When I am going at a constant slow speed my car seems to ' surge' slightly up and down the revs. As soon as I put my foot down it returns to normal. Any ideas?

Keith
2003 4.2 XKR convertible

 

Could be time for a Throttle Body clean......

Graham

 

Good day!

It could be a few things... Air flow sensor, Oxygen sensor giving the computer false readings which the computer compensates by adding more or less fuel, like Graham said about the throttle body... Is it low speeds or low RPM's... If you keep it in first and wind that out to 3500 RPM's, does it still do it?!

Cheers!!

 

Cleaned T/B recently. Its at low revs, not idling,when moving. It almost feels like the car is searching for the right gear.
[no codes showing]

 

You are right, in a way, it may be looking for a gear. The torque converter on some 4.2's with the ZF 6HP26 tranny of this age has a fault that causes it to lock and unlock on steady driving. At some point a code will be thrown though. If you have no code, it might be something else. The fix is replacement. This shows up more on the XJ8 but this is basically the same converter and tranny.

 

Your scaring me' Oldmots'. When you say replacement, due you mean a new Torque Converter?

 

How do you clean throttle body? The surging is at low RPMS and it helps to be in 4th gear until you reach 65 and more then I shift to 5 if I remember.

 

My knowledge of the trans in limited but I think if you put the trans into sport mode and the surging disappears it is a good indication the torque converter is locking up but I will leave it up to the experts.

As for cleaning the TB this might help JagRepair.com - Jaguar Repair Information Resource

I hope this helps

 

Mine 'surges' in sport mode aswell

 

The symptom of the torque converter problem occurs about 50 mph. If yours is doing this, research the problem, it is on this site under the XJ8 X350 early models (2004). Like I said, it usually results in a code.

 

Mine does the same thing, under the same conditions.
No code for this specifically so far...

 

My 03 XKR does exactly the same thing as I am driving out of the neighborhood at a slow (20-30 mph) speed. After I drive for ten minutes or so it seems to be fine. I suspect it is the throttle body or mass air sensor in need of cleaning, but it is just not bad enough yet for me to do anything about it yet. I`m interested in your experience with this if you decide to clean the TB or MAS. Let us know!

 

Especially useful if you do only one first and then check for results before doing the other. This will give good information on whether it's TB or MAF or both.

Graham

 

I would clean the TB and MAFS and along with that I would add a can of BG 44K to your fuel tank and see what takes place. This is a procedure for cleaning the MAFS

Link: JagRepair.com - Jaguar Repair Information Resource

I hope this helps.

 

My 03 XKR has done this same exact cold surging since I bought her 18 months ago.

My mid-year 03 with the 4.2L engine has the confounded turd of a transmission ZF 6HP26 that, by the way, cannot be held in first gear - because it cannot be manually placed in first. (Apparently, Jaguar & ZF believes we bungling fools cannot be expected to understand the need to shift into 2nd gear at a sensible RPM whilst accelerating briskly.)

I have done all manner of cleaning to the T/B and MAF sensor, changed the fluid and filter pan - using ZF lifeguard fluid, "reset" the transmission using the dealer service department prescribed goofy "do si do" sequence and so-far nothing has made a BIT of difference. She still surge surge surges when cold until full operational temperature is reached - whether in "sport mode" or not. And like other's, no code throwing... So far.

With my car, it's not so much more than annoying - and using "sport" mode to hold her in a lower gear (higher RPM) longer as she's warming up DOES make the surging effect less bothersome.

I have read that many of us experience the same phenomenon. So I have resigned myself to consider the "bother" as just one of our car's "scars in fine leather", proof of the origin and authenticity of their Coventry heritage.

Quite,

 

Thanks for all the info guys. My symptons are the same as 'cpm53' and I have tried the same remidies as 'maxwdg' to no avail. Just a thought , would a blocked fuel filter have these symptons?
Regards
Keith

 

Keith,

You'll find many posts from US members reporting problems with both blocked fuel filters and failed fuel pumps. It's a regular issue.

Strangely this doesn't seem to be such a problem in the UK.

I can't see any other explanation for this than fuel grade and quality. We have 5% Ethanol whereas the US is (I think?) 10%. On the rare occasions I've had fuel tanks off or drained, there's been little or no water or sediment in the bottom. I've also cut fuel filters open from Jaguars with up to 100K miles and found little contamination.

That being said, you could well have a blocked filter!

Graham

 

The problem could be a lot of things from a fuel filter to a fuel regulator and many others. I would take one step at a time and try the cleaning the TB & MAFS and add fuel additive BG 44K you have nothing to lose but time.

 

Keith,

There's plenty of fuel additives available here in the UK. This is the lowest cost UK supplier I can find for the one Gus recommends:

BG 44K - Fuel System and Injector Cleaner | eBay

Many US members have used this specific product with good results.

Graham

 

Jaguar Dealerships in my area are now using it and I have been using it for years.