Fluctuating engine speed

[yelnats]

Can anyone help with this? I am having problems with my 1999 3.2 sport engine, it starts well enough from cold but leave it ticking over for a few minutes at 700rpm or so and it will suddenly pick up speed to about 1100rpm then after a while slow down again. On the road the racing engine causes all sorts of problems, lots of braking,jerky gear changing, etc. I have fitted a replacement throttle body and maf sensor, new exhaust emissions sensors all to no avail, no one I have talked to including experienced jagmen have come across this problem before, have any of you?

fingers crossed

Yelnats

[joejag308]

I would have suggested the throttle body but if you say its been done it could be quite a few similar related problems.....an E Mail to Dave Marks would be the best option .....

[J44EAG]

I wonder if Rob has seen this problem before?

Take a trawl through this.

http://www.google.co.uk/url?sa=t&rct=j& ... Xw&cad=rja

I think you may need to do some detective work here. I`d be looking for split, cracked or loose rubber hoses. Considering leaking inlet gaskets, possible cracks in the inlet manifold, an EGR valve issue if the car has one or perhaps a dicky air valve unit. The mechanical guard unit and sensor would seem to be an area where I imagine sticking of the mechanism could occur.

Initially I would consider those items and clean out part load breather hoses, cleaning the throttle throat with soft cloth and carb cleaner and generally looking around for anything unusual.

Pages 16, 19, 27-31 and 45 onwards of the above publication would seem to be relevant to the problem you have. The important thing with this type of work is to gain as full an understanding as you can about the induction units and their function. Thereafter, seek and ye shall find may prove to be successful.

Without test gear, it is often not easy to find or test for faults. That is where the material in the publication above becomes useful and will give you more of a fighting chance.

If the throttle body you have fitted is second hand, regrettably it may also have a fault which may be similar to the original unit. Unlikely perhaps, but not impossible.

Sorry to say I have no further experience of the XJ/XK throttle which is different to the S-type fully fly by wire type. Ask me anything you like about that!

Mike

[stuarthardy]

I had similar problems with an Audi and it was lambda sensors.

Mike, isn't EGR for diesels only?

[J44EAG]

It appears not, Stuart.

I`ve heard of them on petrol units before.

Interestingly, I found reference to an EGR valve within the page numbers of the manual in the link above. It says "if fitted" which implies fitment to some of these XJ8 power units. May be these are fitted to models designed for foreign markets?

Mike

[yelnats]

Thanks for your replies gents, interesting. In the meantime I have had a replacement ECU fitted also thermostat and up to now it seems to have cured the problem with engine speed, tickover is steady and even, driving is like it should be. However starting from warm can still be an issue on occasion and something I did not mention before is fuel consumption, I cannot get any better than 20 miles to the gallon.

yelnats

[yelnats]

Well I thought the problem had been fixed but no, its back again as bad as ever engine speed is all over the place , car stationary or travelling. This engine has been looked at by several specialists and plugged into a variety of diagnostic machines, up to now we have had two replacements throttle bodies, two mass airflow sensors, two exhaust gas sensors, one ECU, thermostat and crankshaft sensor fitted, wiring has been checked and air tightness found to be sound. It seems to me everything has been done on a best guess basis and that's all that's on offer at present, just keep fixing new bits on till we find the fault. Hardly!

What to do next, after 18 months on and off with this problem with lots of money spent trying to fix it am I fighting a lost cause? Is there a cure?

Any suggestions would be welcome.

yelnats