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  #1  
Old 06-23-2011, 05:40 PM
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Default xk8 rough idle- gets more rough when i rev and return to idle

EDIT: I Did not want to bump this as it was an old thread, but yes, the driveplate was the issue. My sliding it out technique didn't work, but once all the tranny bolts were off, it was only 10 mins of work to unclip all the tranny harnesses and lines, and move it out of the way completely.

My car is acting up again. I am pretty much stumped as i have no engine codes, and no loss of power. the car only acts up at idle, anything over 1k rpm is perfectly fine, no change in driveability. When i first start the car up, it idles rough and then kind of fixes itself (still rough, but not as rough). However, when i blip the gas to say 2k rpm and take my foot off the gas to return to idle, the idle is much more rough. I checked for vac leaks, disconnected my injectors one by one and they all make a difference in idle, and disconnected my injectors one by one and they all make a difference. Any advice. OH, also, i cleaned my throttle body. my car idles around 600, is this a bit low?

Car is a 99 xk8 vert

Also, when i start up the car in the morning, it takes a few more cranks than usual to get it started. However, if i shut off the car, and restart it, it starts right up. I was thinking this could be the cause of a bad fuel filter, but that wouldn't give me a rough idle like this i don't think

Last edited by xjrwithproblems; 10-23-2011 at 02:35 AM.
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Old 06-27-2011, 01:24 PM
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I just had a bit of rough idle on mine at 130k miles. I bought it several years ago and never changed the spark plugs, so that's what I had done. After that, the idle still seemed a little rough, but I just drove it. After 2 weeks of daily use, it seemed to idle smoother. I am not sure, but maybe the engine computer recalibrated & adjusted after being driven. Does anyone have similar experiences?
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Old 06-27-2011, 01:58 PM
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Quote:
Originally Posted by xjrwithproblems View Post
My car is acting up again. I am pretty much stumped as i have no engine codes, and no loss of power. the car only acts up at idle, anything over 1k rpm is perfectly fine, no change in driveability. When i first start the car up, it idles rough and then kind of fixes itself (still rough, but not as rough). However, when i blip the gas to say 2k rpm and take my foot off the gas to return to idle, the idle is much more rough. I checked for vac leaks, disconnected my injectors one by one and they all make a difference in idle, and disconnected my injectors one by one and they all make a difference. Any advice. OH, also, i cleaned my throttle body. my car idles around 600, is this a bit low?

Car is a 99 xk8 vert

Also, when i start up the car in the morning, it takes a few more cranks than usual to get it started. However, if i shut off the car, and restart it, it starts right up. I was thinking this could be the cause of a bad fuel filter, but that wouldn't give me a rough idle like this i don't think
First, if you cleaned the throttle body, have you disconnected the battery so it can reinitialize the base air. It has to do that since there is now more air getting by the butterfly with the bore cleaned.

The rough idle you describe is another matter. One possibility is a one tooth jump in a secondary timing chain. Another is that a VVT unit may have failed and is stuck in a retarded position. Either one would require pulling the cam covers for a look see.

Good luck!
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Old 06-28-2011, 01:38 PM
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Hey Gchin, thanks for the advice. I checked my plugs and grounded them to check for spark, they all have a nice blue spark so i don't think that could be the problem.

Xjrguy, This was actually what i was first suspecting as I did my tensioners not too long ago. Pulled off the valve covers and the cam flats are perfectly aligned.
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Old 06-28-2011, 02:02 PM
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Quote:
Originally Posted by xjrwithproblems View Post
Hey Gchin, thanks for the advice. I checked my plugs and grounded them to check for spark, they all have a nice blue spark so i don't think that could be the problem.

Xjrguy, This was actually what i was first suspecting as I did my tensioners not too long ago. Pulled off the valve covers and the cam flats are perfectly aligned.
Well then, I think the next thing to suspect is the throttle body itself. You have the first AJ27 model, and the ECM does not have the correct software to store a host of faults related to the throttle body. Certain cars can be updated to read these codes, but SOME CANNOT, and to try an update on one of those will ruin the ECM. The easiest thing would be to substitute a throttle body from a car that performs OK, but that isn't always handy.

I wish I had a better answer.

Cheers,
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Old 06-28-2011, 02:38 PM
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Hey XJRGuy, to me, it really seems like it has the symptoms of a fuel issue. I just ordered a live data software/port; this should give me a better idea of what is going on.
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Old 06-28-2011, 03:03 PM
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Quote:
Originally Posted by xjrwithproblems View Post
Hey XJRGuy, to me, it really seems like it has the symptoms of a fuel issue. I just ordered a live data software/port; this should give me a better idea of what is going on.
Ok, we'll see where you end up.....

Cheers,
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Old 06-28-2011, 03:34 PM
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Default Battery Disconnect after cleaning Throttle Body -

By xjrguy -

[quote=xjrguy;370180 First, if you cleaned the throttle body, have you disconnected the battery so it can reinitialize the base air. It has to do that since there is now more air getting by the butterfly with the bore cleaned.]

Tried to find on the Forums the sequence for the battery disconnect, no luck. Anyway, is the proper procedure disconnect the negative and wait 30 seconds before reconnecting? Thought I saw somewhere, where the negative lead was actually touched to the positive lead and this inturn
reset the computers.

My problems are pretty much like xjrwithproblems. Today I can not get it to come out of 'fail safe'. I have a P1229 Fault 'Throttle Body' and I think the brushes are getting a little worn. Am going to re-clean again, clean MAF, check the 'pre-loader orfice', check pipes/hoses/tube/elec connections and hopefully all will be well enough until I get a new (rebuilt) throttle body. I have a 2001 XK8 at 97,000 miles, drive everyday and love it...
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Old 06-30-2011, 11:55 AM
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to the OP, have you checked your fuel trims to see if you're running rich or lean? I was running lean on both banks, had the rough idle at start, but it was never enough to trigger a Check engine light. I had multiple air leaks, the worst one coming from the positive crankcase ventilation line returning from the passenger side to the lower elbow on the throttle body. There are lots of places where a little vacuum loss here and there can add up to the point where the ECM cannot keep up appearances of smooth idling. I was in the +8 - + 10% on my long term fuel trims, and short terms were always positive, sometimes jumping to + 15% when the throttle body was opened up.

If you know your running rich over lean, that'll lead you down a totally different path to diagnose.
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Old 07-01-2011, 08:34 PM
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thanks for all the input. my new scanner with live data hadn't come in yet, and all this nice weather really made me want to get the car fixed so i can drive it again. Took it to my very trusted jag/land rover mechanic, and he diagnosed it as a bent driveplate. He read the data, and showed that the spark/fuel/timing was off ( i hope i got that right) and he showed me the driveplate on the lift, and some of the squares were badly mangled. According to him, the CPS is not reading properly due to these mangled squares in the driveplate. He says i need to remove the tranny and put in a new driveplate. Even though he gave me a price break, it is still a lot, and I have removed and replaced tranny's before, so i think i can tackle this myself.

I am assuming that when i did my tensioners (first time ever doing them), i screwed up the squares on the driveplate when i locked it to remove the crank pulley.

Does my mechanics diagnosis seem right? He is very experienced, but i wanted to get a second opinion. Also, according to jtis, it looks like there is a special jaguar engine suspending bar that i need to use to support the engine when removing the transmission. Does this really need to be used? I wasn't planning on fully removing the tranny, just backing it out enough to where i can remove the driveplate with a crescent wrench (8 inches max).
thanks again guys
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Old 07-01-2011, 10:06 PM
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Quote:
Originally Posted by xjrwithproblems View Post
thanks for all the input. my new scanner with live data hadn't come in yet, and all this nice weather really made me want to get the car fixed so i can drive it again. Took it to my very trusted jag/land rover mechanic, and he diagnosed it as a bent driveplate. He read the data, and showed that the spark/fuel/timing was off ( i hope i got that right) and he showed me the driveplate on the lift, and some of the squares were badly mangled. According to him, the CPS is not reading properly due to these mangled squares in the driveplate. He says i need to remove the tranny and put in a new driveplate. Even though he gave me a price break, it is still a lot, and I have removed and replaced tranny's before, so i think i can tackle this myself.

I am assuming that when i did my tensioners (first time ever doing them), i screwed up the squares on the driveplate when i locked it to remove the crank pulley.

Does my mechanics diagnosis seem right? He is very experienced, but i wanted to get a second opinion. Also, according to jtis, it looks like there is a special jaguar engine suspending bar that i need to use to support the engine when removing the transmission. Does this really need to be used? I wasn't planning on fully removing the tranny, just backing it out enough to where i can remove the driveplate with a crescent wrench (8 inches max).
thanks again guys
I think your guy COULD be right on the money! However, I want an explanation of how you think you damaged the driveplate. Did you use the special tool to index the crankshaft/driveplate?? What method did you use to lock it for removing the pulley?? Another logical question is, did this issue begin right after the tensioner repair?? If this sort of damage IS responsible for your rough engine, it would have been immediately evident, and would not come and go.
Sometimes you have to be a detective and see if all the facts fit.

I have used a block of pressure treated wood to wedge under the front of the engine before, in place of the support fixture. That will keep the engine tilted backward so the trans can be lowered and the driveplate accessed. I've done that, but I DON'T recommend it. Especially if this is not done on a vehicle lift.

Good luck!
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Old 07-01-2011, 10:29 PM
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Hey XJRGUY, looking back, i did feel a little turbulence in the cabin but i figured this was from my rumbly exhaust i had put in at the same time i did my tensioners. But it had gotten worse, or maybe i just got more and more used to it. I used the flywheel locking tool to lock the crank and use that position to get my cams lined up, but i read various posts to not use that flywheel locking tool when removing the pulley as it could bend the driveplate (i probably would have been better off leaving it in there) but i used a hefty screwdriver pressed by a jack to hold the flywheel to remove the pulley. At one point the screwdriver slipped while i was removing the pulley bolt, but i didn't think anything of it at the time and just put it back in and continued doing what i was doing.

I just removed the exhaust and the upper tranny bolts, and am now getting ready to remove the driveshaft bolts. My plan, since i am not removing the transmission and just sliding it back a little bit, is to support the engine with a jack and a 2x4 to keep it in it's position. I am going to level my tranny scissor jack under the transmission and gently slide it out until i have enough room to get that driveplate off. WISH ME LUCK!!!
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Old 09-27-2011, 08:04 PM
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I may have done the same thing to the drive plate... did your "slide it back" trick work?
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Old 09-30-2011, 01:50 PM
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Sounds like either a leaking/clogged FI (fuel injector), bad MAF, real dirty air filter or bad plug wire or ???.

Since there is no code, it is most likely a non-monitored part of the engine, get a OHM meter and OHM the injectors, usually if they are bad, they OHM out about 8-11, new are usually 15-18. A leaking injector can look and act fine, it just leaks causing havic with the computer.

Does the car have power up in the 3-5k rpm range.

Use a screwdriver or auto stethoscope and listen for engine noise.

Check the basics first, fuel and air filters, plugs for signs of unusual conditions i.e. wet, oil fouled, etc...

Not sure on XK's, but some MAF sensors can be checked at your local auto parts place, also check wiring for breaks.
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Old 09-30-2011, 04:19 PM
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Looking at Post 1 its idling way too low thats why its running rough,should be idling about 800-900rpm
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Old 10-23-2011, 12:48 AM
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One more thing to consider.....a bad coil or two. My engine was exhibiting the same thing. Rough at idle but smoothed out at higher RPM's. At first the guys in the shop suspected tensioners, but those had been replace quite a while back. It took them some time to figure it out since there weren't any fault codes or check engine lights illuminated. She idles rock-steady now!
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Old 11-09-2013, 03:56 PM
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Quote:
Originally Posted by jimrxk8 View Post
One more thing to consider.....a bad coil or two. My engine was exhibiting the same thing. Rough at idle but smoothed out at higher RPM's. At first the guys in the shop suspected tensioners, but those had been replace quite a while back. It took them some time to figure it out since there weren't any fault codes or check engine lights illuminated. She idles rock-steady now!


How would one go about determining whether the coil is in fact malfunctioning or not? Is there any established value that I could collect and compare with a meter (volt/amp/ohm)? Hate to resurrect threads but somehow I am experiencing similar trouble with very rough idle and smooth acceleration/high RPMs.
Thanks everyone!
Best,
Danny
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