My '95 does have an air bypass screw used to set the idle. From what I have learned on the forum, I really shouldn't have one.

I was asking because I increased the idle speed on my '95 trying to solve my 32 second stumble. It helped. After the ECM learned the new components, I had to close the air bypass screw to reduce the idle back to specs and solve the lean condition that I created by opening up the screw.

Your default air passage is determined by the 3mm screw that adjusts how close the throttle plate is to fully seated/closed. Someone on this forum had told me that the throttle plate should be adjusted to have a .05mm clearance between the point perpendicular to its shaft and the bore wall.

It might be worth a look to make sure it is to spec. With the ECM relearning to manage the engine with new components it cannot choose a workable fuel map unless all components are within workable ranges/thresholds.

Good luck. I am still working with my '95 fine tuning the idle and diagnosing a random miss after replacing most of the components/sensors.

 

Vee,


I told you wrong earlier. The throttle plate clearance should be .05mm. Not 5mm. Sorry.

 

I am not saying this is a fact, but I think you can rule out the TPS. The failure mode on those is bad shifting, or the intermittent shut-down at speed.

You could have a bad ground. I had a bad ground in mine once but the symptoms where different. But a "stuttering" ground to the coils or MAF could be causing the problem.

You are going to have to systematically eliminate parts and their related wiring.

 

OK, I guess I can start at the coils and see which one is not like the others...every 32 seconds.

Then I can check the IACV. Not sure what values I'll be looking for, but I'm sure a forum or internet search can turn up the correct value...or the service manual!

I want to thank you guys for sticking with me with this. I value your help greatly.

 

I haven't reset anything. I think I'll try the negative cable to the positive wire thing, but I don't think that works on the AJ16.

When I took it to the Jag Specialist, he did say that they checked the clearances at the throttle plate.

 

Something to remember: My 32 second stumble began to reduce in severity after I replaced the MAF. It did not immediately resolve itself when the MAF replaced.

It took driving the car repeatedly to give the Ecm time to do its thing. The idle improved each time that it was driven.

Now, about 2 months later the idle is smooth and at 600 rpm ish. Since I could not manually reset the adaptations, I had to wait and hope that the ECM would figure it out. I suggest that you disconnect your battery for a few minutes and then reconnect to force the ECM to use its default maps and relearn the components and how to manage the systems. Make sure you know your radio code before you disconnect the battery.

Then be patient and drive it to see if it will improve. I have my fingers crossed for you!

 

My '96 doesn't have that screw either, Cyberg.
RagJag

 

I haven't done this yet. I will try it now.

Thanks.

 

I was not able to remove the battery terminals last night, you need a small open ended wrench, I don't see any other way to do it.

Anyways, there was a lot of traffic last night, so I decided to drive with the IACV unplugged. I turned the car on, not engine, unplugged the IACV and then started the car. Beautiful! No dipping, no problems. I thought I was a genius.

While on the beltway, engine now fully warmed up, I feel more of the engine surge I was talking about when coming to a stop, so I shift into neutral. I drive then when I know braking is imminent, I shifted to neutral to see what would happen.

The tachometer starting going up! It wanted to go to 1,500, maybe even 2,000. Slowly and gradually, as if I was feathering the gas pedal. Then it would come down and then go up. Not violently, or sporadically. It would float up to 1,500 then make its way down to 900, then casually float up to 2,000, then back down again.

I have an old TPS that I believe, but cannot trust is good. I will try that.

I will also use some gasket dressing to mate the throttle body with the engine. Always seemed strange that it was a metal to metal connection.

 

Vee - I'm nearby in Falls Church. Where did you take your car in Springfield? I've replaced just about every part related to the idle (IACV, CPS, throttle body, EGR valve, spark plugs) to no avail and think I need the pros to reprogram my ECU.

 

Any update on this?

 

I replaced the TPS with one I had previously. If it is bad, it wasn't for this problem...unfortunately it did not solve the problem. I checked to make sure it had exactly 0.6v on it at idle.

I stuck needles in each of the connectors at the coil, and they were all fluctuating at about the same range. (DC - 50mV) I don't know how to check what the coil is getting, just what gets to the coil just before the connector.

My voltage is reading at 13.3, until the 32 second hiccup, where it drops momentarily to 12.5v.

O2 Bank 1 Sensor 1 - 0.07
O2 Bank 1 Sensor 2 - 0.09

O2 Bank 2 Sensor 1 - 0.11
O2 Bank 2 Sensor 2 - 0.10

I did get the Timing Advance value to blip, not consistently. It locks on to 10 degrees relative to #1 Cylinder. Sometimes, it would move to 12 and 7 at the 32 second mark. Sometimes it would just blip slightly, other times it wouldn't blip at all. I think its such a momentary blip, the reader would have to catch it dead on?

Any advice?

 

Sorry, but I do not have a 'Silver Bullet' solution for you. If you still have your IAC valve disconnected, I recommend that you reconnect it, disconnect your battery for a few minutes, reconnect and then drive your XJS.


Initially, you will still have the 32 second stumble, but as the ECM relearns the system and if all the sensors are within ECM programmed feedback boundaries, the stumbling will begin to diminish as the car is used. The ECM will figure out which fuel maps to use based on the values received from the sensors. If one or more sensors are still out of wack, the ECM may not be able to lock in on the correct maps and the stumbling may continue.


Drive the XJS and see if the 32 seconds stumble doesn't diminish. Mine did. I am rooting for you.

 

Done. I will continue driving and see what happens.

In the meantime, I will begin assembling a list of expected readings so I can start testing the readings at the ECU. I believe that some process is looking for a value that it's not getting. I think it checks for it every 30 seconds at idle.

I wonder how I can tell of the car is operating in open or closed loop.

I'd like to compare reading sensors are sending, versus what the ECU is seeing at the harness. I wonder if there's a short somewhere that delivers a partial or diminished signal somewhere.

Thanks for your help and I will update this thread as any more information becomes available.

If anyone has any data for expected ranges of values at ECU pins, I would appreciate the help.

 

Oh, I also discovered that the Evaporative Drive Cycle is still showing as not completed. All other tests are complete.

 

I also cleared all stored codes...which were many, but all indicative of all the plugging and unplugging of sensors I monkeyed with. (I'll check back to see if any codes pop up). It's strange that I had 10 codes stored that my standard OBD2 reader didn't pull.

I reset my TPS too.

No change in my idle.

 

Could this be a dying alternator?

I was just driving and I noticed when I put the fan on, the voltage dropped. I pressed the AC button on, but no discernible difference (on heat?).

Then I started turning accessories on, seat heater, interior lights, and with every button/switch activated, a noted drop on the voltmeter!

When I activated the hazard lights, the needle fluctuated in rhythm of the lights! When I turned the high beam on, I swung the needle to the left of 13! I almost stalled this thing out.

Bad alternator or bad ground?

 

It would be worth your time to clean the ground connections before replacing the alternator. Don't overlook those to the right of the battery.

 

Checked the voltage drop from the negative post on the battery to the bolted down connection, just to the right of the battery. 6.1mv drop. I wasn't expecting that much.

Drove in today. Checked the car's battery with a multimeter. It was 12.10 before startup.

After starting the car and letting it run for a little while, the battery read 14.3 using the multimeter.

When I got in the car, I was only reading 13.3 from the OBD2 reader. As I drove, I never exceeded 13.3, however as I turned on acccessories, I was able to drive the voltage reading from the OBD2 down to 12.5 which would come back up after I exceeded about 2,000rpms on the highway.

When I made it to work, the car was reading at 13.0 with a seemingly slow steady drop (started at 13.3 off the highway and when I eventually turned the car off, it was at 12.9) I didn't have too much time to watch the voltage drop more.

The funny thing here is that the battery, using the multimeter and the engine still running was at 14.10! (The OBD2 reader was down to 12.9)

I waited for the 32 second drop, and the battery went down to about 13.5 using the multimeter. I didn't witness the drop at the OBD2.

Where is the OBD2 taking it's battery readings from? Is it normal to expect such a difference at the battery and at the OBD2 port?

 

My guess is that the OBDII reported voltage is what the Ecm is seeing. My '95 has a black ground wire that is a part of the Ecm wire loom. The wire has a metal loop that bolts to a stud on the Inside passenger side of the firewall.

It would be beneficial to make sure that the ECM ground connection is bright and shiny and actually connected.