesnÔš't do much at idle does it?)
2) The blue temp sender (but as the car will idle perfectly once it decides to go to 600 rpm I discounted this initially)

Any thoughts as this is really bugging me and doesnÔš't sound to me like other descriptions IÔš've read when I did searches. Sorry for re-asking a common question but I've searched through many old posts and can't find the answer!

[dasparkybad]

sounds like your throttle butterfly is not open enough on tickover to give you a good baseline idle you need to adjust the throttle stop screw slightly (turn clockwise) but make shure your tps still clicks off once you have adjusted it or your idle valve will not kick in at tickover

[klu99apm]

Thanks for the reply.

I've adjusted the screw perhaps 1/2 a turn and thats as far as it will go before the TPS clicks.

The idle is much better already (it doesn't stall anymore but the idle speed is only a bit faster and it still bogs down a bit before idleing smoothly.

This weekend I'll have to take the whole throttle butterfly assembly off I guess, and adjust the TPS so I can get a bit more adjustment - is this an easy job?

[stuartforrest]

I had this problem, it was running really rough and when it went to idle it cut out, it turned out I had two problems.

I suggest you:

Check all pipes connecting to the ICV, i thought mine were ok but it turned out there it was perishin on the underside.

Try and get a hold of another AFM and try that with it!

I tried adjusting the throttle as a quick fix and yes it did work but it's not ideal!

[Brianmoooore]

sounds like your throttle butterfly is not open enough on tickover to give you a good baseline idle you need to adjust the throttle stop screw slightly (turn clockwise) but make shure your tps still clicks off once you have adjusted it or your idle valve will not kick in at tickover

DO NOT TOUCH THIS SCREW, and if you already have, put it back wherte it was!

[Brianmoooore]

The extra resistance to airflow from the venturi mixer and the cat flap will be negligable at idle, compared to the AFM door and spring.
Have you sealed the joint between the AFM and catflap properly? Is the rubber band on the catflap seated properly? And check the big rubber air hose very carefully.
Slightly odd idle behaviour is fairly coomon on LPG, because the ICV becomes slightly worn in its normal operating position on petrol, and sticks a bit when asked to operate in a slightly different position on gas. This shouldn't affect things on petrol though.

[klu99apm]

aaaghhh

I'm getting conflicting advice now!

Last night I took the TB off and cleaned it up with carb spray. It seems that the previous owner had set it to be totally shut at idle, and it was quite dirty with carbon deposits etc. I read elsewhere on this site its supposed to be 0.75mm open at idle, so I set it up like this, adjusted the TPS, and fitted it this morning.

I've only warmed the car up on idle, not driven it yet, and only tried it on petrol, but it seems to be much better now, idling really smoothly at about 700 - 800rpm.

Everything is definitely sealed properly but I'll replace the big rubber air hose soon, as mine is looking a bit perished, even if its not leaking yet.

I'll leave it like this for a while unless what I've done is wrong (Brian?) as at least it seems good now.

Thanks for the replies!

[Brianmoooore]

DON'T TOUCH THIS SCREW only applies is its not been got at before of course. Should be only very slightly open as you say. It is NOT an idle adjustment.
Its a good idea, with a LPG powered car, to tighten the big jubilee clips for the big air hose only just tight enough to stop them pulling off.