Michael Benno

Hey all, it's been a couple of weeks of troubleshooting and testing all the recommendations above and I thought it is time to post an update since I still have a high idle condition, despite all of your excellent suggestions and directions, and one-on-one consultations.

As a refresher, the car will idle high, 850-1150rpm once warmed up. This problem persisted before my ownership. The running hypothesis is that too much air is getting into the system behind the idle plate (more on this later).

I have been using the Sharktuner (ST) to help with the troubleshooting. I have it connected to both LH and EZK and have it set up with stock parameters. According to the ST, everything looks good, except that the system is trying to fully close the ISV to lower the idle but still too much air is getting through causing the idle to be High. The ST shows the ISV % at ~25% which is essentially closed. According to the ST gurus, typlical ISV values should be ~45%, meaning it has room to add/remove air.

How more air is getting into the intake is a complete mystery:

• Outside leaks: I'm pretty sure there are no vacuum leaks to the outside
  • Smoke test: Pass. I have smoke tested the intake a dozen times and even increased the pressure to 5psi. It's completely tight.
  • Pressure test: Pass. I have pressure tested the intake with compressed air and it will hold 5psi for 1min so again, very airtight.
  • Vacuum test: Pass. I used my smoke machine nozzle to look for vacuum leaks on the running engine, particularly around the injectors. No movement in the smoke
  • Intake Vacuum test: Pass. With the car running I am measuring nearly 20 InHg at the front damper which is very good reading. Anything over 18InHG is an air-tight motor.
    
• Internal leaks
  • Throttle plate: It has been properly adjusted and the stop properly set (see post 38) Greg Brown reviewed and approved that I have it as tight as it can be. It is not binding at all.
  • ISV: I tried a new Lowe and the used Bosch (cleaned) unit both bench tested the same and neither had an impact on idle
  • Venturi - verified proper orifice diameter
  • Breather hoses (and tank vent) - verified proper 1993+ configuration with proper orifice diameter
  • Tested for bypass leaks by eliminating Venturi, Booster, CC vents, and tank vent, and all accessories. No change in idle
  • Fuel Injectors: I tried the OEM injectors and a set of new 4-hole bosch injectors, both sets with new seals (OEM and aftermarket), no impact.
    
• LH Swaps: I tried a spare LH and that did not have an impact

So what the heck else could it be?

Kevin in Atlanta

Use your smoke machine at each injector to see if air is getting past the injector o-rings.

I don't think that would affect idle, but it would be another test.

worf928

Bold, italic…I missed this the first time…

So, what does it do from stone-cold start and how long does it take to begin the high idle? You specify quite a range. Does it fluctuate? Or does it ‘pick’ a random steady idle?

Michael Benno

Hi Kevin! Nice. to hear from you. Yes, this is exactly what I have done, several times. I made sure I tried cold and hot. Still no suction of smoke into the O-rings. I tried this test with both the original injectors and the aftermarket injectors.

Kevin in Atlanta

Next...

Running out of ideas.

This is a Japanese market car, right?

What about the coding plug?

Michael Benno

When I converted the car to a 5spd, I used a USA Manual Trans Coding plug.

Michael Benno

It starts pretty normally, initially at 1050rpm and slowly settles down as the temp increases. I mentioned when warm to indicate closed loop mode when the LH idle fuel map is not overly rich and idle may be adjusted as a result.

Kevin in Atlanta

I've run out of ideas.

jschiller

Just spitballing here since I have no solid advice to offer but maybe judicious use of starter fluid sprayed as near as possible to any air leak sources you can get to. Maybe even a perfume atomizer to minimize the fire hazard?

Jerry Feather

Michael, send me an email: jfeather@bresnan.net. I have an idea that might help. but I will not post it here.

PorKen

An unlit propane torch is good for this.

worf928

Is you description consistent with “idles as it should until the 02-control loop kicks in… and then the idle goes high?”

Michael Benno

here is a boring video but you can see the idle starting at about 1050 and settling to 850-950 as closed loop comes in

gazfish

Maybe it was the mike but sounded a bit weird to me when you cranked it, like a cylinder or two were down on compression?
Does disconnecting one injector at a time show any difference between the cylinders at idle?

SwayBar

I didn't notice in your last list, but have you swapped the MAF for a known good one?

Something else you can try if you haven't already:

Block-off all vacuum lines right where they come out of the intake. So for example, the big vacuum-tree down by the MAF, disconnect the tree and plug the now-exposed vacuum line which leads to the intake. Do this for any other vacuum lines attached to the intake.

This will tell you whether or not you have a vacuum leak at one of the fuel diaphragms, or maybe a leak somewhere under the dash which leads to the HVAC, etc.

Seal them all off and check your idle speed.

Let's say the idle is back to normal, now you can one-by-one reconnect the vacuum lines to see which one/system is causing the high idle and troubleshoot from there.