hunting idle when cold - Page 8

BIGGYIN · 18-02-11, 07:22 PM

Well,that probally won't help.

Gouldy · 18-02-11, 07:23 PM

will have a look in a min!! got to go out to the garage anyway, will check the readings hot and cold!

Gouldy · 18-02-11, 08:00 PM

i bloody give up!! volt meters broke now!!

i unplugged both of the sensors on the stat housing and they made no difference

however when i unplugged the ISV and plugged it back in a few times, it seemed to run a bit smoother , cant tell bugger all now the volt meter is broke

Obli · 20-02-11, 11:28 AM

Quote:

Originally Posted by Gouldy

When i unplugged the ISV and plugged it back in a few times, it seemed to run a bit smoother , cant tell bugger all now the volt meter is broke

I also have a hunting idle on my 20v when the engine is cold. The revs also have a habit of dropping down to 500rpm when I slow down and come to a standstill and change down to first gear. I started my car from cold and after 20 seconds, removed the power connector to the ISV. My car immediately stalled. I wasn't expecting that. What should it do if the ISV is OK / not OK?

Gouldy · 26-02-11, 03:16 PM

just done some checks on the sensors

the Thermo time switch when cold has a resistance of 32.3 Ohms
the warm up reg when cold has got 21.3

the top sensor on the thermostat housing has 0 when cold and 35 when warming up (i think this sensor is just for the temp gauge???)

and the bottom sensor on the stat housing is 0 ohms when cold and 0.1 when hot, however if unplugged the idle rises quite considerably, so it must be doing something?

any ideas guys

Phil Payne · 26-02-11, 04:00 PM

Quote:

Originally Posted by Obli

The revs also have a habit of dropping down to 500rpm when I slow down and come to a standstill ...

Working as designed. Idle is kept high to provide power steering assist until you're moving slowly enough not to be making steering inputs. The drop point is usually between 4mph and 6mph.

Obli · 26-02-11, 04:23 PM

Quote:

Originally Posted by Phil Payne

Working as designed. Idle is kept high to provide power steering assist until you're moving slowly enough not to be making steering inputs. The drop point is usually between 4mph and 6mph.

I am fairly sure it didn't do that before. When it started doing it two or three years ago, I removed the ISV and cleaned it. After refitting the ISV, it seemed to be cured of this issue it for a while... now it's back! If I am moving in slow moving traffic, as I am slowing to stop, clutching in as I pull up (and at about the speeds you mentioned, perhaps lower), it drops temporarily (I forgot to mention that before) to the 500rpm range then fluctuates a couple of times between 500 and 1000rpm, eventually stablising at 900rpm when at a standstill.

fj1200 · 26-02-11, 08:25 PM

Greetings guys.

New to the forums, let's see if I can help here.

First and foremost, we need to decide if the idle hunting is a function of the ISV circuit or fuel mixture. A lean fuel mixture will cause surge in RPM, the ISV may not be able compensate fast enough to cancel out the surge. You stated that the engine appears to be running rich when hot. If the control pressure regulator is not operating properly someone may have adjusted the baseline fuel mixture to run properly when hot, but still be able to start. We know the thermo time switch wiring was damaged and not allowing proper function of the cold start injector.

I would start by repairing all wiring at the thermo time switch and then testing the circuit. Use a 12V LED with a 1K ohm resister in series with the positive leg of the LED. unplug the blue connector at the cold start injector and connect the LED to the harness. Crank the engine and make sure the LED lights up. if no light, test for 12V to pin 2 of the connector while cranking. If no power, then inspect all wiring at the starter closely. If no groung (earth?) then the thermo time switch may be faulty. After this circuit is sorted we move on to mixture control.

The best first step is to find someone with a set of CIS fuel pressure gauges, control pressure cold should be around 25 psi and hot around 52 psi. Convert to metric as needed. If control pressures are not is spec. disconnect the 2 fuel lines a the CPR on the side of the engine block and clean the inlet and outlet with carb cleaner and compressed air. Retest, if still not in spec swap part with a known good part. After verification of proper control pressures we need to set baseline CO.

Being as all of the cars we got across the pond have OXS sensors we use a different method for setting baseline CO. We set the duty cycle of the frequency valve at 50% at idle, I believe you have no OXS sensor or frequency valve. If this is the case you have 2 choices, either find a local shop with an exhaust gas analyzer and set the tailpipe CO level to around 1.2% or "lean drop" the engine. Using a long 3mm allen key SLOWLY turn the adjusting screw in the airflow meter anti-clockwise until the idle bobbles. Then turn back in about 1/16-1/8 turn and see how it runs. This should get you a pretty good baseline.

Only after these basic checks and adjustments are performed can we start looking at other systems. Feel free to ask any questions, as an Audi master tech with many years at the dealer fixing CIS, I have them pretty much licked. It is simple system but certain key things need to be inline for it to function properly.

Cheers,

Dan

Gouldy · 27-02-11, 12:47 AM

thanks for the info there matey! , am going to get a new sensor for the car (bottom of the stat) and then get the mixture done, and work from there

fj1200 · 27-02-11, 01:48 AM

Forgot to mention, make sure the micro switch on the throttle valve is working properly. Unplug the connector, usually 3 pins and jumper the obvious pins leading to the idle switch, see if the idle simmers down.

18-02-11, 07:22 PM	#71
BIGGYIN 4 ring whore! Classic Audi Club Member Join Date: Mar 2009 Location: Merseyside Posts: 7,976	Well,that probally won't help. __________________ q90 B2 Type 85 - q90 B2 Type 85-PROJECT-ABY 20vt KARL. Injection is nice but I'd rather be blown

18-02-11, 07:23 PM	#72
Gouldy Senior Member Join Date: Feb 2010 Location: W.Somerset Posts: 1,083	will have a look in a min!! got to go out to the garage anyway, will check the readings hot and cold!

18-02-11, 08:00 PM	#73
Gouldy Senior Member Join Date: Feb 2010 Location: W.Somerset Posts: 1,083	i bloody give up!! volt meters broke now!! i unplugged both of the sensors on the stat housing and they made no difference however when i unplugged the ISV and plugged it back in a few times, it seemed to run a bit smoother , cant tell bugger all now the volt meter is broke

26-02-11, 03:16 PM	#75
Gouldy Senior Member Join Date: Feb 2010 Location: W.Somerset Posts: 1,083	just done some checks on the sensors the Thermo time switch when cold has a resistance of 32.3 Ohms the warm up reg when cold has got 21.3 the top sensor on the thermostat housing has 0 when cold and 35 when warming up (i think this sensor is just for the temp gauge???) and the bottom sensor on the stat housing is 0 ohms when cold and 0.1 when hot, however if unplugged the idle rises quite considerably, so it must be doing something? any ideas guys

26-02-11, 08:25 PM	#78
fj1200 Grown up member Join Date: Feb 2011 Location: Shrewsbury, MA U.S.A Posts: 21	Greetings guys. New to the forums, let's see if I can help here. First and foremost, we need to decide if the idle hunting is a function of the ISV circuit or fuel mixture. A lean fuel mixture will cause surge in RPM, the ISV may not be able compensate fast enough to cancel out the surge. You stated that the engine appears to be running rich when hot. If the control pressure regulator is not operating properly someone may have adjusted the baseline fuel mixture to run properly when hot, but still be able to start. We know the thermo time switch wiring was damaged and not allowing proper function of the cold start injector. I would start by repairing all wiring at the thermo time switch and then testing the circuit. Use a 12V LED with a 1K ohm resister in series with the positive leg of the LED. unplug the blue connector at the cold start injector and connect the LED to the harness. Crank the engine and make sure the LED lights up. if no light, test for 12V to pin 2 of the connector while cranking. If no power, then inspect all wiring at the starter closely. If no groung (earth?) then the thermo time switch may be faulty. After this circuit is sorted we move on to mixture control. The best first step is to find someone with a set of CIS fuel pressure gauges, control pressure cold should be around 25 psi and hot around 52 psi. Convert to metric as needed. If control pressures are not is spec. disconnect the 2 fuel lines a the CPR on the side of the engine block and clean the inlet and outlet with carb cleaner and compressed air. Retest, if still not in spec swap part with a known good part. After verification of proper control pressures we need to set baseline CO. Being as all of the cars we got across the pond have OXS sensors we use a different method for setting baseline CO. We set the duty cycle of the frequency valve at 50% at idle, I believe you have no OXS sensor or frequency valve. If this is the case you have 2 choices, either find a local shop with an exhaust gas analyzer and set the tailpipe CO level to around 1.2% or "lean drop" the engine. Using a long 3mm allen key SLOWLY turn the adjusting screw in the airflow meter anti-clockwise until the idle bobbles. Then turn back in about 1/16-1/8 turn and see how it runs. This should get you a pretty good baseline. Only after these basic checks and adjustments are performed can we start looking at other systems. Feel free to ask any questions, as an Audi master tech with many years at the dealer fixing CIS, I have them pretty much licked. It is simple system but certain key things need to be inline for it to function properly. Cheers, Dan

27-02-11, 12:47 AM	#79
Gouldy Senior Member Join Date: Feb 2010 Location: W.Somerset Posts: 1,083	thanks for the info there matey! , am going to get a new sensor for the car (bottom of the stat) and then get the mixture done, and work from there

27-02-11, 01:48 AM	#80
fj1200 Grown up member Join Date: Feb 2011 Location: Shrewsbury, MA U.S.A Posts: 21	Forgot to mention, make sure the micro switch on the throttle valve is working properly. Unplug the connector, usually 3 pins and jumper the obvious pins leading to the idle switch, see if the idle simmers down.