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The issue is my idling speed. It’s very erratic, but only sometimes – for example, going along recently, I could feel that there was no engine braking when lifting off the accelerator pedal – I slipped the gearbox into neutral and the revs were “stuck" at c.1500 rpm – video attached, sometimes it goes up to 2,000rpm! By the way, it never stalls or goes below 800rpm....
based on best guess you have a 90 correct?
Your TPS has failed to send a signal to the computer
It could be filled with oil
when was the last intake refresh done?
The logical first consideration is the idle stabilizer. It could be sticking occasionally. It's buried under the intake. There is a shade tree fix that can clean out gunk and perhaps free the sticking bypass door. Worth a try. On the driver side of the intake manifold is a ~3/4 diameter hose that goes from the side of the manifold back down under the rear of the fuel rail. The rear end goes to a fitting that feeds the stabilizer. There is a junction in the middle of the hose that has an arm that goes to the brake booster. Unfasten the rear section of the hose and squirt 15-20 seconds of aerosol WD-40 down it. Start (or at least try to) the motor and run it briefly to suck the WD further into the stabilizer. repeat the WD-40 squirt. Refasten the hose. Run the engine some more varying the throttle idle and off idle.. See if that helps.
Also, I would verify that the throttle switch is adjusted properly to engage the idle switch position. In a quiet garage, open the hood and move the throttle cable arm on the throttle quadrant SLIGHLY off idle and back. Note the cable should have a slight amount of slack when seated. If not, make an adjustment to the throttle cable to create a slight amount of slack. Then turn the arm until you can feel all the slack is gone and then turn it slightly more. Within a few degrees after slack is removed you should hear a faint click from the throttle switch located underneath the passenger side of the intake manifold. Then allow the throttle arm to return . As it seats, you should hear that click again. If not, the idle switch is not tripping properly. It could be broken or it could require adjustment at the switch. Hearing the click consistently a few degrees of rotation after cable slack is removed verifies proper adjustment. Sometimes the idle switch tripping is inconsistent if the throttle cable and throttle mechanism are corroded. Some WD-40 or light machine oil (3 in 1) on the pivots and cable might help. Certainly the throttle switch could be broken or filled with oil as Stan said. See if the above helps before you tear into the manifold. The switch can "break" electrically and still click, but this should cause a more consistent inconsistency in idle. The electrical action of the switch can be tested either by a diagnostic tester (Theos Diagnostic or Hammer or others) or by simple continuity measurements at the EZK plug as described in the Workshop Manual.
Perhaps there was a more specific clue in your video but I didn't get much from it.
The ISV is designed such that if it fails to operate the net balance of air flowing through the venturi and the detente poition of the ISV approximates the air needed to hold a stable idle at the same rpms [675] of a motor operating correctly at temperature with the a/c switched off. Thus what your video suggests assuming the a/c is not operating is that for whatever reason the ISV is not operating. The throttle position switch issue has been covered already, the cable connector under the throttle body may be disengaged for whatever reason or the ISV itself is shot/stuck. My original ISV was sticking some 18 years ago and when I pulled it, I found the port all gunged up with a dry grey powdery substance- cleaned it out and it continued working until I changed it out for a new one a couple of years ago- still OK probably.
I am not a big fan of the WD40 shoot out method but if it works why not- nothing to lose as it were.
In case it is not clear to you, the throttle position switch can be corrupted and it is quite common for the full throttle switch to fail, the idle switch less so but fail it can. The idle system does not kick in until the TPS signal tells the brains that it is "time to idle". If that logic signal is not realised the ISV does nothing and the thing defaults to the power off position that supports an idle of sorts as mentioned above. Another little test you cn do is when warm and operating, switch the a/c on report what happens- it should pull the revs down and maybe cause the motor to stall.
In my post I just called it the throttle switch. TPS = throttle position switch = throttle switch. It has 3 states: Idle, Cruise, Wide Open Throttle. Idle is controlled by a microswitch that you should hear click on/off, as I described. This is rather important to a stable idle. Wide open throttle is a ramp at the other end that pushes two contacts together (no click). That more often fails, often just due to too much slack in the throttle cable so the switch doesn't quite reach enough of the ramp to close the contacts. This doesn't lead to any obvious driving anomalies. It impairs enrichment of the fuel mixture and slight ignition timing retardation that should occur when you push the gas pedal beyond about 3/4ths of the way to the floor.
In your case, it would be good to at least verify that the TPS clicks as it approaches and leaves the idle position. That's easy to do. As I mentioned, that doesn't completely guarantee it is actually sending the signal to the fuel injection and ignition brains, but I would look elsewhere (the idle stabilizer = ISV = Idle Stabilizer Valve) if the TPS idle click is present. We could go into a lot more detail here, but if you want to try to understand and fix this yourself, you should get a copy of the Workshop Manuals (WSM), available on CD from 928sRUs.
The Work Shop Manual (WSM) that Roger sells on CD ROM is awesome.
But if you want a reasonably complete copy right now, there's a download available. There's a link for it in the New Visitor sticky.
There's also a list of all the common 'shorthands', abbreviations and acronyms, too.
I popped up to Paul Anderson and he checked the TPS with the Bosch Hammer - all OK.
One of his techs Rich noticed that the fuel injection wasn't cutting out at lift off and approaching idle (I'm trying to quote what he said - forgive me if I have the wrong terms).
Paul swapped out the LH ECU for one of John Speake's repaired units and hey presto - all good. The driving experience had been transformed with quicker cold start and a very steady idle both cold and warm.
Had an x-pipe fitted as an early Christmas present to.....me! Lovely noise & more power....
I popped up to Paul Anderson and he checked the TPS with the Bosch Hammer - all OK.
One of his techs Rich noticed that the fuel injection wasn't cutting out at lift off and approaching idle (I'm trying to quote what he said - forgive me if I have the wrong terms).
Paul swapped out the LH ECU for one of John Speake's repaired units and hey presto - all good. The driving experience had been transformed with quicker cold start and a very steady idle both cold and warm.
Had an x-pipe fitted as an early Christmas present to.....me! Lovely noise & more power....
Cheers
John
We tend to assume that all problems stem from the LH but I dare say somewhere along the line a few EZK units have failed. Any original LH unit is on borrowed time so best to have JDS refurbed unit or do as I do and have a spare unit to hand for when it goes south.
I like the X-pipe- I have one of Louie's original units- yours has a much more exaggerated "X " than mine- any idea where it came from/was made?
11-30-2019 | 03:46 PM
Erratic idle speed
