datz

im having a hell of a time diagnosing my idle problem, it surges at idle, drives fine but surges at idle.
ive replaced all vac lines and intake gasket and tested several times for vac leaks.
ive cleared out the lines to and from the thermowax and made sure the thermowax/fast idle cam works fine.
replaced BAC, AFM, TPS, and TB.
adjusted the TPS probably like 50 times from .6v, .7v, .8v, .9v, 1.0v, 1.1v, 1.2v, 1.3v, 1.4v 1.5v, and 1.6v cause ive heard 13b's all like a little different setting.
theres a code the ECU throws for the fuel pump resistor relay, but i bypassed that with jumper wires, and still surging.
the car is a 90 GXL with mufflers welded on and a homemade CAI, with the CAI the AFM sits a LITTLE pointing down but level in any other demension.
while backprobing the ECU connectors the pin for the clutch switch has no voltage with the clutch deppresed or not, so i then tested the actual switch and clutch depressed shows .9 ohms resistance and not depressed shows 0 ohms. so my question is if the ECU doesnt see a signal from the clutch switch, NOT the cutoff switch, will the ECU act funny and tell other sensors and whatnot to do their job incorrectly, or would replacing it just be another waste of money since i drives fine?

AGreen

iTrader: (11)

Warm up car and disconnect BAC at idle. Most voltmeters have a %duty cycle setting. My $20 craftsman one does. Probe the BAC connector with both leads. The duty cycle should be steady. Plug it in and backprobe the connector and see what it reads.

Surging at idle is generally a TPS or timing issue. Are you SURE. 100% SURE that you set the TPS properly? It should be at 1.0v exactly. Engine warmed up, throttle shut. I'd say check timing, but you need a steady idle to do so. Broken record here, but vacuum leaks are the other cause, but you said you've searched and searched for them. How about air leaks between the AFM and TB? Try cleaning the gunk out of the TB.

Also, it's not the clutch switch, I'm pretty sure it's the neutral switch that inputs to the ECU. My TII surged at idle in neutral, but not in gear. Set the TPS and everything was golden.

datz

i know you cant properly adjust the timming without a steady idle so i loosened and turn the CAS almost every witch way, advanced and retardted, startin and idleing for about 10 mins but every adjustment then engine running seemed like it made no difference at all. so im thinking the ECU is ignoring the CAS input or the CAS is bad( but it tests fine)

the clutch switch and the neutral switch are both input devices. plus it will surge if in gear or not as long as its at idle. when i switch on the A/C and blower it stops but then it starts surging again a few mins later or so.

wouldnt and air leak between the AFM and TB cause vaccum, so the carb cleaner or propane would suck into them and cause the engine to speed up??
my air filter is not the tightest fit on the input to the AFM, if thats leaking could it cause vac leak?

AGreen

iTrader: (11)

Yes, but most likely not vacuum. Unless you have some seriously restrictive intake, there shouldn't be a vacuum until after the TB. Loose filter wouldn't cause it.

How long's it been doing this? Did you do something to the car and it started, or did it just happen one day without warning?

satch

iTrader: (1)

Injector grommets can also create leaks over time. And does your bouncy idle occur regardless of how long you drive the car or does it improve as the car warms up completely ?

datz

i bought it and it idled fine, then i check almost everything and made sure it was in accordance with the FSM and now it surges.
and yes it surges no matter hot or cold.
this is driving me ****** nuts!!! pardon my french!

datz

does the clutch switch even matter, can i bypass it and do without?
since it has 2 switches on the clutch pedal?

AGreen

iTrader: (11)

The only thing I knew the 2 switches were for was that one (bottom) is a starter interlock, and the other (top) disables cruise control.

pfsantos

iTrader: (1)

^ sounds about right. Don't have the FSM at work (USB stick effed up), look at the ECU wiring diagram and see if the clutch switch is one of the inputs. You can always unplug the switch and see if it changes anything...but it most likely won't.

You said you checked the thermowax/fast idle assembly. Did you make sure the cam disengaged from the throttle pin? You can adjust this, btw., but I generally just do the following:

Warm up the car fully. Then take a long screwdriver, and press down vertically down on the part that the thermowax plunger pushes on. If the throttle plate closes a bit more, it wasn't releasing the throttle completely. I usually adjust the timing while pressing down on the fast idle assy. to make sure the throttle is completely closed.

edit: FSM in sig. link...check the wiring bit.

HAILERS2

About the clutch switch and backprobing the ECU.............................you should have read approx 12v with the clutch disengaged and lower than 2vdc with the clutch engaged.

The reading of 12vdc with clutch disengaged...........voltage you read comes from a device inside the ECU.

The reading of less than 2vdc with clutch engaged...........you put a ground on pin 1Q with the clutch engaged and that drags the 12vdc down to less than 2vdc.

Pin !Q is, counting from the right to the left, the ninth pin on the top row. Make sure your backprobing it and making contact with the wire. The plug MUST be connected to the ECU for this test.

Then again like the man said, if you disconnect the clutch switch at the clutch pedal that is the same as letting off the clutch pedal.

Two switch assy on the clutch pedal. One is the interlock switch at the very top. The lower switch has two electical plugs on it IF you car also has cruise control. One of those plugs is dedicated to the cruise control and the other plug sends a gnd signal to the ECU pin 1Q to let the ECU know your now putting the transmisison in gear.

Your problem is probably not the clutch switch. Could be a vacuum line routed to the wrong place or another good one was mentioned in that if the lower grommets on the fuel injectors is hard as a rock and leaking air thru it, then the idle will be crummy but run good at higher rpm.

1Q is the pin on series five ECU NOT series four ECU.

datz

you im gonna double check that i dont have a few vac lines swapped (even though i paid good attention while replacing them, i could of happened!)

and satch, i got new injector grommets for the secondaries but not the primaries (but when i use a tube and spray a bunch of carb cleaner under the VDI manifold theres no change in idle speed, so i dont think their leaking.)