hesitation when accelerating - RESOLVED
 

hi all, still totally in love with the jag and having a small problem.
Often, especially when cold...when accelerating on an on-ramp from 30-50mph, the engine starts hesitating.
It clears up if i give it more gas or if i let off the gas a little.

It feels vacuum leak related possibly. Any idea what might be causing it?

iownme, check the big 3 vacuum points and make sure that they are all good. After that, try running a bottle of fuel injector cleaner through the car and see how she responds after that.

Thermo, i should have mentioned that i had visually checked the main vacuum culprits and felt all around them, i will spray the hoses with carb cleaner while the engine is running to see if the idle changes, i'll get a fuel treatment today and also check the throttle body for build-up.
I just wanted to check to see if there was a common culprit for this issue mainly happening at low rpm's and with a cold engine

I would also say to get a can of MAF sensor cleaner. It can be something as simple as the MAF sensor just needs to be cleaned. A can of that stuff is cheap (less than $5). A single can is probably enough to clean the MAF like 30 times. The only caution I will tell you is to not spray straight down the hole. Put the spray straw in at an angle and let the fluid bounce off the side of the sensor near the wires that are inside. The wires are thin and spraying straight down can possibly damage the wires. But, bouncing the spray will keep everything good.

i sprayed all the vacuum lines while engine was running and no change in idle.
i've noticed pretty poor milage also.
i put a can of slick50 gas treatment in but have not driven it yet. I bought a can of seafoam and will do an induction clean when i get back to NY at the weekend. Can i induce the seafoam through a small hose into the hole where there is a vacuum line just behind the throttle body?, needs to go to all cylinders!.

Do i need to use specifically MAF cleaner or will carb cleaner work?

Tomorrow i'll get to cleaning (if necessary) the butterfly in the throttle body

iownme, as for cleaning the MAF sensor, only use MAF cleaner. I can't say that the carb cleaner would do to the MAF sensor. Same thing with the throttlebody. The throttlebody has a protective coating on it and using the carb cleaner will strip this coating right off. Throttlebody cleaner will not.

As for doing the seafoam, that is the port I used. if you can find one a little further upstream, that would be better now that I think about it.

Thermo....WOW...thanks for letting me know that, i was going to do it shortly but now i'll wait till morning to get throttlebody cleaner and MAF cleaner

There is another port upstream but it appears to me to only go to 3 cylinders?
I never plugged the vacuum lines when unplugging on other cars, do i need to plug the vacuum line when "foaming"

What a funny coincidence, I haven't had a single problem with my jag even though it's at 138k miles...That is until recently my car has also started hesitating during acceleration especially when going up a hill. There is a jerking that can be felt in the car as I accelerate up a hill. I have swapped out spark plugs, cleaned the TB, cleaned the MAF (multiple times), new fuel filter, and I routinely pour in injector cleaner. This has me really perplexed. It did end up throwing a CE light once (p0175- bank 1 too rich). Perhaps it is the cold air intake that I have?

AaCapiz....same symptoms as me!...i'm planning to do all that you have done, so your post makes me nervous :+)
did you change the upper intake gaskets when you changed the spark plugs?
did you spray the vacuum lines with carb cleaner of something similar to check for vacuum leaks?

iownme- I fought this same thing. I tore it down checking everything as I reassembled it, (used same gaskets as they were new) the only new parts were a set of Bocsh plugs and a concentrated mix of injector cleaner (full can w/ 1/8 tank of fuel). Runs fine now. disconnected battery during process so it had to relearn everything. I connected my scan tool and watched it as it warmed up. The o2s (sensors) are a bit slow (135k)but otherwise all looks ok.The STFT is ok but the LTFT still is questionable.(STFT is short term fuel trim and LTFT is long term. I would like to know what all the readings were when it was new. (03 X type 2.5)I might have to go to ALLDATA to see if it gives me some stats.

iownme- yeah I did end up swapping out the upper intake gaskets, but I have not yet checked for vacuum leaks, other than just an audible test. I hope I figure out what it is soon because it is starting to get really annoying going up hills. :( Another weird thing is my car is not idling rough, its just that jerking/hesitating problem.

aCapiz... is your fuel milage bad also?, mine passed my leak test, but i imagine an upper or lower plenum gasket failure could give this symptom also, so no leak test for that!.
Mine also idles fine, such similar symptoms leads me to suspect it's a sensor issue

iownme- yes, my fuel milage has definitely dropped, it's down to about 21 mpg on the highway whereas before I was getting around 28. Since I do have the cold air intake installed, I think i'm going to put the oem airbox back in to see if that makes any difference. Or maybe our MAF's are on their way out???

I checked on ALLDATA and it said in big letters DO NOT CLEAN THROTTLE BODY. and have heard if you remove the coating it's very expensive.

billbjork, I don't want to contradict what you posted as there is some truth to it. But, at the same time, are you going to kill the car if you do, NO. Any vehicle with over say 50K miles on it, this coating is probably worn off already anyways since air is semi abrasive. So, as you run the engine, the air is slowly stripping (think of sandblasting) this coating off. now, it won't come off really quickly, but it will wear away (relate it to the metal wear of your piston rings). So, most of us with a 5 year old car don't really have any coating left. Now, I will admit that I recommend the throttlebody cleaner as you don't want to strip off any coating that may be left though too.

Besides, all this coating is for is to help prevent the build up of deposits inside of the throttlebody. Even if you stripped the coating off 100%, all this truely means is you have to now work in planned maintenance on your car to clean out the throttlebody on a periodic cycle (say ever 10K miles). Else you can have a sticky throttlebody which can lead to other issues (high idle, car not wanting to take off, etc).

So, in short, a lot of people fail conservatively and tell people not to clean the throttlebody at all. But, I have cleaned my numerous times and my car is still running just fine. The trick is knowing what you can and can not do.

Today i replaced the spark plugs and upper intake gaskets. The job went really quick and easy, probably took about an hour start to finish. While i was in there i cleaned the MAF with MAF cleaner and cleaned the throttle body with TB cleaner.
The old plugs were NGK iridiums, i checked the gap as they looked old and the gap was 0.65...waay out!. My replacements were Bosch 2's (2 electrode type)

Put it all back together and the car runs much better now, also the hesitation which i was complaining about has cleared up.

Acapiz..(and others) I think the hesitation may have been caused from the fact that the corrugated pipe from air box to TB was not snugly fitted at the airbox end, I read in another post that was what caused another user to have similar issues. So check the connections at either end of that piece....make sure the band clip is tight also

thottle body
 

Thermo-- You the man- I took ALDATA to literally not remembering they are talking new/ low mileage AND they always don't tell you all scenarios and can't possibly know what individuals will do with the information and what there experience level will be. I know they don't tell you not to spray ice cold cleaner into a hot throttle body either, sometimes common sense, experience and a dash of luck go a long way.I stand corrected.

Major tune up
 

Hello

I own a 06 XJ8 and just started having the same sluggish issue at 140k miles on her. I am not specialist when it comes to auto repair, but if I had a major tune up done shouldn't this rectify the issue?

this car does not like modified intake. I suggest no corrugated tubing and the biggest filter you can fit if its gonna be enclosed like cold air intake - seems sensitive to any restriction. see how large the oe filter is? gotta make sure the airflow exceeds what was going thru there with oe on the new set up. I have 2 conical filters - one is open the other is shielded in a metal cone - my x-type runs poorly with the shielded type

Never mind - I got other issues - need to get her running right before I can tell what intake will work or not - I think I have the intake manifold gasket woes right now - then I can play with air filter choices. On a side note - oe set up has a main air filter and another little filter (breather filter?) behind it... do I need to retain this design when doing an aftermarket set up? Or just do away with it? - will I just need the vacuum tube to have access or access for this breather thingy...