A bit of background. I'll try to be brief.

Over the years I and a few others have reported a distinct rough running when idling in "P". Shift into "R" or "D" and the idle becomes smooth again.

I know of only one person who went to the effort to fix the problem. In that case, at least, a faulty injector was the problem. Apparently the one injector was lazy and did not operate at a very low pulse width situation....such as "at idle, in Park". I recall there was some difficulty in isolating which injector was the culprit

Just recently the situation has become much worse on my car. The roughness is much worse and will continue at least through 1500-1700 rpm when in "P", accompanied by a pronounced "bump bump bump" misfire sound from the exhaust.

My first thought is that I can't postpone injector replacement any longer.

But here is my question......

We know that the transmission electronics "tell" the ECU when the trans is in "P" or "N". So....what exactly does the ECU do with the "Park/Neutral" signal from the transmission? How/why is that signal used by the ECU?

I'm just wondering if there is something else I should be going after besides the possibility of a faulty injector.

Thanks for any insights.

Cheers
DD

 

Anyone?



Cheers
DD

 

I'll have some guessing Doug.

The "P" and "N" signal as best I can determine, is informing the ECU of a non-load situation, and coming out of those positions informs the ECU of a pending load, and it adjust the idle stepper motor accordingly to prevent stall. Much like when the A/C is turned ON. Also the power steer load, adjusts idle a smidge as you turn the wheel. All these are done by sensors on the item, AND, the pulse the CAS measures on that toothed wheel. Apparently the CAS is accurate to a millisecond.

The fact yours is so prominent at idle and higher revs, and only in a "non-gear" is weird at best. I am not convinced that the trans signal would have that much effect on anything fuel related.

An injector plugging sort of makes sense, but I would have thought that loaded performance would be worse than unloaded. Same thought process for a coil.

What exactly happens in "D" or other "gears" is unsure in my head, but idle speed compensation is a given, and I suppose fuel trim also would be getting adjusted. So if in "P" and "N" it is leaning off too much, a misfire would be a certainty.

Based on that thought an O2 sensor, maybe??.

TPS orientation has got lost, and it is out of sync with the rest of the system, giving a lean burn maybe??.

Not much help maybe, but its all I can think of at the moment.

 

My thought as well






I agree







Weird indeed, but not unheard of. I've ignored it for ages. After all, how much time does a person spend idling in "P"? But the recent worsening has caused me to revisit the issue....as much from curioisty as anything else






I'm not *convinced* either. But.....if there was a no load idle "map" that further reduces injector pulse width, that might be something to think about






I recall from the other fellow's postings (this was several years ago) that it was a problem with plugging but, rather, an electric defect where the injector just wouldn't operate at a very low pulse width command.

However, I wouldn't rule out a plugged injector personally. *IF* I'm correct about a minimal pulse width being commanded in "P" then a partially plugged injector might well be unable to deliver enough fuel. Then, when a drive gear is selected the pulse width is increased enough to overcome the partial clog. I dunno. Just speculating.


I would normally agree but my own experience with coil failures (which can now be described as "noteworthy", perhaps even "vast" [grin] ) is that a failing coil does not always react to increased engine load. I can't explain it.




Which is the direction of my speculation



I'm pickin' up what you're layin' down :-). We just need someone who truly knows to come along and tell us we're right of full of sh*t :-)






On the scan tool (at least) the O2 sensor activity looks good.

Ross talked me into having a dealer re-orient my TPS and O2 sensors but I haven't done so yet. The first and closest dealer wants $200+ to do so (plus another apprx $200 to just pull and clear air bag codes). It's not in my budget for the month as some other repairs have taken priority ( two more new coils for the Jag and a new windshield on the Honda)

Thanks for replying and giving me some things to mull.

Cheers
DD

 

Doug my car had that same problem you know what fixed it getting Andy to remap my ECU smooth as a baby's proverbial spent lots of money originally on lots of things
My Indie even said these cars get a bit rough as they age
(I always thought things got better when aged LOL)

 

I'd love to have andy re-mapmy ECU. Maybe one day in the future.

I do have an update, though. I was able to (mostly) fix the problem with no money spent.
As a result of mulling, tinkering about, and feeling sorry for myself I decided to check the inlet manifold bolts. They were all about a quarter turn loose.

I was excited about finding this but disappointed when the problem remained and perplexed that immediately afterward my STFTs on one bank went crazy. I was half tempted to loosen 'em up again !

However......

I drove the car to work yesterday .....32 miles.....and on arrival noticed that the idle was vastly more smooth and the STFTs were back in the the normal range.

I think there *was* an air leak but it took the ECU a bit of time to realize it was fixed.

Some roughness remains but the outright misfire appears to be totally gone. At this point I'm calling it good and will wait for any further developments.

Cheers
DD

 

SWEET, and a cheap fix is always a bonus.

Fingers crossed the ECU stays happy.