Gary Knox

I have been "fighting" a somewhat sticky idle control valve on my '89 S4 for the past couple of years. The car has a chip, and the idle has been in the 1050-1100 range for essentially all that time. It isn't a big problem, but it does not give the engine braking effect that I'd like - especially on the highway (only drive it to, from, and on Watkins Glen and Virginia Int'l tracks).

I have used PB Blaster, Kroil Silicone, and Kroil Penephite in rattle cans to spray into the snorkel/hose that disconnects at the throttle mechanism on the left side of the intake. I always spray into that snorkel for about 5 seconds or so using the tube that comes with the penetrating fluids, plug the hose to the intake from which the snorkel was disconnected, then start and run the engine for about 5 seconds to draw the solvent into the ICV. Let it set for a day or so, then start it up and "hope" the idle has dropped down below 1000. For approximately 2 years (and ~1800 miles of highway driving, ~700 miles of track per year it has NOT done so).

A few weeks ago - and a few days before I headed up to Watkins Glen for my second DE of '12 (3 months since the last DE with the car rarely being started), I was looking at my "solvent shelf", and decided to pull the "Corrosion Block" can off the shelf. Normally I use this only for to treat electrical connections whenever they are re-connected in any service work I do. But - I thought "what the heck - how can it hurt???", so I performed the same process with this solvent product. Did it again 2 days later, which was one day before my departure. I wasn't surprised when I left for the Glen, and there was no change in the idle.

BUT - after about 65-70 miles of rural road driving, I took my foot off the accelerator as a traffic light in the distance turned red, and to my amazement, the sound from the muffler was distinctly different, and the instant MPG readout was 90! For the next 190 miles of highway driving, for 2 days on the track, and for 255 miles driving home, the ICV worked flawlessly. Idle is constant at ~925 now at cold startup and at full warm engine temperatures.

I'm only relating my experience. What caused the corrosion, coating, or whatever to be removed??? It may only be circumstantial and an old wives tale, but I'm convinced the Corrosion Block product had a much more significant effect than I'd been able to achieve with any of the previous products I'd been using.

Might be worth a try if you have trouble with the ICV!!

Gary Knox

Mrmerlin

Gary have you ever has the MAF rebuilt? This could also be a cause of the higher idle

Gary Knox

Stan,

I haven't had the MAF rebuilt, but I cleaned the wire within the past 2K miles. And this MAF has about 75K miles on it - it is not the original on the '89.

Gary

Mrmerlin

I would get a MAF rebuild done for your car

WallyP

"...I took my foot off the accelerator as a traffic light in the distance turned red, and to my amazement, the sound from the muffler was distinctly different, and the instant MPG readout was 90! "

Sounds as if the problem was the idle switch, not the ISV. The ISV has no effect on the mileage readout - the idle switch does. If the idle switch isn't working, the ISV won't work either...

nc_growler

Wally, please say more on the idle switch. Can this be tested to confirm it is working correctly?

928Myles

nc_growler
Dwaynes excellent write-up on intake R&R gives instructions on checking & adjusting the idle switch.

There should be an quiet but audible 'click' just after the throttle moves from closed and just before it returns to the same.

Others will chime in with additional test proceedures (electrics).

Myles

nc_growler

Thanks Myles. I've got the link to Dwayne's write-ups. Will do some diving.

66% of the time, I get that nice engine breaking Gary is talking about.

Top end R&R done by PO. Haven't done the MAF rebuild yet... 74K miles.

WallyP

For those who have the digital dash, checking the idle switch is easy...

Get to a road speed of over fifty mph. Put the info readout on instant mileage. Lift your foot completely off the throttle and watch the mileage.

If the switch is not made (not closed, not functioning correctly), the mileage will be perhaps 50-60 mpg.

If the switch is made (closed, functioning correctly), the mileage will go to 90mpg and stay there until the engine speed drops below about 1500rpm.

nc_growler

Wally, I have digital dash and this is exactly what I've been experiencing.

Looks like a real idle switch problem.

928Myles

nc_growler
if the click is still there when moveing the throttle by hand then yes - you have a real problem. If it is not there then it may just be an adjustment issue. Unfortunately I don't think these can be adjusted easily with the intake in the car - hopefully I am wrong.

Myles

928Myles

For those of us dwelling in metric countries:
When you try Wally's proceedure (digital dash) the litres per 100km readout should go to 0.0.

Myles

dprantl

If you are going to try the deceleration idle switch test, make sure the throttle cable is adjusted correctly and make sure the throttle closes all the way.

Dan
'91 928GT S/C 475hp/460lb.ft

Cheburator

Holly thread resurrection, Batman!

I am not sure Wally's test procedure is 100% correct.

I hear a click from my 1993MY GTS 5-spd throttle switch. But the car had really bad idle when I bougth it. Sprayed a lot of contact cleaner inside the hose to the icv and hey presto, idle back to normal. However, it takes a while for the ICV to start functioning correctly i.e 90mpg and usually happens when the engine is fully up to temp.

My line of thinking is that your throttle switch may work, but if the ICV is gunked up, it would not be able to operate correctly, thus not getting the 90mpg reading and proper engine breaking...

Or have I got this completely wrong...

Alex

Mrmerlin

from Wallys post

Sounds as if the problem was the idle switch, not the ISV. The ISV has no effect on the mileage readout - the idle switch does. If the idle switch isn't working, the ISV won't work either...