water pump now bad idle?

[Declasm]

I just replaced the waterpump on my '89 325i and put everything else back together - I didn't change the timing belt at the same time as I've since seen people advise. Now there is a problem that the car seems to be idling lower 400-550rpm than it was before and will sometimes stall coming up to junctions.

I've just had another look under the bonnet with the engine running, when I give it a bit of throttle it seems to take a second to jump into life and makes a bit of a "whooshing" noise just as the revs start to pick up - I think the noise is coming from somewhere near the air-intake / alternator / thermostat housing - can't quite work it out. a bit more info - It was raining for half of the time that I had the bonnet off much not to my amusement but I didn't have any other time to do the work.

[uzdubmwe30]

split air intake boot or youve left a vacuum pipe off somehow.

[JayB]

Check the alternator belt tightness. It could be too tight. or could of got wet.

[Declasm]

Check the alternator belt tightness. It could be too tight. or could of got wet.

The belt seems about the right tightness - maybe 6-7mm of deflection

What effect would there be if the alternator got wet? (which it almost certainly did!)

[JayB]

The contacts andbearing in the alternator may have got wet so it could do with drying out or blowing out with An air line? Can you put a long screw driver or somthing on the alternator to lisen were the noise is coming from?

[Declasm]

It's been a few days and ~100 miles since it was done so I think it would have dried out by now ?? The way the idle is low almost feels abit like there's an extra drag on the engine so it could be that the belt is too tight / alternator bearing is broken?

[JayB]

Try slacken the belt it off a little and see how you get on.

[Declasm]

I'm trying to think a little bit sideways - do you think moisture in the dizzy / rotor arm might cause idling issues - as that was exposed to the elements momentarily too.

I'll have another look at the belts tho - thanks.

[JayB]

Yea could be a little moist inside the cap, have you had any problem with it starting up?

[Declasm]

starting up seems just as normal - no probs there

[JayB]

It looks like water may have got in somewere, check you idle control valve give it a good clean out if its dirty, air intake cleaner will do the job. Make sure all of the wiring conections are clean and dry. Let me know how you get on mate.

Other than that mayby adjust the throttle slightly.