Brett Matthews

Can someone tell me what the sensor (?) on the top rear of an S4 intake manifold is, and what readings it should have?
There are a couple of connectors that are deteriorating. On the right fuel rail towards the rear, it's a flat 3 prong, and on the left front of the engine ahead of the left fuel rail, another flat 3 prong connection, that dissapears under the front of the intake manifold. What's this one go to??

Help!!
Working on an '87 S4

BC

Intake manifold temp. Closed circuit *I believe closed* into the cooling fan/flaps system.

gf261

The one on the top rear of the intake is the intake temperature sensor if I am not mistaken. The other two...haven't the slightest....

BC

The other two have to do with the knock sensors I believe.

Jim_H

3 Prong = knock sensors?

Brett Matthews

OK, in the maintenance manuals, it shows an intake sensor on the bottom of the air filter housing. But I guess S4 is on the manifold. OK how do I test it? As shown in the manual? Because I am not getting anything, infinite resistance, anyway I try.

colin505

The one on the right side fuel rail , and the one in front of the left fuel rail connected to the water bridge are the knock sensors. These cannot be tested without a Hammer or equivalent. But if they are shot your timing should be approx 5 degrees retarded.

The knock sensors are in the V and are pretty much inaccessible with the intake in place.

Brett Matthews

Thanks Colin, Jim H., and Brendan C.,
Don't know that they're shot though, just that the "plastic" of the plug connection fell apart in my hand! Literally!!! I'll have to replace 'em, just to keep the possibility of an inadvertant grounding from happening!

WallyP

The temp sensor on the top of the S4 manifold is to make the fans run-on after shut-down when the engine is really hot. It should be open except when hot.

John Speake

Both the 3 pin connectors are for the knock sensors. It's highly likely that the sensors themselves need replacing, as all the insualtion on their wires will have become brittle and fallen off. The ensuing electrical noise will then trigger the ignition retard at high loads.

If you require new 3 pin connectors (female) that are connected into the vehicle cableform, I can supply.

worf928

Below is an example of that about which John speaks. Note that one connector 'looks' fine. The other connector is totally fragged, but that for both the insulation is done-for.

Mongo

When this sensor fails, will the fans stay off after the car is shut off despite a hot engine? I get this paranoia now that my connectors could be fried because when my car is hot and the fans are running, the fans shut off after I turn off the car instead of staying on.

Brett Matthews

Thanks John Speake,
The male connectors on the leads from the sensors are the part that has disintegated. The female plugs still seem to be OK......

Thanks again Wally,
So I should be reading infinit ohms.... May I ask where, if it is still used, the intake air sensor is?

And yes, the insulation on both leads, is breaking off.

Brett Matthews

The saga continues;

Finally dove into the intake removal, and found one of the rubber elbows had cracked and dropped off one of those two vacuum ports on the bottom of the throttle body, the connection from the MAF to the throttle body has a large 1.5-2 inch through crack starting at the right rear PVC hose port, one specialty "Y" hose was brittle as heck, and broke off as we were trying to take it off the intake manifold.
Who knows how the idle speed actuator actually works? It is slightly open....
Yes, I now know I have an idle position sensor, so I can test it as well....
Who knows what else I'll yet find!
The knock sensors will be replaced. Lotsa hoses will be replaced. Think I'll replace that idle speed actuator too..... Anybody know where the secondary air valve is, located in the manual on page 24-216?
Brett
GADZOOKS! I may YET approach that fabled $3k a year maintenance cost! SHEESH!

worf928

To be pedantically correct - you have an idle/WOT switch not a throttle position sensor in the analog sense. The switch will tell the computer if the throttle plate is at idle or if it is open more than about 80%. No actual position information other than those two and the 'not' those two.

It may be stuck. The LH/EZK pulses the ROA/ISV with 12v to control the exact position of the rotor. Clean it up, spray some lube at it, and hit it with 12v and see if you can get it to go from full-open to full-close.