The oil was dripping from the other FPR which was purchased new a year ago. The one I have on it now is from when I bought the car but it almost brand new as well. I have not had any leaking issues with it yet. Here is a vid I took so you can see the stumbling...if I had been more aggressive with the throttle it would bog down more and backfire.

 

Interesting finding tonite as I was working on the car. I started it and as expected it stumbled, hesitated, and would back fire when throttle was applied briskly. This was after the engine had ran for 2-3 minutes. I continued to let the engine run and I noticed the hotter it got (closer to running temp) the less hesitation issues there were to the point that the car is "almost" cured of the stumbling problem. I am guessing it may be a DME temp sensor issue (which I just replaced last year) or maybe the temp sensor in the AFM? I probably still have the old DME temp sensor and I doubt it is bad so I will reinstall it next time and report back.

 

Why not test them and find out for sure? How to test each is on Clarks, all you need is a multimeter

Also, if you havent already, retrack the pickup arms on the AFM

 

I tested the original DME temp sensor a year ago heating it on a stove and checking the numbers...bought another one anyways because they were dirt cheap. I swapped the original one back in friday but performance is about the same as before with it getting better as the car warmed to full temp but still showing signs of stumbling and hesitation when throttle was aggressively applied. I retracked two different AFMs I had on hand with no performance difference as well. I am to the point that I am probably about to sell the car if I don't get it corrected soon as I haven been working on it for over 3 years now and haven't driven it 50 miles yet. The only thing I have not swapped out yet is the DME/ECU and while it may seem to be the least likely culprit it may be what I purchase next just to finally rule it out.

 

The way I read his post is that the "new" FPR that he put on a year ago was suspected of leaking so he put the old one back on since the "new" one didn't help.

 

I purchased a good/working DME a week ago just to rule it out as I was running out of ideas...performance remains the same unfortunately so I can confirm my other DME is working well and will sell the spare maybe later down the road. I went through the clarks diagnostics again earlier this week and again tonite for the AFM testing and DME temp sensor. The values I am getting on the AFM are good as far as voltage and the linear voltage increase as the AFM opens but not the air temperature sensor reading for the AFM. According to the site "With air temperature between 15 - 30 °C, the ohmmeter should read 1.45 - 3.3 k-ohms." The reading I was getting was .560 and .575 on each AFM I had. I had the multimeter set to ohm's and the finest value it will measure so assuming I am reading it right, my results are basically about a 1/3 of what I should be getting? Could both AFM's now be defective? I measured the DME temp sensor (uro brand and a 1 yr old bosch) and again according to Clark's site "at about 86F you should measure 1.46k ohms" and I was measuring 1.04 and 1.05 for each sensor. This is with the engine cold and at ambient temp of mid 80's. I started the car and got it up to the recommended temp for testing the DME temp sensor resistance when hot and measured .279 where Clarks recommends 280-360 ohms. The car again idles fine once warm and holds a throttle setting without issue but will stumble and sometimes backfire through the intake if you are aggressive with throttle application particularly right off idle or if you are holding the throttle at 3k, let the revs fall and then get back on the gas again.

 

The symptoms are problematic of a lean fuel mixture. If the actual IAT resistance is 1/3 of expected resistance, then the DME would be sensing to lean the fuel mixture, open circuit is lean.
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Suggest retesting both AFM to ensure your contact on the IAT pins with the probes makes good contact.

 

Thank you for the input...I appreciate everyones help so far. I did check the values multiple times with both AFM's back to back and on different days and came up with the same results. The measurements between the two are almost the same. I also checked the values after running the engine for a bit just to see if the values would change radically and there was a change if I recall but it was very small. I can't make sense of it as the car was running good at one point and then it wasn't...I don't know what the failure rate for the AFM's are at this point in their lifespan but it seems odd to have two with the same problem but to be fair, I inherited both of them with the car when I bought it.

 

Just a thought, is the AFM and the Bosch DME compatible? There was a change made by Porsche. Check Clark's Garage for detail specifics

Another thought, if open circuit IAT is lean, then jumper the IAT pins in the AFM which would trick the ECU into a non-lean scenario. I would do it after the engine is at operating temperature.
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I will check the part number on the AFM's but I know the ECU is the "015 early model". The car has run and driven a handful of times without issue so I would be shocked if it was the later AFM and incompatible.

 

I copied this AFM test results from Foolsbry who posted on 944 & 945S Form. The 944 is an '84.

" I did the temperature sensor test on the AFM and it seemed fine, reading at a resistance of around 1550Ohms. Would love to hear some opinions on this!'

He also did the barn door wiper test and results were posted but subject to accuracy on it

 

Bump to get update

 

I had a theory about this, and I'm back to where my car is so I pulled the connector and made some measurements. On mine, the temperature sensor read fine, but I was wondering what the resistance of the airflow potentiometer is. On mine, about 620 ohms. Note that due to the way these are used, the total resistance does not matter much, only that it has the correct curve on the early cars, and is linear on the later cars. 560 or 575 would work fine, as long as the module was trimmed to the correct airflow to voltage output curve.

I suspect you somehow ended up measuring the wrong pins. The temp sensor is connected to the two pins that are furthest from each other.

 

One photo is the IAT resistance reading (inner and outer pins) and the other is with a wire shorting the two wires inside the AFM for the sensor.

 

I ran it till it warmed up and then shorted the IAT but I can't say that there was any noticeable difference as the car still stumbled with heavy and abrupt throttle application.