Okay maybe its not all woes

My 1996 XK8 very early car , one of the first batch , wants to rev when I start it even though I dont touch the accelerator pedal ! ! !

Whenever I start the car from cold it revs straight up to about 3500 rpm for about 10 seconds then the revs drop down to normal 800 ish rpm. It cant be doing the engine any good and if anyone is passing by they look at me as if I am mad like I am doing it deliberately

Any ideas what is causing it and how do I stop it ???

Many thanks in advance for any information.

Steve.

 

Assuming no codes/warnings exist...

I would start with cleaning the MAF and installing a new air filter.

Then adjust the throttle cable.

If that doesn't clear it up then clean the throttle body.

If it still is an issue hook up a torque app or similar and look for anomalies.

 

I'd agree with rothwell, I'd start out by cleaning MAF and contacts well, my XKR revs up to about 2500 on startup then drops down to about ~650 after about 3 seconds, I'd also try and hook up a scanner to see where the TPS is at at start up. Shouldn't be high at startup. IMO it's not uncommon for cars to rev high at start up. I'd clean MAF and check TPS and adjust TB cable as need. This can be done by removing the zip tie that holds the square plastic tab in the mount on the TB. IIRC it would go clockwise to remove slack in the throttle cable.

Best of luck

Brandon

 

 

I suggested performing the cable adjustment to ensure that it is functioning correctly.

Assuming the adjustment is done properly, how can you conclude such an adjustment will mask the real problem?

A correctly functioning component should not be able to mask anything since it is doing what it was designed to do.

I like the diagnostic strategy of "if all components are working correctly then their collaboration should work as expected".

 

 

My car has a faster idle when stone cold, then drops down to the correct speed. So there is some sort of cold start cycle, i would start there, maybe a sensor?
I would not touch the cable unless it was touched before this happened. i do not think it is cable length, especially if it was not changed prior to.

 

Thanks for the replies guys I appreciate you taking the time to do it.

Its certainly related to engine temperature. If the engine is even slightly warm it doesnt happen. It starts and runs at 700 rpm straight away warm or hot but if its cold it revs straight up to 3000+ for 6 to 10 seconds then down to 700 to 800.

I have plugged a OBD reader in and cant find any fault codes. The air filter is new and I have cleaned and checked all the sensors etc related to intake and injection system today so I will see how it goes. A mate who is very clued up on cars told me today to switch the ignition on and depress the accelerator full down and release before starting the engine to see if this resets the throttle position on startup ??? Not sure how this works but I will try it. It reminds me of reseting the windows position fully down and up so maybe it works in a similar way ! ! ! I am no mechanic so I wouldnt know

 

It does seem similar to the first start-up after a hard reset, although I don't remember it holding for as long as 10 seconds.

I didn't find much on a search that offered any insight other than what has already been posted above and possible battery issues, except this thread by Dogspaws (sadly left hanging) from the UK forum:

https://www.jaguarforum.com/showthre...l=1#post784680

Post #10 offers a view on why it might only manifest on a cold start.

You mention the window reset procedure - it's not something you're having to do regularly, I guess?

 

Ouch! 3000 is a lot. The rest sounds OK.

I don't know what would cause 3000+ yet be OK afterwards but it sounds well out of spec. (1000+ would be OK.)

 

I don't know if this applies to the very first cars, but have a look at this. Obviously 3500 rpm is way too fast, but it is supposed to idle fast on startup, then drop. Perhaps a new battery is needed if the car is "forgetting" some value:-

Jaguar AJ-V8 engines idle at higher speeds during the warm-up period than earlier AJ16 and V12 engines. This may cause unjustified concerns from customers having experience with earlier Jaguar models. Compliance with increasingly stringent emissions legislation requires an engine management strategy employing leaner air/fuel ratios than previously, requiring higher idling speeds. This may be particularly noticeable to the customer on a cold or partly warmed up engine. Once the coolant temperature approaches operating temperature, normal idle speed will resume.

There is a chart here:-

http://www.jagrepair.com/images/TSB/...le%20Speed.pdf

 

I assume you know its supposed to do that? I am sure you do but just checking.

As for cleaning the MAF sensor this may help. https://www.jaguarforum.com/showthre...l=1#post940292

 

This cold start behavior is normal, but if it needs modification, take it to the dealer and get the ECU flashed to change the settings. All this programming comes from there. You may be developing an ECU issue, so a spot check is not a bad idea.

 

Sorry but it's not normal to go to 3000 revs, is it?