89 S4 Idle problem
10-05-2009, 07:47 PM
#16
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Location: Boisbriand, Québec, Canada
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TPS? In Canada, that's a tax! Just kidding...what does it mean?
The car behaves normally under any conditions. I said 500-600 as it reads on the gauge. The Porsche diagnostic computer displays the standard idle rpm figure. I can't recall the numbers but if you say 675, it is 675. It is steady.
I thought about this today, my fuel cap has been modified or broken. The flat inside end of the locking mecanism was missing. It means air could get through the cap lock or fuel escaped through it. I repaired it to make it air tight and I think my idle problem began in the same period. Would there be a possibility that the charcoal canister is clogged, combined with the repaired fuel cap now being air tight, and the fuel tank develloping negative pressure that would prevent the fuel to end up at the injectors with insufficient pressure?
That's a weird scenario! What do you think about that?
The car behaves normally under any conditions. I said 500-600 as it reads on the gauge. The Porsche diagnostic computer displays the standard idle rpm figure. I can't recall the numbers but if you say 675, it is 675. It is steady.
I thought about this today, my fuel cap has been modified or broken. The flat inside end of the locking mecanism was missing. It means air could get through the cap lock or fuel escaped through it. I repaired it to make it air tight and I think my idle problem began in the same period. Would there be a possibility that the charcoal canister is clogged, combined with the repaired fuel cap now being air tight, and the fuel tank develloping negative pressure that would prevent the fuel to end up at the injectors with insufficient pressure?
That's a weird scenario! What do you think about that?
10-05-2009, 08:55 PM
#17
Rennlist Member
TPS is the throttle position switch. Its located under the intake manifold and is easilly tested.
Engine off turn the throttle cam in the rotation of opening the throttle and you should hear a 'click' just off the fully closed position.
The ISV also controls idle and again is located under the intake; it can be 'freed' with a lubricant if its thought to be stuck.
With regard to the fuel cap; drive around with it off and see if you have the same issues..............if not............voila
Engine off turn the throttle cam in the rotation of opening the throttle and you should hear a 'click' just off the fully closed position.
The ISV also controls idle and again is located under the intake; it can be 'freed' with a lubricant if its thought to be stuck.
With regard to the fuel cap; drive around with it off and see if you have the same issues..............if not............voila
10-05-2009, 10:09 PM
#19
Rennlist Member
Confusion Reigns Supreme..........
In that case, ignore earlier comment about idle mixture pot, it is not wired ito the LH on your car.
A vac leak would usually give too high an idle speed.
Does it idle at higher rpm while warming up, as it should, then settle down to a steady 675rpm when at normal temp ?
A vac leak would usually give too high an idle speed.
Does it idle at higher rpm while warming up, as it should, then settle down to a steady 675rpm when at normal temp ?
Mike's old '90 ROW is my problem now...... definitely has cats. So, what John's saying is that the adjustment to the pot could not have adjusted the mix?
Just as a note, I've made considerable headway in getting the emissions down...cam timing was really screwed up (partially my fault when I did the TB/WP, but once we started adjusting the setting, there's no way it was all my doing. and..new rotors, caps and plugs, some vacuum work etc. etc. etc. Still seems to be running pretty lean though based on the plug readings. Intake refresh coming very soon now.
In that case, what did the adjustment do if anything? The car still does the extreme low idle occasionally, only when heat soaked, and when the throttle is blipped, everything goes back to "normal".
Sorry,....Thanks!
10-06-2009, 01:06 AM
#21
Official Bay Area Patriot
Fuse 24 Assassin
Rennlist Member
Fuse 24 Assassin
Rennlist Member
My car just did this and the LH is now sitting in a USPS box.
Just saying.... I would recommend having a connection to do a swap just in case.
Just saying.... I would recommend having a connection to do a swap just in case.