Hello all,

2005 S-type 3.0

I'm having a new issue when I'm stepping on the accelerator, it seems to "surge" up and down with speed, kind of a jerking movement gradually slowing and slowing to almost to the point that the car will stop moving (cruising at 1-2mph). I heard a few popping noises coming from the engine compartment when I am going really slow and giving it some gas. It seems to only want to move if i very lightly (almost nothing) push on the accelerator. It also seems to get worse and worse the longer I drive it until i ease up on the gas pedal.
It had doing this the past week, but only on the way home from work when it was hot, cool mornings it seemed fine, but today i almost didn't make it home, so it will stay here until fixed.

I just replaced the fuel filter for a start, didn't help but was dirty anyway, I am going to do a tune up this coming week or so once I order and get some parts such as spark plugs, coils, and valve cover gaskets (small leak), intake manifold gaskets, etc. I will find out what else I should replace while I'm in there. I think I saw a thread on that here somewhere.

I also get the evap leak codes every few hundred miles or so.

I replaced the o-rings at the back of the intake manifold already too a while back. I am at approx 109,000 miles.

Sorry I haven't done much under the bonnet yet to give you some more info, just wondering if anyone had any thoughts or experience on this issue. I couldn't seem to find much yet. feels fuel/ignition related to me.

Thanks, appreciate any thoughts.

 

With air leak(s) you'll have problems. There are threads about where they're likely as well as how to find them plus you have codes as a start...

 

Yeah I get the small and large leak codes its been going on since I bought the car 2.5 years ago, had it smoke tested etc, mechanic couldn't find it.
I have not got any new codes for the new problem. I will look into air leaks. thank you

 

With air leaks being present for what appears to be an extended period of time, I am wondering what shape your catalysts are in at this juncture. Has your MIL/CEL been flashing or blinking on and off at any point during this 2.5 years?

 

Change mechanic to one who has a clue on cars made in about the last 30 years.

+1 your cats may be dead

 

The cats could be breaking up in the exhaust; eventually they can clog it completely.
Had this in a couple of cars.

 

No flashing CEL, or codes to do with that. The exhaust system had been replaced by the previous owner but I'm not sure about the Cats,
Not sure if this makes a difference to cats idea but I went out and started it in the driveway about a half hour later and it Idles smooth and also revs nice and smooth in neutral. got it up to operating temp also...seemed fine.
If my cats were plugged it would not rev nice or idle very well am i correct?
I'll look into it though, I appreciate the ideas. thanks

 

I have not found a jag mechanic around here yet other than the jag delear thats $150 an hour( I guess I need to look a bit harder now), this guy was the mechanic at the place i bought it from unfortunately. I usually do everything myself if I can, but I took it to the Jag Dealer once for some transmission programming once and that's it and I had no evap leak codes at the time it was in there.

 

I don't see why it has to be a jag guy - but it does need to be someone who has a clue about OBD, emissions, etc i.e. has met cars within about the last 30 years and CAN FIX THEM.

 

Just thinking out loud here, but wouldn't you also get a P0420/P0430 catalyst efficiency code at the same time?

On another car, I had a cat break up internally and rattle like crazy for a couple of days. At the same time, the car kept throwing a code for catalyst efficiency, since there wasn't much left inside to do the job.

 

yeah your right. I guess it doesn't have to be. I should have said honest/local mechanic, not jag mechanic.

 

This may be a long process since I started taking the engine apart last night (i'm using a service manual). I got the intake manifold off so far last night. discovered a large mouse nest in the "V" between the cylinder banks under the fuel rail. no idea how long its been there I'll be pulling that out tonight, full of some kind of insulation and miscellaneous crap, and hopefully nothing chewed.

I've also be doing a lot of reading on this and was wondering if a faulty Throttle Position Sensor could be the culprit? It seems like the symptoms are similar with the bucking/jerking, acceleration issues, or would that normally throw a code at you?
Here's the symptoms:

• An unexplainable bucking and jerking in the vehicle
• Sudden idle surges
• Sudden engine stalling without any apparent reason
• Hesitation while accelerating
• Sudden surges in speed while driving on the highway

I'll try cleaning connectors and throttle body (dirty), Mass Air Flow sensor also to see if that helps
What other things should I replace while I have it apart?, I'm at 109k so i'll try to do some other maintenance parts also.
I can take pictures too if anyone would like to see parts, etc.

 

Not a bad thought, but I'm pretty sure you'd get a fault code right away. On 2003+ cars, the position for the accelerator pedal and throttle body each goes through a slick dual-channel sensor. Within each sensor, one channel measures 0-100%, and the other channel inversely measures 100-0%. The cool part is the two channels always add up to 100%, no matter the position. This is an integrity check, so it's almost impossible to get a bad signal through to the computer. If one (or both) channel of the sensor had a dirty spot, the two channels would no longer add up to 100%, and you'd get a code.


As little as possible! Don't change everything in sight "just because". You can easily induce new faults while chasing the existing problem. This is called 'Pulling a Jaimster', as it came to be known in forum folklore.

Fingers crossed you find some easily-repaired damage from the mouse, so at least you know what to repair, versus chasing a ghost.

 

So far it could easily be an air leak (they're common as cars age) - check fuel trims.

 

I will not go 'Pulling a Jaimster' haha. "As little as possible" is probably good advice, I guess it just took me a while to get into it and I'm not all the way there yet, 4 hours to take the intake manifold off due to the excellent pictures in the service manual (maybe too many beers). I figured if there was something prone to failure in there I could do that while I'm at it.
Thanks for the technical TPS info good to know!

 

Will do sir, I guess I'm using this as an excuse to get some maintenance done, I have oil sprayed on my power steering reservoir coming from the LH side valve cover, so I'm taking care of that first. but I will definitely check trims when I get her back together.

 

Ended up being the Fuel Pump which was the last thing I wanted to replace. Ouch! $$$$

 

Glad to hear you got the problem sorted out. For the benefit of the next guy, how did you determine the fuel pump was the root cause? Did the pressure read low on your scanner? IIRC, there's no handy place to connect a mechanical gauge on the 2003+ V6 models.

And thank you, thank you, thank you for posting a follow-up. It gets discouraging to have so many unresolved threads.

 

I took it to a local mechanic, and that's what he told me. I recorded 39 psi using my scanner its I believe its supposed to be 47.9
This was my first time i've opened a fuel tank and I don't know how to test all the components yet or if there is a way to just replace the just "pump" like in the previous models. I was having an issue with the fuel gauge going to 0 and showing a fuel system fault light when I got to a quarter tank I hopefully it will also resolve that

I'm not sure if a cheaper alternative to the OEM would have been just as good and tried it myself, I didn't get enough time to look into that. I needed it back as it's my daily driver.