what causes high idle?

MARCANNEKE · 05-13-2013, 07:39 AM

Hi there,

I have some problems in fine tuning my 2.0L 914-4. It's equipped with the original d-jetronic, and last winter I did a major service when the motor was out of te car.
Since then, on restarting, I suffer from high idle. I tried everything, checked all hoses and replaced them, all gaskets are replaced with new ones from Pelican, but I seem to search in the wrong direction. I tried an electronic replacement for the condenser, but it gave the same result.
Anyone with a tip for the next step? is it possible that I mis adjusted the valve clearance and is that the reason why the car skips into high idle?
Please help this pour fellow, as I have to do a road trip on 20/5, and with this high idle I don't know if the car is 100% trustable.
Greetings

Marc
Zele
Belgium

MARCANNEKE · 05-13-2013, 07:46 AM

I forgot to tell You guys that I already checked the AAR and the MPT. They are OK.
Throttle valve switch seems to be OK too.

John Rogers · 05-13-2013, 08:18 AM

I would suggest trying the "spray carb cleaner" method to see where the vacuum leak might be. Any place where air can sneak into the engine can be suspect such as: throttle body base to plenum gasket, intake runner tubes(rubber ones), intake flange to head joint gasket, fuel injector O-rings and even a crack in the intake plenum (we had one of these).

MARCANNEKE · 05-13-2013, 09:03 AM

John,

So valve clearences are of no influence? I just put up new gaskets on the covers, so if not needed I would like to leave them untouched.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Valve clearance is unlikely to cause a high idle problem.

You almost certainly still have a vacuum leak. Pull off the hose going from the oil filler to the manifold and plug the hole at the manifold. If the idle drops, then your PCV valve may be stuck open.

Overly-advanced timing can make for a high idle, too. Double-check the timing.

--DD

MARCANNEKE · 05-14-2013, 08:41 AM

OK, I'll try the carb cleaner method. I'll keep You informed.
Wish me good luck!
Marc

MARCANNEKE · 05-27-2013, 08:59 AM

Hi again,

Recently I found that when disconnecting the temperature sensor on the cyl.head ( commonly known as the TSII) the engine seized immediately. Can it be that the sensor gives faulty signals to the EFI, and that therefore the engine dares to backfire from too rich mixture? And also causes the high idle I struggle with?

Greetings,

Marc
Belgium

Dave at Pelican Parts · Dave at Pelican Parts's Garage

When you disconnect the head temp sensor, the FI thinks the engine is colder than the south pole and will command pretty much as much fuel as can be delivered into the engine. It is a very rare circumstance that allows the engine to run with that much fuel going into it...

BTW, "seized" implies that some parts of the engine welded themselves together and the engine will no longer rotate without "heroic" measures. If you cannot even turn the engine over at all with the starter, you have "hydro-locked" it. That's where there is so much liquid in the combustion chamber that there isn't even room for the piston, so when you try to make the piston rise it gets stopped by the non-compressible fluid. You can remove the spark plugs and see if the engine turns over at that point--keep your face away from the engine bay and keep an extinguisher on hand, because you can get nice little fountains of gasoline coming out if that is indeed what is going on. (Don't ask how I know that.)

--DD

MARCANNEKE · 05-28-2013, 07:16 AM

Dave,

I mis-used the word seized, as English is not my native language. I should be that the engine stopped turning from the moment i disconnected the TSII.
On reconnecting the wire, it run like before. There was never a problem with a blocked engine or so...

John Rogers · 05-28-2013, 08:18 AM

Did you ever try spraying carb cleaner around ALL the hose connections as mentioned earlier, including the inlet plenum since they can get cracks over time. Other places that can cause air leaks is the base of the throttle body and the joint where the intake runners fasten to the heads as those joints will get warped.

Racer Chris · Racer Chris's Garage

It is not unusual for the 2 liter intake plenum to develop cracks which create a significant vacuum leak.

MARCANNEKE · 06-03-2013, 07:52 AM

Update 2/6/2013,

I found the vacuum leak!! it is between the intake runner and the cylinderhead on the driver-side. I don't understand it because the gasket is a new one from Pelican Parts. When I spray carb clean over the joint the idle goes up for 2 seconds and then drops to the former RPM. I think I have to do this job over!!

Marc

John Rogers · 06-03-2013, 08:27 AM

I would suggest pulling the whole intake system off and redoing all the joints since if one is leaking the other might start also. Generally the head is fine but look closely at the sealing surface to make sure there are no cracks or dried sealant, etc. For the intake runner, obtain a straight edge and use that to check for the flatness of the sealing surface and I'll be it is warped or there are some left over gasket materials. While the intake plenum is off, look closely at the bottom to see if the rolled joint has bad looking places and I always used a light coat of Goop sealer all around just to be safe.