VR6 high idle when hot - occasional not all the time... grrrr.

[mookie 0]

I'm having an occasional and unpredictable issue with my VR6. Every so often, and literally it's only every few days, the idle will sit anywhere between 1000 and 1250rpm when idling if the car is hot. It never does it cold or luke warm, but only when the coolant gauge is showing around the 95-100 mark and the oil temp is up 100+. Even then, it's not everytime either. Most of the time it idles just fine, but then recently it can sometimes just suddenly not drop back to a normal idle speed.

 

When it sits high, the car will otherwise run and drive fine. I have been having a seperate annoying kangaroo, off-throttle jerk happening when travelling at very low speeds/revs, so I'm not sure if there is a connection there? Like I say it's not a daily issue, but I have noticed the pattern/connection between engine temp and the higher idle. One other weird thing, a week or so ago, when it was stone cold, I turned on the ignition and the car revved itself to about 1500rpm five or six times immediately after it started, before settling to a normal idle. It's never done that before or since :scratch:

 

I'll give you an example.

 

Today I left for work, and ended up (unusually) stuck in traffic. Temp gauge going up, MPG going down... :bonk: after a short burst between lights, when I came to a stop the idle stuck at 1250rpm-ish. I gave it a rev, no change it still wouldn't drop back. Tentative crawl forward in gear, all normal rev wise, popped it out of gear and it goes back to 1250rpm. Long blast along a dual carriageway (60ish), pulled up at more lights, now it's a shade over 1000rpm, coolant and everything is still about the same temp (fan running). Pulled up at work, still over 1000rpm although slowly, very slowly dropping. Reversed into my space, revs drop to a normal idle/reverse rpm with barely any throttle. Back up to 1100ish out of gear.

 

I took the ISV off at the weekend and cleaned it out with carb cleaner - in comparison with some totally filthy 16v ISVs, this one was really clean anyway. The throttle body is similarly very clean, with no visible crud or oily residue in the pipework. It's been put on VAGCOM a week or so ago, and the only codes it threw up were for a fault with a rear ABS sensor (obviously irrelevant to this...) and the speed sensor error that apparently should be ignored as the car was static (from a seperate search I did). I've tried unplugging the MAF and it cuts out so that seems to be doing it's job. I can't see any airleaks or split pipework and I've gone over every hose clip and checked they're nice and tight. Loom look intact, no frayed wires or dodgy repairs I can see, connectors look nice a clean (the ones I've pulled out). Car has been recently serviced (Jan/Feb) and was given the works by Stealth in April last year (£££££'s on the bill) so I'm hopeful it's not leads/plugs etc. Like I say, it drives lovely, pulls really hard and fast, sounds lovely, no hesitation under load etc... so I'm a little stumped as to why every so often it decides to idle differently?

 

 

Any help greatly appreciated! :cheers:

Edited June 13, 2012 by mookie

[KBN-STANCED 10]

Probably the temperature sensor on its way out mate :-D

[dr_mat 0]

I get this when the alternator isn't charging the battery. Basically any of quite a lot of different fault statuses on the ECU will cause it to go to a high idle.