Funny Idle on 1.8t after Batt disconnected

[PhilR]

Hi

Mot is booked for sat and i wanted to fit new rear pads in advance of this. I disconnected the battery as i seem to remember reading that you you should when messing about with the braking system.

Did some other bits and bobs like clean up discs, oil and filter change then reconnected the battery and started the car. Note i din not change plugs I had the battery off about 2 hours

I turned the car a few times but didnt let it start to try and get the new oil moving round, then fired it up no problems. Turned off checked oil topped it up then took it out for a spin.

Warmed the car up driving sensibly then went to give it some stick. It seemed like there was no boost past 3k revs so went home and checked over engine bay connectors maf etc. Went out again same problem so i decided to take it down the a19 and it cleared up and felt as fast it should.

All i have now is a bit of an idle problem the car was really smooth before when returning to idle, now it seems to dip a little low then catch itself and level off at usual idle rpm. It only does this once which was an improvemnt from when i first started it

Sorry for the novel but i wanted to set the scene of what i have done and what the problem is. Anyone had any experience of this ? My mate has vagcom so i can get him to check for faults but it seems to me to be directly related to having the battery off.

Cheers for reading
Phil

 

[Siena]

Phil, you'll need to do a throttle body reset, disconnecting the battery makes the throttle body go out of sync, and lose it's basic settings.

You can use VAG-COM, or do a manual reset.

Manual procedure's as follows:

Disconnect battery, then reconnect after 5 minutes.
Switch on ignition, but don't start the car, or touch the gas pedal.
Leave it on for about a minute, switch off, then start as normal.

Hopefully, it works for you.

I also reset mine as follows:

I start my engine as usual, and it oscillates between 500 and 2,500 rpm
I dip my clutch, then engage second gear.

Handbrake on firmly, I release the clutch to the point it just bites, and drops the engine speed to 800 - 1,000 rpm.

I hold it there for about 1 minute, then keeping the clutch where it is, switch the car off.

Then restart as normal, always works for me.

If you choose this method, be careful you don't overdo it, and burn your clutch out.

 

[PhilR]

cheers for the rapid response Siena

Ill try this out tomorrow if it fails do you know how to do the vagcom reset on mine its a 98 1.8t Sport

 

[Siena]

I haven't used VAG-COM for the reset, but I've used the Snap-On scanner, I just went into Engine, then basic settings.

I didn't have to input any values either, it'll be the same with VAG-COM too.

 

[aragorn]

i THINK the TB adapts itself if you switch the ignition on and dont start it...

I know i can certainly hear a high pitched buzzing noise coming from the TB on both craigs S4 and our AEB engined 1.8T when you first flick the ignition on, which sounds exactly the same as the noise it makes when in adaption mode.

 

[PhilR]

Thanks for the advice took the batt off tonight and left it for 5 then ignition on till i heard the throttle body stop moving itself about started it and took it for a spin it all seems to be sorted now.

Just got MOT tomorrow to look forward to now fingers crossed

 

[andybnwc]

Will this work on a 95 1.8 N/A seems to developed the same thing after the battery went dead over christmas?

 

[Siena]

^^^ Yes, it'll work.