[xj] RPM recovery following accelerator quick press?

Basically, if I depress the accelerator and release, the RPMs increase as
expected, and then enter a momentary (approx. .25-.50sec) “refractory
period,” before returning to idle RPM. Might this have something to do with
AFM adjustment, or idle mixture adjustment ?? This has not been a major
problem, and has not caused any performance degradation as far as I can tell.
I just was curious what this might indicate. My suspicion is that the
mixture is too lean causing a lean condition. Thanks for the tips ??

Thanks to all for the help with the previous fog light post !!

Jon Rhoad
85 XJ6 III (USA)
77 FIAT Spider 1800cc

JON,
I neither a Jag expert nor engineer so consider this entire response to be
in the IMHO category, but I think this anomaly is a “non-problem”. It is
evident on many cars. I believe the theory is that a delay will allow an
extra moment for fuel to burn. Many cars have a throttle control motor to do
this. On our Jags it must be built into the ECU software (this assuming my
theory of the situation has some element of validity). I don’t think idle
mixture has any bearing on this. FWIW my jag does same thing although I
never noticed until you mentioned it, Jon.

Many cars have a pronounced closed throttle fuel cut-off which can create an
annoying surge/bump on closed throttle. I’m not sure how Jag/Bosch handles
closed throttle fuel off. Maybe there’s a Bosch F.I. book out there…

Doug Dwyer----- Original Message -----
From: JONRHOAD@aol.com
To: xj@jag-lovers.org
Sent: Friday, March 03, 2000 11:38 PM
Subject: [xj] RPM recovery following accelerator quick press ?

Basically, if I depress the accelerator and release, the RPMs increase as
expected, and then enter a momentary (approx. .25-.50sec) “refractory
period,” before returning to idle RPM. Might this have something to do
with
AFM adjustment, or idle mixture adjustment ?? This has not been a major
problem, and has not caused any performance degradation as far as I can
tell.
I just was curious what this might indicate. My suspicion is that the
mixture is too lean causing a lean condition. Thanks for the tips ??

Thanks to all for the help with the previous fog light post !!

Jon Rhoad
85 XJ6 III (USA)
77 FIAT Spider 1800cc

Indeed the slow-to-return-to-idle trick is an air-pollution control idea, to
avoid partial combustion. 3 of ours do the same thing, including the Jag.
Our Sprite, however, has no such issue and no pollution controls. High idles
when cold have similar motivation.

Alex
79xj6L SII

DOUGLAS DWYER wrote:>

JON,
I neither a Jag expert nor engineer so consider this entire response to be
in the IMHO category, but I think this anomaly is a “non-problem”. It is
evident on many cars. I believe the theory is that a delay will allow an
extra moment for fuel to burn. Many cars have a throttle control motor to do
this. On our Jags it must be built into the ECU software (this assuming my
theory of the situation has some element of validity). I don’t think idle
mixture has any bearing on this. FWIW my jag does same thing although I
never noticed until you mentioned it, Jon.

Many cars have a pronounced closed throttle fuel cut-off which can create an
annoying surge/bump on closed throttle. I’m not sure how Jag/Bosch handles
closed throttle fuel off. Maybe there’s a Bosch F.I. book out there…

Doug Dwyer

----- Original Message -----
From: JONRHOAD@aol.com
To: xj@jag-lovers.org
Sent: Friday, March 03, 2000 11:38 PM
Subject: [xj] RPM recovery following accelerator quick press ?

Basically, if I depress the accelerator and release, the RPMs increase as
expected, and then enter a momentary (approx. .25-.50sec) “refractory
period,” before returning to idle RPM. Might this have something to do
with
AFM adjustment, or idle mixture adjustment ?? This has not been a major
problem, and has not caused any performance degradation as far as I can
tell.
I just was curious what this might indicate. My suspicion is that the
mixture is too lean causing a lean condition. Thanks for the tips ??

Thanks to all for the help with the previous fog light post !!

Jon Rhoad
85 XJ6 III (USA)
77 FIAT Spider 1800cc