Is it possible to adjust the TPS on a 32V without removing the intake?
 

Hi folks,

First of all, is there a good test procedure for the point at which the idle switch opens on a 32V car? Mine opens after the throttle (at the manifold bracket) is pulled about 5mm. The reason I'm concerned about it is that I think that, with the extra air being supplied by the Murf kit, the idle switch open point is pretty much at the point the throttle needs to be for cruising at 3K RPM.

I'd like to try moving the point at which it opens back a bit so it opens as close as possible after the throttle butterfly moves off the stop. The switch, along with the throttle body itself, looks to be pretty buried under the manifold, though. Anyone know whether adjustment is possible in situ?

Thanks,
Paul

Yes, it can be adjusted in place, we just did mine Friday, but you have to have very skinny hands and a wrench with a bit in it to gain access.
not fun, but then again taking the intake off does not sound like a fun day either, and even more so if the hoses are old, just from a cost standpoint.

When I had a stock intake I replaced the ISV without removing the intake, it wasn't easy and I had to stand on my head.

Thanks Greg.

Now knowing it is possible, I went out and pulled the MAF and took a look down to see what would be involved. I had measured the "lag" at the throttle cable bracket before the switch opened as 4.58mm. However, looking at the butterfly itself, the switch really is opening just as soon as the plate moves from its stop... it's actually about 0.5mm of plate movement before the switch opens.

I would think that's probably OK. What do you think?

Thanks,
Paul

Rick:

I concluded that was not possible! Do you have proof? :)

I could at least see the ISV when I had the water bridge and oil filler off. Not sure I could have replaced it from there, but maybe.

You need to back probe the LH unit with the engine hot to see if it is making and breaking the idle switch.

SQLGuy: That's cheating! :) Oh, and I want to warn you.....DO NOT remove the coolant reservoir cap or you could end up like I did once, flushing the oil pan!

:icon501:

Hmm... you mean you've seen where the switch tests fine at the LH with the engine cold, but changes its behavior with the engine hot?

The problem I'm having is lean spikes, like the LH thinks it's in overrun, when cruising at 2 - 3K. Throttle is very light, but not zero, at that point. Have you seen a hot engine make the idle switch stay closed longer?

I think the easiest thing will be to hook up one of the SSI-4 channels to sense the idle TPS switch (if I can find a reasonable place to tap into that line). Hopefully the LH lets it float enough when it's not closed that I can read it without having to rig up an external pull-up and diode circuit. Anyway, if I can data log this, that will be the best answer to whether the lean spikes are because of false overrun triggering.

Yeah, and notice the coolant drops already on the top of the oil filler opening. Not a good sign.

I did something similar once on a motor that was already drained of oil. A nice gush of coolant came out of the bridge opening and went you know where. I resolved it by dumping 2 quarts of tranny fluid down the oil filler opening. It is a good detergent and water miscible. Drained that. Then finished with 2 quarts of oil and drained that. Argh!

Well, sounds like I maybe got lucky, but I didn't end up dropping more than two or three drops of coolant down the oil filler opening during this process... and all that's back together now.

I did have the lower radiator hose off and the bridge pretty well undone and drained before touching the oil filler bolts, though.

Cheers,
Paul

If the idle switch is right on the threshold (which is sounds like it might be) then it is possible that the idle switch is closing momentarily in very light-throttle cruising.

In Sharktuner, you can un-check the box that says "cut off fuel on deceleration" (Fuel parameters page)-- that avoids any transition issues-- either a cutoff when cruising with a light throttle, or a lag when easing back on the gas after decelerating.

:cheers:

Strange, I've been having a similar problem recently. I have a wideband O2 as well as the stock one, although my car is back to stock now (just an x-pipe). Every so often when I accelerate hard and shift or let off the throttle slightly, the wideband readout goes way lean (18-19) and I can feel the stumble. But I am WAY far away from the idle position. If I move the throttle back and forth a bit, it goes back to stoich. So, I have been suspecting a problem with the idle switch as well. But testing the switch just sitting with the motor not running does not show any erratic behavior at all. My plan is to attach a Sharktuner and drive around until I can replicate the problem and log it. It sure feels like it's inappropriately getting an idle throttle position reading. If it is, Sharktuner will show it and I'll replace the switch, even though it's only a few years old.

This is a simple continuity switch which goes open circuit versus ground once off-idle. You can tap it at pin 2 of the LH plug.