[Mk2] [Turbo] Revs dropping to 300 rpm at idle

[joemacmr2]

More problems. Last week I fitted ebay intercooler, new clutch and berk decat.
Just last night, I noticed at idle the revs drop to around 300 rpm and car stalls unless u give it some gas. This is intermittent at the moment and only happened this morning at start up, then ran fine. Intercooler seems to be ok. Turbo is hitting full boost in every gear. All pipes are good and tight with no obvious leaks.
Can't see it being a problem with idle control valve or throttle position sensor as I never touched them whilst doing any of the work.

No fault codes shown in ecu

There is a red wire that runs beside intercooler that comes from cockpit into engine bay then goes into boot. Does anyone know what this is? It got tangled with fan belt and insulation was torn slightly until I realised and cable tied it out of the way.

[jasongtr]

vacuum leak?

[joemacmr2]

I did have my intercooler piping the wrong way around the other day so I took it out and fixed it up. This was the only thing I changed over the last few days so could it be a boost leak?

I always thought if I had a boost leak it wouldn't hit my target boost but it goes to 1 bar no problem.

[joemacmr2]

Was just thinking, whilst I was carrying out work I had to remove vacuum line that runs from oem bov to intake. When I was finished I couldn't find the hose and used a bit of different less flexible hose which didn't fit well at either end of bov/intake. Even had to slice it at intake end just to get it to fit over pipe.Could this be the culprit?

[bobhatton]

Was just thinking, whilst I was carrying out work I had to remove vacuum line that runs from oem bov to intake. When I was finished I couldn't find the hose and used a bit of different less flexible hose which didn't fit well at either end of bov/intake. Even had to slice it at intake end just to get it to fit over pipe.Could this be the culprit?

Yes

[joemacmr2]

Update: couldn't find any vacuum leaks. Vacuum hose from bov to intake was fine but I replaced hose anyway and clamped it tight. I topped up coolant the other day and think I put too much into the filler neck. I removed pressure cap today and a bit of coolant came straight out from cap as here must have been too much. I tightened it back up and from then the idle has fixed itself. No more erratic idle. Surely this couldn't be linked??? Weird!!

[joemacmr2]

Low idle back again when I went to work this morning. Sits at about 500rpm and engine starts to shake but it won't stall. Moved throttle position sensor about yesterday at idle and idle speed didn't change at all.

The only ignition component I haven't changed are the plugs which are original. Could it be these? Only thing is, car runs fine when given some throttle so unlikely

I did a part coolant flush the other day also (radiator and engine block). Surely this has nothing to do with it.

Any help appreciated as it's really starting to annoy me at this stage.

[jasongtr]

from what ive been told with my idle issue it could be the coolant sensor, so maybe as part of the flushing it has done something? just a thought

[joemacmr2]

Funny u mention that. My temp gauge usually sits around 8 o'clock (quarter up) at operating temp. Then when I drive around town, it will sometimes go closer to half and then all of a sudden drop below a quarter without turning off engine.

Maybe il try that. Do u know if temp sensor is the same on NA and turbo engine?

Did the sensor fix your problem?

[jasongtr]

not changed mine yet, waiting to hear back from ryan at 2bar tuning who mapped my car as some people have suggested it might of been mapped to idle that high so i might be looking for a problem that doesnt exist.

all ive done for the moment is disconnect my ISCV valve which drops my idle alot then used the manual idle screw to raise it back up a bit

very temporary solution for me but im not driving the car at the moment anyway, need to sort a better charge cooler out as my st205 one isnt up to the job i think

[joemacmr2]

If it was temperature sensor, surely u would get a ecu code??

[jasongtr]

Mine has a link ECU,

[joemacmr2]

Was thinking, when I did my part coolant flush, I Was having problems screwing engine coolant drain plug back in. It's as tight as I can get it now but it is by no means right the way in but I haven't lost any coolant. I have read that a guy had air in his coolant system which gave the same symtoms as me and a complete flush sorted it out. Maybe air is getting into the engine block due to drain plug not all the way in and upsetting the temp sensor signal to ecu.

Last night I released the pressure cap and coolant came flooding out. Then the idle was 100% the rest of the evening.

[joemacmr2]

Still trying to get to bottom of this. Pulled connector off idle control valve and revs stabilised. Is it supposed to do this or is it a sign that control valve is bad?

[Driftlimits Performance]

Randomly moving things and guessing is not going to get you anywhere.

The TPS must be calibrated to within 0.2mm otherwise the iscv will not operate correctly. They are also renowned for sticking.

However, its also a possiblity you've done something wrong.

You can't overfill the coolant from the pressure cap either.

[joemacmr2]

Really don't know where to start now. So many things could have caused this. I'm just not convinced it's anything to do with tps or idle control valve.

[joemacmr2]

Going to go back to the drawing board and start with intercooler pipe work and work from there as I was messing about with fitment the day before this happened. Although it does make peak boost, I have read that there can still be a boost leak only turbo has to spin faster.

Would a slight vacuum leak in pipe work cause the low idle? What's the easiest way to check hoses with air compressor? Spray carb clean around joints?

Low idle is intermittent. Low when I reversed out if drive way. Fine during my 1.5 mile commute to work and then when I pulled up t work car park, engine died.

[joemacmr2]

Have finally linked my problem to a fault within the ecu. Has anyone ever experienced this?
In the meantime I was going to run with the Idle control valve unplugged. Is this ok to do?

[jasongtr]

one of my old rev3 turbos had the iscv removed and a blanking plate over it, when cold it will be a little low but ok when its warmed up

[joemacmr2]

Did unplugging it have any ill effects with running or was it just the idling?