I posted several months ago about a rough idle problem that I've had with my 93 XJS and how several repair shops have not been able to find the problem (but have charged me almost a total of $1000). Well, I found a shop that has great reviews and comes highly recommended.
After several days of diagnosing the car, they decided to perform a smoke test. They discovered that the intake gasket needed replacing and the egr gasket needed replacing and several vacuum hoses needed the same.
Several weeks of waiting on parts and $1200 later. It still idles rough and runs rich and they still can't correct or figure out.. what is causing it.
So far, I've taken it to 4 so called foreign car specialists and spent well over $2000 and still have the same problem I had a year ago. (rough idle and rich running) I've replaced just about every emissions, intake device and fuel enrichment part that the car has and have followed many suggestions about fixing it.
After a lengthy discussion with the shop, we decided that I will add some fuel cleaner and take it on the road for a long trip and hopefully clean the injectors and valves or replace the injectors. In actuality, they have no idea of what to do at this time. We both are just guessing and grasping at straws for an answer. Any more suggestions, maybe someone out there might have a solution. I am going to try and drive the hell out of it today and see if it makes any difference.

 

You should really try to take your car to a shop that has the PDU. They can hook it up and reset parameters and whatever else that thing can do to the ECU.

There's one shop that has it here in the Washington DC area, and another in Minneapolis, Minnesota.

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Minneapolis shouldn't be too far from you. (What 7 hours?)

 

93 greenconvertible, I also had the idle problem and fixed it by installing a new crankshaft position sensor (crank angle sensor). I also drilled a 3/32 diameter hole in the throttle butterfly because I could smell the idle mixture was rich. My engine idles perfectly now at the correct 600 rpm. Your engine may be different as it is a '93 while mine is a '96. I believe the sensor is what did the trick. New plugs and coils nor a new stepper motor helped. I had about given up. I believe I posted this earlier but thought it may help.
Cheers, RagJag

 

ragjag, that's very interesting, this is the first time I ever heard of that. Did you do both the sensor and the hole at the same time or did you do one drive it and then do the other. I can understand how the hole in the throttle plate would help, but I'm don't understand the crank angle sensor, but I might try both at this point. Thanks for the suggestions.

 

Could you give a little more detail about the rough idle?
Does it happen on a cold start?
Does it go away or get worse when the engine gets warm?
Is the idle hunting up and down? Is it idling high or low?
Is the engine misfiring?
What makes you believe it is running rich? Emissions? Smell fuel? Poor mpg?

 

How about having the injectors professionally cleaned? By that I mean removed from the car and sent to a specialist.

Whenever I've had it done I've always experieneced a smoother idle

But, as mentioned above, more details might be helpful. How rough is "rough"? An outright misfire type of roughness? Or more like an annoying tremble? The former is sometimes eaier to solve than that latter

Cheers
DD

 

The rough idle I am describing is first worst when started up cold, at that time, it searches for a smooth idle. It does get better as the engine warms up, but never really smooths out. Slight missing sound from the exhaust, but mostly, just stumbling when idling. Also, the injector cleaning was one of the solutions that the mechanic and I talked about and if I can't get it to smooth out, that will be on the list to thing to do.

 

Have you tried replacing the oxygen sensor yet? If the O2 sensor misreports a false lean condition it forces the ECU to add more fuel when not needed.

I recently reported here an idle problem on my '94 not too long ago and which was totally resolved with a new O2 sensor. This is something you can do yourself and the cost is about $75.00. The P/N on my '94 AJ6 is 13313. I doubt that the '93 AJ6 would be different.

Cheers and good luck,

 

That P/N 13313 was a Bosch "Premium Oxygen sensor"

 

As Doug alluded to, sometimes these idle issues can be elusive

If you haven't already done so, down load the AJ6 Engine Management S91 publication, it gives you an in depth explanation of how the system works, including 8 pages on the idle strategy employed. Not knowing exactly what you have tried, here are some easy checks to consider.

O2 sensors can degrade over time and get sluggish but you mentioned that you had replaced almost every fuel, intake and emissions part? Also the O2 sensors are not a factor on cold start as the ECM ignores their output until the engine gets above 95F. You can back probe the sensor connector in the engine bay and look to see that the voltage is switching quickly, it should change between about 200mv and 800mv every 2-3 seconds. If it changes slowly then replace the sensor.

If you changed the idle control stepper motor, did you reset the base idle? You can do this manually, there is a procedure in the service manual, basically it involves turning the ignition on and off and disconnecting/reconnecting the stepper motor in a prescribed way. Easy to do and will eliminate one variable.

Have you cleaned the idle control valve body or the throttle body? They can get gummed up. Again easy to do. Also check to make sure the throttle disc gap is set correctly at .002" Also the EGR valve as it can get gummed up and not close completely.

MY93 cars suffered from a poor connection at the MAFS. For MY94 and later, Jag used a gold plated connector to alleviate the problem. Have you checked your connector? Many people replace the sensor but most often it is the connector that causes the glitch. Inspect and clean as necessary and make sure it is seated correctly.

Have you measured the output of the TPS? You can back probe the connector and with the ignition on (but engine off), rotate the accelerator quadrant slowly from idle to WOT. You are looking for a smooth change in voltage from about 0.6v at idle to around 4.8v at WOT. If there are any dead spots, the wiper on the TPS is probably worn so the TPS will need to be replaced.

Also, have you checked the purge valve and make sure it is holding vacuum?

I'm guessing you have checked the dizzy, rotor, plug wires and plugs? Have you also checked the ignition coil itself? Measure the primary and secondary resistance of the coil. I had a faulty coil recently that created rough running conditions. It is simple and fairly inexpensive to change.

Electrically you will want to check the grounds on the engine bay bulkhead, make sue they are clean and tight. Also check the battery voltage at the battery and also at the terminals in the engine bay. The ECM uses the measured battery voltage as a final trim to the injector on time so it can cause idle problems if it is noisy.

The good thing is that all of these items can be checked easily without throwing parts at the problem which often mask/confuse the issue.

 

93 Green conv., I installed the crank sensor last. The car has not missed since I did that. That sensor is not too expensive so I would try that before other more expensive options.
RagJag

 

I guess I'm just getting frustrated with this issue. It's been a year and I've tried every suggestion and paid out over $2000 to mechanics to try and solve this problem to no avail. I love the looks and feel of the car, but I think I'm just going to sell it. I can not afford to keep throwing money into it when no mechanic or shop in the local Chicago area can fix it. They all say they can and then say "Sorry, that will be $700". Not one mechanic has told me that they won't charge me if they can't fix it. The O2 sensors and another idle control valve motor are the last 2 repairs I'm going to try and if that doesn't correct it, Who knows.

 

I know it can be frustrating ;(

Please note though that I did not suggest replacing any more parts. Throwing parts at a problem like this almost NEVER works. Rather it is necessary to check, inspect, measure etc the various sensors and wiring/connectors to help pinpoint the problem. Unless you have a really good mechanic to go to, many will just do basic troubleshooting and quickly suggest changing parts. Not a good recipe for success.

To highlight this, I have just gone through something similar. I recently purchased a 95 XJ6 from another forum member. He had been chasing a bad idle/misfire problem for over 18 months. Like you he had changed virtually every part that might have a bearing on the problem, all to no avail. One of the first things I did was hook up a scanner and the crazy fuel trims told me that the problem could be very simple. It was!! The O2 sensors were switched over so the ECM couldn't make up its mind how to fuel, hence misfire. It took just a few minutes to fix and cost zero. If you take a methodical approach to the problem, I'm confident you will be able to solve it, perhaps at little to no cost!!

 

Thanks for the positive advise. I am going to change out the O2 sensor anyways and I just ordered a new ICV motor, cause I did throw a ICV code, once. I will probably keep trying, but the cost is taking the fun out of the car. Maybe I'll just take a break from working on it till after the Holidays. Thanks

 

93greenconvertible, Did you ever replace the crankshaft sensor?
RagJag

 

No, not yet, I'm trying several other things that have been suggested, but if the others don't resolve the problem the crank shaft sensor is on the list.

 

Yes, you're right about the 95F, yet, how do I explain my car's behavior.
Loss of acceleration when warmed up and also erratic idle with creeping up a/f ratio (have wideband gauge). For the idle issue, I checked for possible vacuum leaks (propane) but no leaks found.

From several tips on rough idle articles read, I replaced the O2 sensor (pita), but that was it. It felt so nice to have a smooth idle again and normal A/F ratio readings on my wideband, at around 14.7:1. Before the fix it would tend to creep up (lean) and peg at the top limit (lean-est?), sometimes if would even die if left to idle for a while (had to touch the gas pedal at the red light).

Theoretically I cannot explain the below 95F, but it clearly fixed the cold and hot idle problem and, as per 93green, his problem does not necessarily disappear when the engine warms up. Maybe it'll work for him, as well.

Cheers,

 

Reinaldo,

I'm glad you found and fixed your problem. It could be the OP's problem perhaps, though it seems he may have already changed them? However, in your case, you rather proved my point in that you first measured AFR, inspected for air leaks etc and THEN changed sensors based on what you knew.

That is all I'm suggesting to the OP. If you read through the archives you will find literally hundreds of posts which follow a similar theme of "Help! my car has a terrible idle/is rough/stalls etc etc. The good people on this forum will give advice as to what it might be and often the owner goes out and buys a part(s) and starting changing them. Often this is unsuccessful and the owner gets frustrated and spends a TON of money. Just in this thread alone there are a number of suggestions to replace certain parts and if you read the OP's previous post you will see a lot more. It's easy to understand why he would be frustrated.

The problem with a statement like "my car idles rough" is that there is not enough data to diagnose the problem. We can make guesses based on our own experiences/knowledge etc but they are only guesses.

So the owner may well get responses of "it could be a bad………
MAF
Coil(s)
plugs
dizzy
fuel pressure
dirty fuel
O2 sensor
CTS
CPS
ECM
IACV
EGR
Wiring
Grounds……. etc, etc.

Now all those guesses have merit but if the owner was to just go and start replacing all these parts, it would be (a) very expensive and (b) often may not solve the problem.

In my case with the new XJ6 I bought, the car came with an astonishing array of spares that the owner had bought to solve his issue. I'm not kidding, literally thousands of dollars worth and often multiples of the same item (like 3 CPS's!!) In the end, just taking simple measurements would have pointed to the problem and the solution which cost ZERO.

All I'm suggesting is "measure twice, cut once"

 

93greenconvertible, I hope the crank sensor is not too far down the list. It is not as expensive as the TPS or the MAF. The only thing I don't know is if your 1993 engine has the same fuel injection system as my 1996. I will admit to being amazed that after installing the CPS, the engine ran smoothly cold and hot. No miss, slowing rpm or stalling after that.
Cheers, RagJag

 

Ragjag, while I'm waiting for my other parts to arrive, I decided to find and remove the crank sensor, as the case would be, the 93 has 2 different styles of sensors, depending on your engine number. Anyways, I removed it and it was totally covered with old grease. At one time the previous owner must have had a large oil leak and it covered the sensor. I cleaned it as well as ordered a new one (after making sure of the correct one). I then decided to replace the clean old one and see if it makes any difference. I did a hard reset of the computer and started it up and actually seemed to run a little smoother, not totally smooth and it still stumbles at idle, but I only let it run for about 5 min.. When I get the time, I'm going to drive it around to see if the computer needs to adjusted to the new readings.
I still have several new parts coming including a new sensor, but maybe I'm getting closer to a smooth running car. If this is the solution, I'm still rather pissed that 3 so called quality repair shops never checked this sensor as well as the O2 sensor. I paid big money for nothing, I've done more fixing of this car then the Jag mechanics.