Hot Ambient/Load Idleing issue (A3 1.8T)

[Tallpaul]

Righto...

Posted about this a while back. But still got problems so looking for new ideas.

Problem:

In warm weather (ie ambient temp >23°C) i get an issue where if i rev the engine or drive along, then disengage the clutch and allow the revs to settle to idle they don't; Initially the revs stick around 1500rpm the slowly fall to about 1000rpm then dip/climb between idle speed and 1000rpm in an erratic fashion. This is even worse when the Air Con is on.

Ok, so there is some sort of problem with load correction and throttle control.

To rectify this i've tried:

Resetting the ECU
Cleaning the TB and doing a TB Alignment
Replaced the Coolant Temp Sensor
Replaced the MAF
Replaced the DV
Replaced most of the hoses with silicone ones

The only other obvious thing to try is replacing the N75, how much do these cost?

Does anyone have any other ideas?

 

[jesters3]

Worth plugging it in to VAG.COM to see if any fault codes come up? Standard N75 valve on Vagparts is £33 https://sslrelay.com/s74326199.onea...nid=1545014e05cf021/shopdata/index.shopscript

 

[Tallpaul]

When i first bought the car there was a 'Throttle Position Actuator' Fault code. It was listed as intermittant. I stripped the throttle body and cleaned it then cleared the fault. It hasn't returned since and i've had no other fault codes.

Although that fault appears related, it's never returned. Apparantly the fault is related to the micro-switch(es) that are in the Actuator. There is no 'repair' so it'd mean a whole new throttle body.

What makes me think it isn't this is that surely the fault would be unrelated to air-temp or engine load as a faulty switch would randomly mis-behave, not predictably?

The N75 that VAG-Parts list is for the S3 and newer A3's. I need one for an AGU engine code.

 

[madvw]

other than the stuff above, the only thing i can think of would be throttle postition potentiometer and/or lambda probes.

Microswitches usually just stop working rather than play up.

 

[Tallpaul]

other than the stuff above, the only thing i can think of would be throttle postition potentiometer and/or lambda probes.

Microswitches usually just stop working rather than play up.

I'm fairly confident (famous last words) the fault isn't in the throttle body.

My car has a throttle cable (AGU engine code), so no potentiometer to worry about.

Also, i think i only have the one Lambda probe on the downpipe. So that's one less to worry about. If it is the Lambda probe it'll eventually go completely and it'll be pretty obvious it's ******. If it is that, i'm more than happy to wait for it to fail completely I think i've found a dirt cheap Milltek 2.5" downpipe and race-cat; i'll have the Lambda probe inspected while that's fitted.

 

[madvw]

aah, have you tried replacing the throttle cable? they can get water in and get sticky and or rust.....

if it's intermittantly sticking, that may throw the microswitch error...

 

[Tallpaul]

aah, have you tried replacing the throttle cable? they can get water in and get sticky and or rust.....

if it's intermittantly sticking, that may throw the microswitch error...

I haven't replaced the throttle cable but i also don't think it is this. There is no feeling of sticking through the peddle and i haven't had a single instance of engine speed not immediatly decreasing when the throttle is released.

When this fault occurs, although the engine speed does 'stick' around 1500rpm it was also rise and fall around the idle speed. A stuck cable would not cause the revs to increase?

Although the throttle is cable actuated. Idle speed is still controlled by electronic adjustment of the throttle butterfly valve. VAG-COM shows you that the throttle only needs to be open around 2° to maintain the idle. In fact something like a valve open >2.3° at idle indicates a leak in the boost/vacuum hoses between the throttle and turbo outlet.

Something somewhere is basically telling the ECU to open the throttle too much or it's getting conflicting signals or it is simply unable to compensate for extra load... I've no idea what all the inputs for these calculations are and i've replaced all the obvious ones (bar the N75).

 

[dubhyper]

easy ...paul the hunting of idle speed you mention. I have started to have the same problem. the only performance mod i have is a cold air induction. the problem has only begun to occur since fitting...... maybe just maybe it could be something to do with that.and the ignition thingy (gotta love my terminology) with the heatsink backing that was on the orignal airbox . what do you think...just throwing an idea?!?!

 

[Tallpaul]

hmmmm, well my ignition thingy is still in the OE airbox... It could be be stuffed though, maybe it's overheating and therefore is worse when it's hot/under load?

I'll whip it off and see if the heatsink and conducting goo are OK then clean up the contacts. They ain't cheap to replace!

 

[Tallpaul]

Well i've now ditched the OE airbox and am running a Carbonio CAI. I've relocated the ignition thingy (complete with its heatsink) and after extensive testing I can't say it actually gets that hot?

The car was doing the crappy idle thing this morning with the AC off and ambient temp of 12°C. It's really starting to **** me off now

If i had a spare £500 i'd change the coilpacks, sparkpugs, Ignition thingy, throttle body and N75. But i don't, so instead i'm gonna carry on whining about it on the internet.

 

[Prawn]

easy ...paul the hunting of idle speed you mention. I have started to have the same problem. the only performance mod i have is a cold air induction. the problem has only begun to occur since fitting...... maybe just maybe it could be something to do with that.and the ignition thingy (gotta love my terminology) with the heatsink backing that was on the orignal airbox . what do you think...just throwing an idea?!?!

sorry to bring up an old thread, but was this problem ever sorted?

my car now does this, and i never noticed it before i fitted my cold air induction system. its now noticable in all weathers, although it doesnt always happen, it seems pretty random at the moment.

how have you guys relocated your heatsinks for the ignition thingy? i simply pulled mine across the the nearside as much as possible, and zip tied it to the cold air induction pipe with the heatsink touching it, the pipe stays pretty cold during use, and the ignition thing (sorry i dont know what it actually is) hasnt ever gotten very hot at all....

could it be something to do with the cold air kits using oiled filters and effecting the MAF?

 

[Tallpaul]

nope, mine still does it

lost interest in trying to cure it. I don't think i ever will.

 

[markyp2002]

i had this exact problem ive changed ****** everything

MAF
DV
N75
Air Filter (still wearing OE airbox).

Only started happening when ambient outside temperature started getting colder (during winter).

Ive got a feeling its something to do with the CAI in the passenger side wing and the OE air box. Everything after there i have replaced and still have the problem.

Ive also recently changed all the coil packs, spark plugs, leads to no avail!

 

[Tallpaul]

It's most likely a very small leak in the vacuum system. But there is a lot of hoses to change, i've done about half. I may do the rest when the weather gets warmer.

 

[markyp2002]

woiiii ive found the problem .....

i nice big crack in the pipe leading from the turbo to the intercooler, id imagine the quick drop in temperatures outside as caused it.

so if your having the intermittent problems of lack of boost/no boost, idling funny (skipping between 800-1100) have this pipe checked.

If anyone knows what this pipe is known as or a part number it would be a lot of help

 

[Tallpaul]

Like i said, i believe it is a hose somewhere along the way. All number of hoses are under vacuum at idle and a split in any of them *could* cause this problem.

The intercooler hose you mention has already been changed for a Forge Silicone jobby in mine...

 

[markyp2002]

where did you get it from and how much did it cost you if you dont mind me asking?

 

[Tallpaul]

I got it from Forge...

Came as part of a 5 piece set of replacement boost hoses, cost around £120 for the lot.

 

[markyp2002]

Never mind ill change this lol, im taking you bought these ones?

http://www.forgemotorsport.co.uk/images/products/FMKT005.jpg

 

[Tallpaul]

Never mind ill change this lol, im taking you bought these ones?

http://www.forgemotorsport.co.uk/images/products/FMKT005.jpg

Yes.

Which of these was split on yours?

 

[markyp2002]

the big fat red one

the one with the bend in it.

caused me a lot of ****, ive changed the MAF 4 times now thinking it was that =x