Okay,
Most of you know by now that I'm restoring an '87 TII. This is a bit of a long post, but I hope ultimately worthwhile.

I've been studying the Idle problem threads for several weeks now, and think I've got a pretty good handle on the issues which whack it out. My problem is it won't idle below 1500. Otherwise runs well, although seems to guzzle too much gas.
Last weekend I dis-assembled the top end and spent time making sure that everything on the throttle body/UIM measured per the Haynes manual.

Things I discovered along the way:

The wire to the O2 sensor broke when I touched it - right where the wire from the harness enters the connector. I had an old harness off an n/a engine and replaced the wire/connector.

The connector to the BAC was damaged from the heat and likely not connecting properly - pins pushed way down in the connector plastic. Old harness to the rescue again.

Air pump checked OK.
Intake Manifold Check Valve checked OK
Air Control Valve checked OK
Air Supply Valve measured OK
BAC Valve checked OK - proper meter reading and click when energized with 12v.
Air Bypass Valve OK.
All of the solenoid valves on the rats nest checked OK

Water Thermo Valve checked not okay - would not open at any temp.

Fast Idle Adjustment was way out - set it according to the manual

TPS measured almost 1200ohms at closed throttle 4440 ohms at WOT - set it to 1000ohms with closed throttle (OK now).

Dash Pot was out of adjustment - set it according to the manual


Upon re-assembly, I discovered a significant split in the intake plenum hose right where it attaches to the turbo inlet and, also, the clamp didn't hold the hose tightly - so this could have been the original source of the fast idle. I removed the plenum hose and repaired it with hi-temp RTV and a new clamp.

Upon startup it ran at 1200 rpm untill warm then dropped down too low to keep running. If I held the throttle slightly open it idled fine - 800rpm smooth as glass.

I removed the Intercooler and checked the TPS with my meter and it read 670 ohms. I re-adjusted it to 1010 (close as I could get to 1Kohm) and checked that it would consistantly return to 1010 ohms with throttle action.

Re-assemble and restart. Idle is almost perfect. 800 rpm, but slightly un-steady. As I let it sit idling, it seems to run a bit rough - I can hear it miss occasionaly. While idling, it'll drop to 600 for a moment then back to 800. Also, the idle just doesn't seem as smooth as it was when I was holding the throttle open in the previous action. Just not solid.

Other stuff of significance done previous to this time:
Replaced all the rubber on top of the engine - all vacuum and fuel lines
Replaced the o-rings on the fuel injectors.
Replaced sparkplugs
Replaced Spark wires
Replaced the O2 Sensor
Replaced the fuel filter
Replaced the Pulsation Damper
Installed dedicated grounds on the Pressure Sensor, Ignitors and the problem ground on top of the engine - per grounding threads here.

It's been idling while I write this (I have a computer in the garage) and I stopped for a moment to check the tach:
Fairly steady at 700 with momentary rise to 800. Occasionally, it will stumble and drop down to 600 then back to 700.

I would sincerely appreciate your thoughts on what could still be up.

Thanks to all for your help in the past, and once again now!


- k -

 

One area to consider is looking at the exhaust manifold. If there is any kind of cracking (in your case a small one) then this can play havoc with idle. I had this problem with my car. It only showed a little dip in the rpm band at idle. Over time it gradually got worse until I had to keep my foot on the throttle at every stop or it would stall. The manifolds are prone to craking too.
Something to think about.

 

another thing to check, the Haynes manual sais nothing about this so check the FSM for your car. in front of the pressure sensor on the right shock tower is a adjustment screw (capped), it is called a 'variable resistor', it changes your idle mixture and if it is a ways out of adjustment it will cause idle problems. the FSM gives instructions on how to set the mixture of the screw.

GL

 

1st step:
buy Haltech;
perfect idle all day everyday.

 

I am regurgitating what my tuner told me about my idle surging the other night. The CAT is plugged or on the way. Hope this helps.

 

HOWEVER if it looks like this has never been tampered with then leave it alone. It only affeccts idle mix anyhow, and unless you have an exhaust gas testor you will only be guessin at best. They almost never need to be touched unless some other fool had played with it.

You sound like you are gettin close now, maybe some final TPS adjust, have you reset the computer?

 

How do you reset the computer?

 

General concensus is resetting ECU has no effect on anything . I was asking in this case if you had tried resetting it as I am monitoring if it does really at all effect anything.

I am one that possibly thinks it can eliminate some probs(I am a computer tech and reset computers all the time but different kind ) when an engine has been running on faulty switches and solenoids and injectors.

Do a search for info.
heres one
https://www.rx7club.com/showthread.p...reset+computer

Again was curious more then anything...

 

everything, every little bit of what your saying about idle. i'm going through. it bugs
the **** out of me. try this : if your cruise control cable is still connected to the TB
dis-connect it and then adjust the 'real' throdle cable on the back of the engine.
while it's running pull lightly on the cable @ where the support fork is and see what happens. i don't know if my throdle cable is shot, but it changes my idle a bit. or the support fork flex's. or maybe if i were to lube the cable, i'm doing that today. but maybe adjust the position of the throdle cable in the support fork using the 2 nuts
on the cable either high or lower and see what happens. i've left the cruise control cable off for now untill i get a hold of my idle problem. also all of the wiring on the engine is so brittle it bugs the **** out of me. i to am restoring a 87 turboII and these things are touchy, aren't they ? i'll be watching your progress..

 

The TPS has little to nothing to do with the idle of the engine.

There is not a thing wrong with adjusting the Variable Resistor for the idle mixture. If timid about this.....measure the output of the variable resistor at its output wire with the key to on. Write that down. Now play with it per fsm or your own method. You can always return it to where you started from by adjusting it til it reads the value you wrote down. By the way, RX like to idle rich. In the 13afr range. Anything leaner and it will pooh, pooh, pooh while idling.

Have you considered that the anti-afterburn valve inside the ACV is leaking air into the intake at idle??? The only part of the acv that ever feeds air into the intake is this anti-afterburn valve. After years of use ....they leak some. Disconnect the hose b/t the airpump and airfilter and spray some starter fluid into the hose. IF the valve is leaking......the idle speed will pickup a bit....indicating leakage. If it is leaking internally, you can block off the output hole for the anti afterburn valve with some rtv and about thirty minutes or so of time.


Haltech to get a idle? My royal ***. B.S.

 

Hailers wrote
"The TPS has little to nothing to do with the idle of the engine."

Huh? you have got to be kidding right?

 

If the hose connecting to the air pump is a bit loose would this qualify as a "vacuum leak" resulting in the car's inability to idle?

 

Hailers wrote (btw I respect your opinions just about everytime I read something by you but am confused on the last 2 things)

"There is not a thing wrong with adjusting the Variable Resistor for the idle mixture. If timid about this.....measure the output of the variable resistor at its output wire with the key to on. Write that down. Now play with it per fsm or your own method. You can always return it to where you started from by adjusting it til it reads the value you wrote down. By the way, RX like to idle rich. In the 13afr range. Anything leaner and it will pooh, pooh, pooh while idling."

I am just pretty darn sure if the Idle mix has never been screwed with then most of the time it is not worth playing with it. It would be best guess at best.

 

I always reply after no vacuum leaks found, check the BAC internal seal for leakage. The BAC can give indication that it's operating properly electrically, but if the interrnal seal is leaking you'll get various idle speeds. Worth a shot.

 

Good idea. However, I need to get a job first.

- k -

 

the instructions for adjusting the variable resistor seemed pretty straightforward and the FSM had no mention of needing to use a wideband or any type of oxygen sensor to adjust it. i would probably mark it before adjusting it at all so if anything you could just set it back to it's original setting. the screw only rotates about 2 full revolutions.