DougM

Now that I have sorted most of the issues with my car, I am still stuck on one last item. At partial throttle @2000rpm, the car bucks until I let off of it or get on it. The car idles great and runs great above that 2000 threshold. After a short run around the neighborhood to diagnose the problem RPM range, I pulled a couple of plugs and they appeared to be running hot, or so I figure. A short trip never exceeding 3000 rpm and then back into the garage, they were very light brown to white, No wetness at all.
I have read about the recalibrating MAFS and AFPRs. It appears that for some with the same symptoms, the adjustable fuel seemed to be the answer. However, did any of you try recalibrating the MAF first. I figure that when these cars were new, they did not have adjustable fuel so technically they shouldn't be needed now. However, I saw a post that described this scenario happening when new?
My car is not running CATS.
I also adjusted the MAF adjustment clockwise for 6 and 12 turns and that did not appear to change anything. I thought that enriches the mixture. Because the adjustment on the MAF has no stop, what happens if you keep turning it? Just curious.
Just trying to narrow down my fixes before I start throwing money around.

Hilton

You're correct - clockwise on the MAF potentiometer will enrichen the mixture, if the MAF is still able to operate within the correct voltage range.

Given how critical the MAF is to good operation of the car, it would save you a lot of troubleshooting headache on any other issues to have a known-good MAF.

If you don't have a receipt for a new replacement MAF or a rebuild within the last 5 years, I'd be sending it off to someone who can rebuild it, and thus ensure that any running issues are things you can reasonably adjust/fix yourself (your local JDS Porsche agent, Injection Labs etc.).

Typical MAF lifetime varies with mileage, but in my experience 10 years is about the upper limit it seems in which the MAF can still be adjusted to give the manual spec for CO at idle using the potentiometer, for cars with no O2 loop (at least for S4's - all three of mine were factory non-cat cars where you have to set the idle mixture to calibrate for the MAF). With a 10 year old MAF I managed to get the CO up to 0.8% at idle, but it needed the potentiometer set to 750 ohms (above that made no difference on the gas analyser), and the car was noticeably rough to drive with intermittent misfires. A new MAF made a huge difference (and adjusting the potentiometer right back down again).

PorKen

Sounds like the MAF wire is old and thin and reading lean.

You can check what the CO pot is adjusted to at the MAF between pins 6 and 3 or 4, or at the LH connector between 14 and 25. (EZF LH2.2 pinouts) The range is 0-1000 ohms. 380 ohms is the factory 'zero'.

Jadz928

Correct me if I'm wrong, but isn't the MAF pot non-functional on the early Euro LH?

Reads like you're on the right track w/the MAF.

Although, depending on what type of bucking you are referring to...
Light bucking or "lurching" may be noticed at low RPM and low gearing.

DougM

When I say bucking, it is seriously bucking but only at that constant rpm +- a few rpm. If I accelerate normally, it passes through this range without a hiccup. It happens if I stay at this range, which is generally cruising through my neighborhood or in a parking lot. Almost like braking on and off. Not quite whiplash inducing, but definitely jolts you back and forth.
Thanks for the replies. Just trying to get as much info before proceeding.

Jadz928

^^^^
That's exactly how my MAF failed on my '84 Euro.

DougM

First I think I will try a little MAF cleaner. My car had a K&N when I picked it up. Now replaced with stock filter. Maybe at on time it was heavily oiled and has caked onto the hot wire. I did some searching and found that on some MAFs the cleaning helped. I will report back with the results. If nothing, I will send it out for rebuild/recalibrate.

byrdman454

I was in the same position as you when I bought my euro. I said the same things... it should run fine without bucking from the factory. You can probably find these threads if you do a search.

After talking with Dave Roberts and a few other Euro guys on this board, I soon realized these Euros just run lean from the factory. I am not saying that rebuilding the MAF will not solve your problem (temporarily), but it does not take much to get the bucking to come back since the car is on the lean side when running perfect. I would guess that you will end up with an AFPR on the passenger rear and a 85-86 US fuel damper on the driver rear at some point. If you do this and up the fuel pressure, it will mask the rest of the degradation and any other small problems you might have. I fought this bucking problem for a while before I finally gave in a changed the fuel regulators. It transformed the car. I would never change it back now.

smiffypr

Check the part number on the ignition ECU. It should be 928 618 124 00 or 03. If it ends in 02 or 04 that will cause a hesitation around 2000 rpm which will be much worse if the engine is also running lean.
Smiffy

John Speake

The easiest way to diagnose an aged MAF on your non cat car is to measure the tailpipe CO. You should be able to get it near 1% by using the pot on the MAF, turning clockwise to richen. If you can't get to 1% then the MAF needs a rebuild.

My US agent, Louie Ott can test your MAF on his test jig if you don't have access to a CO tester.

I also found on my Euro S2 that ultrasonically cleaning the fuel injectors also removed an intermittant misfire on a couple of cylinders.