Engine sitting just below propet idle speed

[Cocopops101]

Hi everyone, new driver and learner fixer here looking to find out how to fix my old banger of a 2005 severely underpowered 1.6 s40 lol iv recently had to remove battery as i removed seats, airbag connectors ect to replace carpets. Since doing this my car has started to play up by sitting just below battery charging idle speed and have had issues with radio not wanting to turn on sometimes even though light comes on for few seconds and yesterday i had to get a jump start as wouldnt start on me. When mechanic jimp started car he said there was charge in the battery and engine was charging ok but i have noticed that when i start it idles higher for few minutes like normal then drops to half way between 500 and 750 revs and its causing my battery to drain. Is there any way to fix this as iv read few posts about retraining ecu or cleaning throttle body ect but they all are for different versions of volvo's so could anyone tell me what im supposed to look for and how to fix if possible please as its ****ing me off having to sit for 30 mins after every journey with foot on gas pedal making sure iv got a charge for next mornings nursery run. Any help would be gratefully recieved. Thnx in advance fellow volvo-ists :^)

[iain cooper]

have you checked that all vacuum pipes, etc have been reconnected ?

Iain

[Cocopops101]

lol no vacuum pumps were touched i only removed the battery for internal work removing seats, all air hoses ect remain as they where. i have no vacuum leak i had that checked before i posted.

[richard]

Car should still be charging when driving it.
You spend little time at idle.
Simple test, put headlights on, start the car, do the headlights get brighter?
If no difference, its not charging.

[Cocopops101]

@ richard thanx for reply.
I have tried headlights they do get brighter but not by much as they are standard crappy bulbs so not very bright to begin with lol i understand what you mean by car should charge when driving but its only short journeys I'm doing 4 or 5 times a day say around 1 and half mile to 3 miles at a time so not getting a long enough drive to proper charge it up and when sitting at lights, junctions ect idle speed is just below the charge mark of 750 revs and causing it to loose charge. I can tell its draining as radio has now started turning off to save power soon as i put it on or until i have done a longer run to give it a charge. I can tell this as when engine just switched on radio refuses to switch on but if i sit with revs up for 10 to 15 minutes the radio will then come on again. Im wanting to know how to clean the throttle body of this model if possible anyone can post how to do it as all other vids are for different version and looks totally different. Or whether its possible to turn the revs up myself somehow. Any ideas helpful so again thanx richard for replying atleast it gave me something else to try lol

[richard]

You should take the battery off overnight.
See if that helps.
Sounds like you battery has had it. once started it will run off the alternator.