Throttle hesitation

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Throttle hesitation

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Jaguar >> Jaguar Models >> XJ6 & XJ12 >> Throttle hesitation

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Throttle hesitation - 5/23/2008 1:15:02 PM

spiff23542

Posts: 2
Joined: 5/22/2008
Status: offline

I just stumbled across this board yesterday and was impressed with the level of expertise and comraderie that I found. I'm hoping that someone here may have some helpful suggestions to offer with a problem that I've been having but have been too preoccupied to look into. Now that I've finally finished the restoration on my '63 MGB I can place some much needed attention on the Jag. Over the last few years I've noticed that when I step on the throttle from a dead stop frequently there is a sharp drop in engine speed (about 300 - 400 rpm) for a little less than a second before the engine picks up speed again and gets me going. It seems to happen more frequently as the engine is coming up to running temp (first 10 minutes or so). I've asked a mechanic about it previously but either they couldn't replicate it or they had no solution to offer. The car is a 1986 XJ6 and is all original. My first thought would be to inspect the throttle body and clean it out as necessary, but I was wondering if there are any other factors common to these Series III cars that would cause a similar condition. Any thoughts or suggestions would be appreciated.

-Kristian

Post #: 1

RE: Throttle hesitation - 5/25/2008 4:39:18 PM

Jose

Posts: 352
Joined: 3/11/2007
Status: offline

the AFM and AAV come to mind as possible culprits. The AFM specifically, the black electronic box after the air filter canister. There is a fix located at Jag-Lovers which entails soldering a resistor to the AFM's circuit board. I believe this fix came about for the 1986 and 1987 model years.

I am not saying THAT is the problem, but is a potential answer, based on what I have read from others with similar symptoms. You'll need to register there to access the fix, and while you're at it, you can also ask the question at the XJ forum. Not trying to steer you away from here, because I also like this forum, but in issues like this, the answer is already at Jag-Lovers.
http://www.jag-lovers.com

let us know what you found out. BTW, my first car was a 1969 MG-B built in 1968. Brand new!

I still have the Steering Wheel, Owner's Manual, Passport To Service booklet, and Dealer Brochure!

Jose

< Message edited by Jose -- 5/25/2008 4:42:03 PM >

_____________________________

1984 Jaguar XJ-6
1965 Jaguar S type

(in reply to spiff23542)

Post #: 2

RE: Throttle hesitation - 5/27/2008 11:47:38 AM

JagtechOhio

Posts: 473
Joined: 3/12/2008
Status: offline

Greetings Kristian,

Series III cars almost never have throttle body problems. The ignition coils on '86-'87 cars fail more often than the previous models, and can cause this symptom. See if the coil tower is wet, that confirms leakage of the oil inside it. You can use just about any 12v coil to test by substitution...but if you replace the coil, you must obtain the proper coil with the external ballast resistor. Of course there could be many other causes: the Air Flow Meter is one, the Auxilliary Air Valve is not. Aside from inspecting the coil, you should have a look at the cap and rotor.

(in reply to Jose)

Post #: 3

RE: Throttle hesitation - 5/28/2008 2:59:51 PM

spiff23542

Posts: 2
Joined: 5/22/2008
Status: offline

I had the best intentions of getting under the hood this past weekend, but Memorial Weekend festivities seem to have distracted me. Thanks to both Jose and JagtechOhio for their advice. I will likely jump on Jag-Lovers today and see about getting some more information. I registered there a long ime ago so at least that is one step I don't have to worry about. I will also check out that coil as well as taking a peak under the distributor cap. I will let you know what I find. Thanks again!

-Kristian

(in reply to JagtechOhio)

Post #: 4