Hi,
1985 GSL-SE
Cats removed by previous owner. Leaks around the muffler. All stock car, but new to me.
The throttle surges between 1100 and 3500 rpm. At any given throttle position, the surge is the same duration and about 500 rpm jump. It surges faster at lower rpm (about every 2 seconds), surges slower at high rpm (about every 3 seconds. The surge does not occur at any rpm when I disconnect the TPS.

What I have done:
1. Replaced all the vacuum lines under the hood. There are no vaccum leaks anywhere. All intake gaskets are good.
2. Thoroughly cleaned the throttle plates, intake plenum, air flow meter, BAC valve system, throttle linkage, dynamic chamber. Cleaned out many electrical connectors. Ran a bit of SeaFoam through the intake. All seems very clean.
3. Changed plugs, rotor, wires.
4. Cleaned out the clutch switch and confirmed operation.
5. Checked all of the underhood solenoids using Haynes and factory service manual methods.
6. Checked compression, but poor man's style by using my fingers over the plug holes. I strongly believe compression is high, she starts easy, sounds strong. Plenty of power.
7. Checked and load tested the battery. All ok.
8. Adjusted TPS. The TPS resistance changes steadily throughout the plunger range, I think it is behaving just fine. TPS position does affect engine rpm.
9. Timing is good. Vacuum advance at distributor is good.
10. No red dash lights.
11. Changed fuel filter. No effect.
12. Adjusted dash pot.
13. Read every post I can find about idle surge, but find nothing about throttle surge.
14. Cleaned injectors and replaced seals.
15. Exhaust is not excessive, too white or too dark.

Detailed symptoms:
Cruise does not work, may be related. I have not checked all of the cruise circuits.
The clutch switch does not cut ignition, has no effect, car will start in gear.
She starts no problem, revs high to warm up like supposed to. As the engine comes down in rpm from cold start, the surging will begin and continue until just before steady idle at about 1000 rpm (by the instrument gauge). I cannot get the idle to go any lower using any adjustment process. At 1000 rpm, there is no surge and she purrs smoothly.
The vent and vacuum solenoids work via 12V and blow test, and they both get constant voltage with the car at normal temp. It's as if the computer does not tell them to operate except to stay open (vent) and closed (vacuum). I have checked all of the input devices to the control unit (assuming it's the main ECU) except the neutral switch due to difficult access under the car and I don't know where a connector is located on the other end. Same story with the 5th switch. And I don't know where the ignition pulse comes from.
Since the TPS does affect the rpm, the control uit is sending a signal.

The questions:
Could the untested neutral switch be a culprit? Other secret gremlins anybody suggest?

Sneak in an exhaust question, what are my options to get a properly operating exhaust system? The shops around me don't have a solid answer. Just a new cat converter and muffler?
Thanks.

 

The air control valves move, the auxillary acutuators move. The actuator shafts are steel with a flexible rubber section in the middle. The shaft was broken at the rubber part on the front shaft. So the shaft was turning, but the auxillary port in the front was actually stuck wide open, adding way too much air into the intake system.

I will commit to taking off the rest of the intake tonight to expose both auxillary port valves, cleaning them up and hopefully they will turn freely.

A very sneaky problem that I hope does not catch anybody else.

 

throttle surge update, problem not solved. Fixed the aux air port and now it moves freely. But the problem is not in this area. All the air control valves are working. I'm stumped again. No response anywhere, I hope for ideas!