quirky idle problem
 

Been trying to get this problem solved. Had to turn the idle speed up just to keep it running. But runs normally driving. Hot runs very rough, colds the same but surges between almost stall and 1500 rpm? Changed wires, cap, fuel injectors plugs are good and a nice light gray. New battery and tested the throttle sensor and MAF sensor OK. Hoses look good from the ones i can see. Have another idler control valve but as a last resort as its a bigger job. Can't remember what the two things on the fuel rail do or how to test them? Any other ideas?

Try just unplugging the idle valve and see if anything changes.
Separately, try unplugging the O2 sensor.

Either part can cause a surging idle.

Tried the o2 sensor with no change. Will try the idle valve next. What should i notice?

Try removing the Aux Air Regulator and cleaning it out with some spray cleaner (or acetone). It worked for a little while until I replaced the unit.

You said you disconnected the O2 sensor but there was no change. When you do that the car should run richer and there should be a change. There's a short write-up in the manual or Clarks Garage about setting the idle with a jumper on the diagnostic plug next to the brake booster. Have you don't that? I'm wondering from what you've said if the O2 sensor is bad.

hpaulb:

Definately O2 sensor....
Later,

Bigger project because the 02 sensor will not come off even with any tool. Will have to remove the exhaust and either weld a long bar to it or drill it out. Unplugged should make it run smoother correct?

OK need to go into this again. Removed the exhaust system and put a new O2 sensor in. Thought it was better but not really. So it sat in the drivway all summer. Used it a couple times to go to the lake but had the problem of idle at a stop. The only thing i can do next is use me vacuum tested? Got a Star products TU-1PB from a friend but don't know how to use it. I can find a threaded port to connect it but not sure how to read it? Google shows me nothing. Anu ideas. After that i will take off the intake and replace the idle valve. I have a used one that worked before.

Is the throttle switch adjusted properly so that the contact "clicks" with throttle closed?
The switch may work fine, but if it's in the wrong location...:)

With the engine running get a spray can of carb cleaner and spray around the intake system and see if it changes running at all...would show you a vacuum leak location.
Don't forget to spray the intake-manifold-to-head joint as well.

I've used 10 psi air into the j boot with 2" pvc cap tapped for air hose. Then I sprayed the entire intake system with soapy water solution: Throttle body around springs and shaft, under the j boot and around all intake manifold to head junctions, All hoses and vacuum fittings. This has always served me well.

A smoke test is more definitive...
http://forums.pelicanparts.com/uploa...1480462306.jpg

Here is were i'm at as of last week. Idle has gotten worse and now very rough and stalls below 3k rpm

Parts changed from other engine:
Spark plug’s and wires
Dist. Cap
Injectors
Removed intake manifold, replaced idler valve and inspected vacuum lines and seals
Cleaned and tested air flow meter potentiometer
Replaced Throttle housing
02 sensor
Compression all four at 165
Leak down at 3%
Fuel filter about 3k ago but has been 7 years.

What does the Shutoff valve and control valve due?
Fuel pressure? anything is a guess at this point

Have you replaced the FPR (Fuel Pressure Regulator) on the rail?

No, don't have one and no parts places around. Have an update. Cut out the charcoal canister system with now change. Thought i'd try it. Seems to run well above 2k but not below. Someone must have something for me to look at next.

Don't you hate these? Have you tried disconnecting the throttle switch to see if that makes a difference? There's a way to fool the DME (at least on the early cars) and it works a treat but involves resetting the throttle-closed endpoint adjust and compensating with the air bypass. I ask because in reading your posts it seems the problem is worst on idle.

What about the small vac lines off the throttle body? Reversed?

Willing to try anything at this moment. I'll recheck the throttle body lines but i dought it. They seem to only fit in one place. Still want to measure fuel pressure and regulation but not sure were to get a gauge.

Check fuel pressure. A gauge is fairly cheap at napa or other FLAPS. I had to make an adapter by using a short pc of aluminum round stock and drilling/tapping both ends to fit the end of the fuel rail and my gauge. Do a search for more details - many guys have done it. Or you could just buy the gauge from one of the 944 suppliers. Look up what the pressure is supposed to be (30? or 40? something psi) and then see what yours does when it's running good or bad.

Vacuum leak - rather than just "inspect" you may have to use some pressurized smoke to find a problem.

If it's not fuel pressure or vacuum leak you may want to try another DME. I don't know the specifics of the 87 924S but I'm assuming it's similar to my early 83 944.

Good luck and keep at it.

Nobody around here to borrow a DME from. The 944 is the same as the 87 924s but not sure about older than 86? Latest is, this afternoon i retested the AFM and it still read correctly on the temp sensor and output resistance across the open to closed test is good at 2.6k to 3.7kohm. Problem i may have is i can't read the 5vdc on the cable pin 3 from the DME so that may be the problem?