intermittent problem 92 3.9

Next instalment.

Finally got to the bottom of the manifold air leaks and reduced the idle back to normal. Car serviced, pink slipped and rego'd and running like a dream for 2 days until yesterday. I had another stall and this time the car did not start up again as it has done previously. It goes through a cycle of revs dropping to near stall, followed by revving to 1200, then dropping to stall, then revving etc.

I nursed it home tonight by left foot braking whilst putting it in neutral and holding the revs up over 1000rpm when I came to junctions and lights. I will check the codes in the morning and try a different MAF. TPS wiring looks ok but I will double check this. I have a spare new coolant temp sensor and will try this next. I will keep you posted on progress but would appreciate your thoughts.

Ah... Left Foot Braking, brings back memories of Sarah having issues with the Idle stepper-motor .:mad:

Yes, she'd stall on a trailing throttle, the busier the intersection/roundabout the more likely she'd die as you eased up on the accelerator, the clue being suddenly heavy steering... Music is invariably loud enough to drown out the final choking noise.

- I became adept at changing into neutral, re-starting, revving a bit and dropping back into D, all the while controlling the final few metres with the left foot...

IF you replace it, and you go for economical-aftermarket, be gentle when you tighten it up, better to use a thread-locker than brute force. - Don't ask how I know.:angel:

By the sound of it, your problem is more likely to be around the Plasma Tubes or the regulating trans-dimensional nanobots...:eek:

james in Gosnells,
The Lady Sarah, '95 Classic Vogue SE with working air suspension.
- Just don't mention the Leaking Sun Roof.:(

Quick question if I may.

The 14CUX troubleshooting manual states that the 40 way multi plug connecting to the ECU has 4 pin numbers moulded onto the rear of the plug designating positions 1, 13, 28, 40 in the 4 corners.

1-13 run from right to left across the top of the plug. 28-40 right to left across the bottom. However it also states that pin 14 sits UNDER pin 13 suggesting that the numbering of the middle row 14-27 is left to right, i.e. the reverse order.

Could someone confirm if I am reading this correctly please. Cheers.

Quote:

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Originally Posted by superquag

IF you replace it, and you go for economical-aftermarket, be gentle when you tighten it up, better to use a thread-locker than brute force. - Don't ask how I know.:angel:

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Thanks James. I tried another stepper motor from a known working vehicle and the results are exactly the same :( I also swapped out a known good MAF and again, no change.

HI Philip, I took the TPS out and unwrapped the cabling from end to end and examined it carefully. I did not remove the heat-shrink but felt carefully through the joints and all appeared good. There was a nick in the red cable exposing copper but no real damage to the cable itself. It is unlikely that this part of the cable could have earthed anywhere as it floats freely away from the rocker cover at this point.

One thing that gives me comfort is that after clearing the Code 19 - Throttle potentiometer input low/airflow meter high, when refitting the TPS I spun it through 10 degrees so that it was in an off-idle and on starting the car I saw a Code 17 - TPS fault. As a result of this the idle revs were up to around 1000 rpm plus and consequently there was no stalling (or near stalling) with the previous rev fluctuations. Moving the TPS back to its normal position showed the fault code cleared once I had reset the ECU with a return to the fluctuating idle. The error code would have been due to the voltage being outside the range .085 to .545v I presume as a result of being in an off-idle position (maybe I am mistaken here?).

If not that leaves me chasing down an air leak, or a bad ECU according to the Electrical Troubleshooting manual. I will take it back to my (good) mechanic tomorrow to check for air leaks.

FYI there is a base/kerb idle adjustment on the throttle body.
It is very difficult to see but if you look at the bracket that holds the kick down cable you will see a hole drilled at the rear.
Immediately above that there is a Allen socket which is very small about 2mm AFAIR.
I had another thought
that the pr,oblem could be the stepper motor. The plug has lost its tangs and may have come out a bit or the stepper is dirty or failing. This could cause stalling if the curb idle is too low and high idle if it opens completely.

Regards Philip A

Thanks Philip but I am steering away from the Stepper Motor. I took the original and the spare, cleaned them both with Circuit Board cleaner including the plugs & sockets, examining the contacts carefully. Exactly the same results for both.

I might take a friends TPS and have the wiring extended to fit for testing. He is fairly laid back with this as long as it works again when he refits otherwise I will need to buy him a new one :)

I am trying to work through in my head what will trigger a fault code 17 in the ECU. I guess the ECU knows from the other inputs (MAF etc) that when I fitted the TPS 10deg anti clockwise (TPS off idle) that the voltage was higher than it should be in relation to MAF input (no input)???

BTW, the stainless T-Piece that would normally connect the vacuum hoses to the plenum is not capped i.e. the now unutilised foot of the T. This has been the case from day 1 (for me) unless something has fallen off?

AFAIR. There should be a hose going to the inlet manifold after the throttle body connected to that t piece
Again AFAIR I used the 14 CUX original hose that went from the vent on the RH rocker into a t piece on one of the hoses from the rh side of the inlet.
I will have a look for an image.
It should operationally be the same as a 14CUX. Ie one hose from vent to throttle body and a restricted hose to vacuum.

Regards Philip A
That is probably why you have fast and unstable idle.

I have deleted all photos of the engine unfortunately but I did find the number sequence for the ECU plug.
You are correct 14 is above 13.
Anyone know how to attach an existing attachment from "attachments" in my control panel to this thread? As my oxy sensor guide is still there.
Regards Philip A

Quote:

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Originally Posted by PhilipA

Anyone know how to attach an existing attachment from "attachments" in my control panel to this thread? As my oxy sensor guide is still there.
Regards Philip A

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Just open your attachment and copy its URL from the address bar into the box you get from clicking the "insert image" button above the posting window.

Hmmm,doesn't seem to work on iPad but if you use the term

Finally the V8 3.9 O2 project

In the Aulro specific Google search engine at the bottom of the page you will find it.

Regards Philip A