firemn131

So, I am just starting to dial in the quadrant cables. after complete engine\intake overhaul along with a borrowed ECU.
The only engine on time so far has been the initial break in.

I rebuilt the complete intake to include throttle plate, flappy, new ISV etc..

Engines starts right up but idle is soo low that I have to manipulate peddle to maintain. When I use the pedal to idle at 600-800 it runs smooth. I doesn't appear that there are any vacuum leaks.
TPS is adjusted correctly with slack in pedal cable. Bowden feels ok. My urge is to adjust the peddle but I understand this may be counterintuitive to TPS proper function.


I understand two ways to adjust.
1. Adjust TPS with cable then Bowden then Peddle.
2. Peddle, TPS, Bowden.

So questions..

Will it take a while of running for the ECU to adapt and correct with a consistent idle?

Should I adjust peddle to keep it running until ECU learns then start over?

I set the throttle body\TPS up on the bench and pretty sure I got the stop for idle set dead nut along with the TPS on off.

I really don't want to take this intake off if the ECU and peddle adjustments will dial it in.

Thanks

FredR

John,

Your symptoms suggest to me that maybe your ISV is not working for whatever reason. Have you checked at the LH plug that the idle switch contact change is registering there?

jcorenman

The throttle has a mechanical stop, part of the spring-cam mechanism. If you had that apart then it is very likely that the mechanical stop got misadjusted and the throttle plate is not open far enough at the stop.

The idle is controlled by the LH ECU. Attempting any other adjustment (pedal, cables, etc) will only result in frustration and a car that won't idle reliably. The airflow for idle comes from three sources: The slightly-open throttle plate, the brake-booster venturi on the driver's side of the intake, and through the ISV. If the throttle plate is not open far enough by the stop, then the ISV will not be able to provide enough air for idle even when the LH opens it fully. (Conversely, if the throttle is open too far on the stop, then you may have a high-idle even if the ECU closes the ISV completely.

What you want is for the throttle to be open far enough to idle with only a small contribution of air through the ISV. Then when more air is needed (e.g. hot intake-air temps), the ISV has plenty of headroom to open further. (And of course, make sure the ISV is connected properly).

It is possible to adjust the throttle-stop without pulling the intake, and that's important because it is going to take a few tries to get it right. Remove the airbox and MAF, find the stop-screw and loosen the locknut, advance the screw half to one turn for starters, reassemble and test. There may be a feeler-gauge spec somewhere but I haven't found it.

There are two other methods of getting more idle air: one is to drill a hole in the throttle plate, start with 1/8". And be sure to clean up the schwarf. The problem with this is that IF it turns out to be something else, then you've got too large a hole in the throttle-plate.

The other idle-air path is through the brake venturi, the hole through that is around 1/8" IIRC. Get a spare (used is fine) and drill it out to maybe 3/16". I wouldn't go larger and there is potential for reducing engine vacuum to the booster so this may not be the best idea, but it worked well for me-- and is reversible with a replacement venturi (although new ones are not cheap).

firemn131

Wow,
gotta digest this

firemn131

I have an extra venturi.
It seems drilling the hole, would make troubleshooting much easier. If that doesn’t work I can then decide to tackle the adjustment. Can you describe where I would drill this hole?

FredR

Does the idle stabilise at around the correct rpms after the motor is fully warmed up or do you still have to fether the throttle to hold the idle?

jcorenman

Like this:

firemn131

Ohhh,

thanks Jerry.

Weather was terrible and I didn’t feel like shooting blind.
I never let it warm up as I knew I had pedal adjustments to make.
ISV worked on the bench (new).
will check that if venture surgery doesn’t work.
Thanks gents

FredR

John
The zISV is designed to support a more or less normal idle with a warm engine and no ac running. Without a functioning ISV on cold start you have to fether the throttle until it warms up. Once warm no need to fether but stick the ac on and it will dive or die completely.
If the signal from the LH is not hitting the ISV it will not work of course. If the problem is not related to the ISV then Jim has given you a good synopsis. Personally I prefer to eliminate the easy to do things first.

firemn131

I think I will do the ISV check and then Proceed from there.

There is so much peddle required to sustain it that Ian thinking I won’t be very lucky.

firemn131

Now that I think about it I don’t think there was any opening for the throttle plate. I will try ISV voltage first and then go from there. I have a spare throttlebody assembly I will see how to practice adjustment if ISV checks out.

Kevin in Atlanta

I would look for another LH to swap in before doing anything else.

I think the hybrid chip is iffy.

MFranke

I agree with Kevin. Swap with a known good LH, and rule that out. Low idle was a symptom for one of my cars, which then progressed to stalling, and then no start. It was the LH.

firemn131

I am using my spare LH from my 89.
the 87 proved to be an issue earlier.

car is in the garage with more weather today. I may run an exhaust tube out.

i just got the drivel connected and still need to finish topping up the transmission and PS.

firemn131

Kevin Nailed it!!

ECU fail.

I went out this morning to look over the vaccuum holes in the top and bottom of the fuel control. They looked to be correct. Disconnected throttle and cruise cable.
no start.
reconnected all, No start. with a back fire.

Checked timing to make sure i hadn't skipped a tooth, swapped ECU into its original position (89 auto). No start.

Either a failing ECU was the idle culprit or just coincidence.

And again, I wait for ECU to be rebuilt or buy another.

At some point this car will drive.


Appreciate all of the input.