Sasha

I am kind of at a loss. My idle (adjusted correctly) floats by 50-100rpm every couple of seconds. I had this problem ever since I bought the car from an impound yard. Since then I replaced:

- fuel pump and return check valve (new)
- fuel filter (new)
- fuel pressure regulator (new)
- fuel pressure damper (new)
- fuel injectors and seals (new)
- Cap, rotor and wires (new)
- Vacuum hoses (new)
- Intake manifold gaskets (new)
- Oxygen sensor (new)
- DEE (DME, ECU or whatever they call it) (from another working car w/o the same problem)
- Fuel pump relay (used)

Installed:
- cone air filter
- new aftermarket cat and exhaust

By looking at the mass airflow sensor (whatever it is called) needle under the plastic cover, the amount of air coming in stays constant, therefore, the MAF most likely is not a suspect.

The problem remains. It does not seem to adversely affect the performance of the car. I am thinking idle speed controller – big bucks for a little improvement. Factory manuals say there is a way to disable this device (by shorting terminals A and C on the diagnostic port). The pictures show the plug located near the battery (bolted to the side of the car with bolts just ahead of battery). I don’t have that! If I did a sure way to check it would be disable it’s operation and see what happens.

Any ideas of the problems itself or the diagnostic ports will be appreciated.

Thanks.

SoCal Driver

Ask what changes the idle. Air bypassing the throttle body.

Where can air bypass the throttle body? Any of the large and small vacuum lines that are on the engine side of the throttle body. Also there is a large o-ring between the throttle body and the intake manifold as well as an o-ring around the idle adjustment screw.

Why does your cars idle fluctuate? The DME is controlling the idle bypass valve and keeps trying to reset the idle. You can over ride this by jumping from pin B to pin C at the test plug. This makes the DME center the idle control valve. You use the large screw on the throttle body to set the idle.

With the idle control valve out of the loop see if your idle fluctuates. If it does then start thinking vacuum leak. Possibly the brake booster fitting or any of the other large vacuum hose connections. Don't exclude the o-rings.

Sasha

SoCal - thanks for reply. I recall now, that when I move it just right, I hear the hissing sound where the large hose connects to the brake booster! How easy is it to replace that fitting?

A sub-question - where is the diagnostic port? My car seems to missing it, but I have an empty plug near the firewall ziptied to the engine lift point - is that it? if so how do I identify terminals A and C. Thanks.

SoCal Driver

Test plug.

Sasha

SoCal,
I have seen this picture in the factory manuals. I can't find the port anywhere! Could you point the location of it on the car. I looks like battery compartment, but apparently not.

Sorry to keep asking, thanks.

roy_josef

It's located near the brake booster on the left (driver's) side of the engine compartment.

SoCal Driver

Looks like the drivers side fender well just in front of the hood strut.

I'll check.

Any one with an 87 know where the plug is?

Sasha

I went and looked at the car - and it is neither on passenger side nor by the brake booster. Anywhere else it might have been?

Thanks.

RJB

Sasha,

The connector is on the fender of the driver's side by the brake booster. You might be overlooking it because it has a plastic cover over the top of it and it does not look like the picture until you pop off the cover. It is hinged and the plastic is old, so pry it up carefully. At least this is where mine is on my '87 and I had a hard time locating it the first time.

SoCal Driver

Rodney to the rescue!

Sasha

Thanks a whole bunch. I did see it - you are right, Rodney, it doesn't look like a anything electrical , but rather vacuum related. What an exotic place to put a diagnostic port....

Thanks.

SoCal Driver

Jumper the B to C pins and run it for a while. Like to know if the problem persists.

SoCal Driver

Just re read your opening statement. You imply the idle was adjusted properly. How did you do that if you didn't jumper the pins on the plug?

Sasha

I didn't adjust the idle, a local shop did. I did mess with the adjustments on Air Flow sensor. I think I put them back where (the same) local shop had them after smogging the car. I just assumed, the idle is adjusted properly because I trust the shop (Prescision Motion/Kravig Engineering in Riverside, CA). I do know how to do it now after reading the manual. I think the BS with O2 measurement is just for emissionsions. If I had to do it myself, I would just bypassed the idle stab. and adjusted the idle by ear and tach in the instrument cluster. I would then lean out the mixture as much as I can w/o adversly affecting the performance.

Thanks.

SoCal Driver

You live in Riverside?