MK4 GTi bouncy idle

[elcono]

Morning chaps

I feel i have hit a bit of a wall and need to put the feelers out on a issue i am currently having

Previously the car was randomly bouncing down to 500rpm in traffic which when pulling away caused the car to stall. Multiple stalls later (and backing up the motorway slip road) i decided to have a look when i got home

logging the MAF input on a 2nd gear WOT run it tops out at 135gs (later found out should have done third). Looking at the maf flow it looks okay to me

The TB was caked in carbon (184k's looks never cleaned) so i gave it a gentle clean with TB cleaner. Now looks good as new

However now my issue is reversed. Instead of the RPMs bouncing down to 500 they now climb up and bounce when they hit 1200. I am assuming this is due to a set idle parameter somewhere

I have run a VCDS TBA post clean which made the car idle rock solid at 800, and this issue only seems to happen after 5-10 minutes of driving. Im guessing i need to break out a multimeter somewhere to isolate the bouncy idle?

remaining codes are

00282 throttle position actuator (v60) implausible signal
16507 throttle position sensor (G69) signal to high intermittent

Any nudges in the right direction would be appreciated

[JustCruisn]

All my idle issues have been caused by vac problems. Look for leaks.

[elcono]

i have tested to 15PSI. The system does not appear to be leaking anywhere and holds pressure for a good couple of minutes

[blackers10]

mine is doing both at the moment too...
sometimes it will drop and catch itself back upto 900ish?
then another time it will suddenly hit 1500 but if i blip the throttle it will go back to normal.

is it possible this could be related to a leaking Diverter valve? its the only thing I can think of that would let air around the TB and possibly seat funny if its not quite right causing the weird issues??
also super intermittently it will have a single what feels like a misfire when pulling away top of 1st or in 2nd gear.

similar to yours?

[elcono]

That's how mine used to be before I cleaned the TB of build up and ran a throttle body alignment in vcds

If I put on the lights, aircon, heated screen and radio it prevents it reaching 1200 and sits at 1100. So for now its at least driveable

I have reset the codes and will check to see what's been logged when I get to work tommorow. Fuel is about 600kms a tank on 98 which sounds normal ish. If it was a maf fault I would of though it would be a bit more eratic

[blackers10]

yeah I'm still pulling around 600-650 a tank.

[elcono]

update bump!

logged some more data with vcds

all the voltages are spot on when using 098 in vcds no jumps and the voltage scales all the way to WOT

One thing i did note was coolant actual hitting 99degress so i may have a look at replacing the sensor

As the voltages all read okay to the TB im going to take the side off and have a look to see if its gunked up from prior cleans. Slowly getting there, its just getting a bit old now as people think im revving my engine in traffic!

[tmh983]

99deg on the coolant is ok, mine will get up that high if i let it sit idle for long enough, i think the fans don't kick in until about there.
I think the coolant sensors read low when they go bad, mine would read about 30deg at full operating temp before i changed it...

[tmh983]

what is your lambda correction doing? (group 7), mine sits around +-5% which is pretty normal i think. You should see it switching up then down in response the oxy sensor feedback.
The other thing to check is your idle regulation correction value (group 5). Again, if its more than +-5% then it indicates a problem somewhere.
What temp does your IAT show first thing in the morning when the engine is stone cold? does it show the same as the ambient temp? Mine usually shows maybe 10deg warmer than ambient, i've ordered a new sensor to see if it fixes that.

[elcono]

Will check those tomorrow. I removed the TB and opens up the side. There were loads of score marks and deposits along the contact lines. Used electrical contact cleaner and a bud and took it out for a spanking, issue didn't occur in 30 minutes. Previous was always present........as always time will tell with the 30k commute tomorrow

UPDATE
Still hasn't returned after the commute. Will take it as positive if it stays away for a week

Wonder how many TB's have been binned and just not had their contacts cleaned that were actually okay

[blackers10]

wow. glad to hear its hopefully all sorted !

[elcono]

Yeah still good. Might finally be time for some half decent mods!

[elcono]

it was going so well

Came back today, busted out the multimeter

Pin
1 4.89v
2 0.02
3 0 (no pinout)
4 4.89
5 4.94
6 10.66
7 0.02
8 0.01

Had a look at a few diagrams and cant see which is signal? There is plenty of info for DBW but not so much for DBC

it was all going so well!

[elcono]

May have found a possible culprit

Screw on this sensor has been tightened so hard that its removed all thread and is just now wobbly

I have applied some sealant to see if it takes at all

I'm guessing the only option is to re-thread/tap the hole and use a slightly larger screw?

Would this area post TB always be under Vacuum? i wondering if its pulling it flush when idle and the pressure changes when gunning it are pushing the plastic out a bit which is causing the weird idle issue