Proper way to clean the sensor plate

Sunroof · 11-21-2001, 05:50 AM

Before I take off the air boot and possibly screw something up, I was hopeing someone can pass on first hand experience on the proper and effective way of cleaning a CIS sensor plate.

I am not sure just how delicate these are or how much force or pressure I can apply during the cleaning process. Nor do I know just how flexible and easily damaged a plate and adjustment points can get.

Okay, so I begin with taking the air filter and air boot off. Will that give me sufficient access to get to the entire plate? I am leaving the fuel distributor and the airbox attached.................can one of you wonderful Pelican heads take me from there please..........

With gratitude and wishes for a super turkey day.........

Bob
'73.5 T

Jdub · 11-21-2001, 06:06 AM

First off, I lust after your car. But we'll leave that for now...

Sensor plate should be cleaned very, very carefully, but you will be fine on this operation. Remove the airbox, then plenum (air boot), and peer down into the mystery that is CIS. Note any buildup, and gently spray some Simple Green or equiv. non-killer chemical onto the plate, esp. at the edges. Supporting the plate from below and lifting it very gently, take fresh paper towels and wipe up everything with great care. Clean the plate itself only with full support of the hand on the underside.

Turning to the underside, Gently push the plate up and then go with a bit of gusto at the edges, then on the underside of the plate as well, again with gentle firm support. You get the picture; support that plate.

Any questions on if you screwed up the plate position requires a look at the manual and a reset of the plate. I have never done this but I am told it can make a world of difference. That sensor plates come out of alignment at times, resynching them is a breeze I am told, but...can't speak firsthand on that one.

Now take a look down the throttle body, where the butterfly valve is (i.e. other end of the plenum connection, where your idle speed screw is). Spray copious amounts of Gumout of similar down there.

You car will run like crap when you first start it. Be prepared to take a short spin and run the crap out. Also, the sensor plate height is dicated by many things, but one is the plunger. That item is best left to a nice Techron run as this can free it up nicely. Also note how your sensor plate comes down after pushing it up: nice and even or with sticking qualities?

Jw

Sunroof · 11-21-2001, 09:06 AM

Thank you kind sir for your response. I have a wild up and down idle during cold start and one of the suggestions was to clean and adjust the plate, which I am sure it needs. It looks easy enough to do and I will give it my best. I have heard that too much cleaner down the throttle throat can create a hydo lock, but I would think it would take copious quantities to get that far.

Your procedure sounds simple enough and it is a good chance to check the air boot for cracks or age as well.

Always nice to know, folks are nuts about the older models. Maybe its just a nostalgia thing. But then again for me I grew up loving the 911's since I pulled up next to one in my Triumph TR-4A back in 1967. Seems to me, more folks want to move that way. As much as I love the "T" their are days I would gladly swap for an SC.

Regards

Bob
73.5 T

john walker's workshop · 08:02 AM

i've often wondered why there was so much ado about cleaning sensor plates. they get a bit oily from normal operation, but that would not affect anything. the position of the plate, under fuel pressure, and free movement are the important things. the wild idle is usually the warmup regulator allowing the engine to run too rich thru the warmup period. the original units have been superceeded to a later style.

Sunroof · 11-21-2001, 10:49 AM

John.
You may have hit the nail on the head with this one. My mechanic just reset everything and adjusted the pressures in the WUR, which by the way was a newly purchased original unit I found on a dusty shelf here in Atlanta. My mechanic did say it was adjustable! The up and down idle will go away once I am warmed up (160+) which takes awhile. I have to drive with the throttle level in the partially pulled position til then. If I lower it too soon, the jumping starts and the car will sometimes die. Once warmed it runs great.

Solution? Adjust to the lean side? Or have the WUR pressures reset? Is it possible I am not getting enough electrical current to the internal expanding lever?

Thoughts please

Thanks............
I like the frog!

Bob

john walker's workshop · 08:02 AM

the original is the one on the right. is that the one you have now? never had much luck adjusting the originals. they have been updated to the other style. the middle one has had the adjuster installed. to lean it, so it doesn't surge, turn the nut (not the bolt) clockwise, while the surging is happening, until the surge is gone. you can see the pin on the left unit. to do the adjustment thing, drill a hole dead center in the pin, 8-10mm deep, for either a 5 or 6mm bolt or stud, thread it, and install the bolt or stud, nut and washer. if the engine is real doggy w/cold, tapping the pin down will improve cold running by richening the warmup period. often they will go down too far, and a surging idle will result, requiring the adjuster modification to pull the pin back up a bit. this will not affect the hot running unless you get real carried away.

Sunroof · 11-21-2001, 12:54 PM

John...
I do have the one on the right. My mechanic made adjustments but I am not sure where. Without buying a newer unit is their anything I can do to solve the existing problem? One thing I did note was that if I lift my throttle lever up abit the surging goes away til the WUR does its warm up. I guess I can live with this for awhile, but it would be nice to do whats proper. I find it amazing when the engine reaches warm up (160 on my meter), everything is just fine. How did Porsche deal with this problem on the early CIS models or before a revised WUR was available?

Thanks

Bob

john walker's workshop · 11-21-2001, 01:30 PM

bob, the early CIS cars needed the hand throttle, so they would idle cold. they didn't have an air regulator to do it automatically. the surging is not normal. are you sure the hot idle mixture is no more than 3.5%? too rich hot, makes them even richer cold, causing an up and down, repetitive surge thru the warmup period.

Doug Zielke · 11-21-2001, 04:54 PM

John,
I'm sure the car ran much better after you removed the frog!

Jdub · 12-10-2001, 08:11 AM

Went through the cleaning process this weekend as I had some suspicions about gumming up the works...

In all events, thought I would add here that, when you remove the plenum, there are two hoses attached at the back. The one to the right (pass.) side is easily removed, but the one directly on the back is a bear.

To remove the tough one, unscrew it instead over at the right side of the engine bay, next to the oil tank, where it connects to the oil tank hose. Doing this lets you drain whatever muck might be in the hose and clean it up a bit. You will need to negotiate the plenum out over the airbox (SC here...) with the hose attached; easy enough to do.

Jw