Hi All,


I have a 97 xk8 convertible 4L.


In the fraction of a second before the car comes to a complete stop, the RPM drops just below 500 and almost wants to stall. The engine immediately recovers and continues at what seems to be a normal idle (about 750ish).


This issue only happens when the engine gets up to normal operating temperature; never happens when engine is cold.


I get similar low RPM when I go from park to drive... or park to reverse... or neutral to drive.. or neutral to reverse.


interestingly, if I shift to 2nd gear before I stop, the RPM does not go below 500 and the car seems to run normally. But if I'm in 3rd or 4th and come to a stop the RPM drops below 500 and wants to stall.


I cleaned the TB and the MAFS but the trouble persists.


Any thoughts on what would be causing this issue?


I found this very issue I'm having documented on youtube but found no solutions.




Thanks in advance.

 

Remove the coil packs, inspect the coil tips and tube for oil and get back with us,

 

That YouTube video is mine...tied to a thread found on this forum. You can find that thread HERE.

I was having those problems last fall, just before my car went into the shop for paint, body modifications and floorpan rust repair. I didn't have time to resolve the stalling issue before the car went into the shop.

After 8 months in the shop, I finally have the car back, although without a windshield so I still can't drive it. All that to say that it will be another month or so before I'm really on the road again to see if the issue remains and what can be done about it.

Read through my thread from last fall to possibly rule out a thing or two on your car. The consensus on the most likely suspect is the throttle position sensor.

Good luck, please report any findings you have.


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Sorry for the delay in responding.
I ended up doing some service to the car. Unfortunatly, problem as I described above still persists.

I installed new spakrplugs as I was experiencing lower gas milage and this actually fixed that issue soIm happy about that.

The coils seem to look and function okay; thay are clean.
No unusual oil in the sparkplug/coilpack area.

I cleaned the MAF a few times to be sure. no error codes are poping regarding that.

Had to repair the front right speed sensor cable because it was cut. Cleaned all the speed sensors. No ABS/Traction control errors coming up.

Cleaned in the Throttle body without removing it. It was pretty dirty and now that its clean the car has alot more pep.. also cleaned the Idle Air Control Valve ( the little hole on the side wall of the throttle body)... but the low RPM issue persits.

I even cleaned the (idle air breather/vacuum hose?)-- that little hose that connests to the front left of the engine ... kinda in the area of the dip stick... the recomended way to clean is with a dril bit...anyways, mine was clean already and I didnt do anyting with it..

So im left with the issue I described at the beginning of the thread.. although the car does run much better.

Puzzled why the issue only happens when the car gets to operating temp.

Could it be a Throttle body issue? position sensor? why would car operate normally until it reaches operating temp? a contact not making a propper contact when hot?

Problem is very consistant...

Any insights appreciated.

Thanks in advance.

 

There are 4 common causes for this.

1.Blow a cigar through a major intake manifold hose, see where the smoke comes from, there is your intake leak.

2.Another common issue is the throttle cable has slack , creating a low tps position reading, simply undo the nylon strap,adjust the square plastic tab by turning it, replace with a new nylon strap when you are happy with the idle.

3.Fuel pump going out and bad fuel filter. when warm.Simply measure pressure when cold, drive around, then measure when hot.


4.If the AC IS ON, a partially seized ac compressor will do the same.

These 4 condition will not set off any codes.

 

Hi All,


1. Had a actual smoke test done and there are no leaks.


2. throttle cable is correctly tensioned (no slack). car responds in time with gas peddle movement.


3.. haven't tested fuel filter and such, but the car does not seem starved for fuel or having any issues when the car actually gets to idle...

4. no issue with AC compressor I can see. car runs the same with or without AC on.






Something is happening when the car transitions into idle... or OUT of idle via changing from idle to Drive or idle to Reverse...
Its like it having a issue when the engine engages a new load ??
The low RPM can be reproduced when the car is at a stop and then I put the car in Drive ... or in Reverse... Parking is so much fun...


Car idles fine (after it momentarily goes thru the low RPM issue) and no issues I can detect when accelerating from a stop.


Which is making me think TPS (throttle position sensor) or IACV (Idle Air Control Valve)?? could something in the throttle body cause this sort of trouble ?


Thanks.

 

This sounds precisely like the issue I was having last fall before my car went into the paint and body shop - see post 3 below.

After getting the car back a few weeks ago, the idle has gotten much worse and now pulsates quite rapidly when the engine is trying to set its own speed...runs fine when I have my foot on the gas and I'm setting the speed.

I really feel the throttle position sensor is at fault.

A remanufactured throttle body - direct from Jaguar with a new TPS - arrived today and I'll install it over the weekend. I'm hoping - and expecting - that my problem will be solved.



.

 

I had same problem, my problem turned out to be corrosion on the main power cables at the grounding point.

The problem identifying the corrosion, was that the corrosion was mostly inside the rubber insulating jacket.

I cut off about 1 ½" of wire and reconnected and viola the voltage stopped going down when the RPM's went down. I did this at about 9 different grounding connections.

When the cable heats up it loses it's ability to carry voltage. That's why no voltage fluctuation problem when the car just starts up in the morning and is cool!

Check your voltage at the gounding points there are many, my worst one was in the trunk by the main high voltage fuse.
Does the voltage go down with A/C turned on and back up when turned off? Check with the lights on a off as well any current draw will reduce the voltage.

If it does I would say there is a problem with cables, at least it is a point to check. There are many reasons the voltage could be reduced, but heat is a big problem.
Google the "Ohms Law"

Do you get any codes or dash light messages when voltage goes down?

Other potenial problems- the battery itself, the alternator, all grounding points under the hood , in the trunk area and in dash area.
Hope this helps and remember

Happy Motoring...

 

The Coupe, please let us know if the remanufactured throttle body fixes your issue.


Vettegood, is there a dumb-down version of how to check the voltage on the connection points? maybe a schematic or something showing where the connections are?


When I'm going very slowly (say parking) and I turn the wheel to the maximum left or right, I seem to be putting a extra load on the system and need more power. Is this normal? I can almost get the rpm to reduce when I do this.

 

When you turn the wheel to full lock it does put load on the engine as its driving the powersteering pump but it shouldnt feel like its going to stall. My car idles about 680rpm

 

Alright, here's the latest on my car. The newer phase of my idle problem - a rapid pulsing in RPM (Post 7 in this thread)- is being caused by a bad VVT on the right bank. When I unplug the right VVT, the idle is perfect. UNTIL...

My original problem...once the engine has come up to operating temperature, a near (or complete) stall when braking to a stop, or shifting into reverse...is still present.

MAF - replaced and ruled out.
THROTTLE BODY - replaced and ruled out.

Here's some language from the Jag Technical Guide for the AJ26 engine and 5HP24 transmission:

Idle Speed Control

During engine idle speed control, the ECM operates in a closed speed control loop to maintain a given target idle speed. The ECM uses gear selection, intake air temperature and battery voltage to determine the required target idle speed.

Gear selection is derived from the input of the Park/Neutral switch in the transmission rotary switch.

Battery voltage is monitored and, if low voltage is detected (11.8 V and below), target idle speeds are increased by up to 50 rpm to increase the output from the generator.

When the ECM selects a change of target idle speed, overshoot is kept to 50 rpm maximum. Certain vehicle services/functions cause a significant change in engine load as they are selected on and off. To minimize the effect on idle speed, the ECM anticipates the change in load rather than correct the subsequent change in rpm. The services/functions the ECM anticipates load changes for are:

• gear shifts between Park/Neutral and Reverse/Drive
• A/C compressor clutch
• headlamps and side lamps
• windshield and backlight heaters
• radiator cooling fans

The ECM detects gear shifts, headlamp status and side lamp status from their related status messages on the CAN data bus. The ECM directly controls the A/C compressor clutch and the radiator cooling fans. The windshield and backlight heaters are controlled by the ACCM upon consent of the ECM via the heater request/load inhibit circuits.

If a fault develops in the idle control function, the ECM goes to open loop control. During open loop control, rpm is within +100 and -0 rpm of the target speed for a warm engine (ie. when the coolant temperature is >30 ˚C (86˚F).

The only "function" that seems to affect the idle speed in my case - and it sounds like your case as well - is the engine load of shifting into gear or braking to a stop.

Still some thinking to do on this one.



.

 

I am going through the exact same issue it has been an off and on problem for months, do you have an update on your issue

 

Remove all coil packs again. Remove all rubber boots off them. Clean the corrosion off all the metal springs using electrical cleaner and a q tip, and wire brush if needed.

Clean the inside of the boots with the cleaner. Let all dry. Go for a test drive.

2.Check the vacuum line from the tb to brake booster for cracks.
3.Replace the engine crankshaft sensor and coolant temperature sensor. (The crank sensor, its ok to cut and splice), the connector is impossible to get to.
4.Clean the carbon out of the driver part breather orifice valve cover outlet hole with a small drill bit .

Its usually all of these problems. Don't ever forget, a shop with a GOOD SCANNER, can run live diagnosis, while its being driven. A trip to the dealer for this will cost a little over $100+ to see whats failing if you cant figure it out.
BEEN HERE DONE THIS. MINE WAS THE COIL SPRING CORROSION (THE TIPS THAT HOLD THE SPRINGS MAY EVEN BE SHOT,),THE DRIVER VALVE COVER PART LOAD ORIFICE CLOGGED AND THE CRANK SENSOR(HARD STARTS) OR A COIL FRIED INTERNALLY DUE TO PREVIOUS COOLANT LEAK FIXED