tombtaylor

When I first posted regading my 87 s4 idle problem...I did not mention that when I start it.....without touching the acelerator..the engine revs up to 2K rpm. slowly drops back to 1100 rpm then will drop to 850 or 900, & idles smoothly, then after a few seconds it starts to "hunt" between 850 or 900 & around 1100....then sometimes it will really "hunt between 5-6 hundred & maybe 13-14 hundred...then come back to the 8-11 hundred range...the engine idled fine before I replaced the breather & vacuum hoses connected to the intake & throttle body...I did not replace the small vacuum hoses, only the larger rubber ones...I also replaced the two knock sensors & the pulse sender..
I suppose I'm going to be at the mercy of a good Porsche mechanic as I am not sufficiently talented to trouble shoot it...unless it is totally obvious.
Tom Taylor
1987 Black S4 5 spd

Lizard928

I would start by swapping out the MAF with a known good one.

Mike B

Colin knows his stuff!

I just went through this...similar symptoms but I discounted the MAF as the problem as it was only a year old. It was the MAF. For some reason the rebuilt MAF died. I narrowed it down to the MAF by disconnecting the electrical connection. In my case the car ran better when it was unplugged. I changed the MAF and she runs perfect now.

Good Luck!

tombtaylor

If the MAF is bad would the car run normally, but only affect the idling???
The idle is my only problem....runs fine otherwise..I shall try unplugging it tomorrow tho...
Tom Taylor
87 S4 5spd

no doubt

Wait. Let me guess. You never disconnected your car battery to reset your LH and EZK computers, right?!

Lizard928

The symptom you are describing, tell me that it is the MAF.

It controls the AFR to a fair extent, if it happened when only cold then maybe the tempII sensor. But you do not state that in your OP and I am basing this off all the info I have.

You MAY fix it, or help it with using a can of CNC MAF cleaner as has been previously discussed here.
But regardless try swapping it with another local lister if you have the option (maybe list where you are and put a shout out). This will eliminate it as the problem, or prove it is the problem without forcing you to buy a rebuilt one right away.

I will expand on your symptoms though, the surging idle up and down is almost always caused by a LEAN AFR and the computer catches it as it hits a different point on the fueling chart, and dumps abit of fuel. Off idle you wont notice it as the engine is able to run ALOT leaner without surging. To give you an example, if I tune my car to run anything less than 15:1 AFR at idle, it will surge up and down and try to stall, if I tune it to around 14.4:1 it is much much happier. But on the freeway at 1700 rpm I can run at 18.5:1 AFR without any issues and achieve much better fuel economy because of this. (I wouldnt try this unless you are nuts like me and are willing to risk having to tear your engine out )

tombtaylor

I did unhook the battery.....no change....I am located in shepherdsville, KY, 25 miles south of louisville..so if anyone in the Louisville area has a MAF which I can try...I would be much appreciative
Phone 502 543 7826
Tom Taylor 87 S4

tombtaylor

When I uhooked the MAF connector my engine would not idle at all.....would the temp ll sensor be the culprit...or would a bad MAF allow the engine to idle....
Tom Taylor 87S4

Lizard928

A faulty MAF could still allow the engine to idle. Stick to the origonal plan of trying to find one to swap.

And for the sake of getting attention (and only in this style of case) post a new thread asking for help in your area, with your location in the title, or change the title of this thread to portray it.
This will help to get people from your area click on the thread and contact you.

VehiGAZ

+1. The engine can idle & run on a going-bad MAF. I've heard sooooo many people here and elsewhere say that the engine ran better just by disconnecting the MAF, but mine wouldn't run at all when I was having problems.

(Idle speculation... I wonder if the difference in experience with a disconnected MAF is based on which way it's failing - on the high side vs on the low side.)

VehiGAZ

A bit of an understatement?!

I'd say that the MAF controls the AFR 100%, since it is the MAF's measurement of how much air is entering the intake which determines how much fuel is injected (thus determining the AFR).

If the MAF is measuring intake air wrong, then your AFR is going to be off, too.

no doubt

That test would suggest that your MAF is compensating for another problem. Disconnect your MAF and the other problem is no longer being compensated...going from bad (with MAF) to worse (without MAF).

Lizard928

GAZ,

The MAF does not control the AFR 100%, it also relies on engine temps, air temps, and O2 sensor readings. But it does have the most effect.

No Doubt, it is possible that something else isnt 100% as well. But the MAF is the best place to start.

no doubt

Doesnt' your 87 S4 run without its MAF being connected? Well, his doesn't. So I'd humbly suggest that something is wrong on his car other than his MAF.

Lizard928

Actually I have seen an S4 that would not run without the MAF connected, replaced it and it was perfect. Normally it should run without the MAF connected, but they all have there own quirks, and his symptoms say it is the MAF.