89 Carrera bucks when warm

[Gil]

My 89 Carrera bucks when warm. It feels like the engine is cutting out or running on less than 6 cylinders. The problem exists only when coasting on a light throttle. There is no hint of a problem when the car is accelerating. Oddly enough the problem also disappears at exactly 2000 rpm. The problem occurs above or below 2000rpm. I have owned the car for 10 years, it now has 96k miles and has been well maintained. I have spent a bunch of money at some great Porsche shops and none have been able to fix.

Any suggestions?

Work done so far:

Replaced: injectors, DME relay, cams reset, valves adj, spark plugs, ignition wires, distributor cap & roter

Tested (parts swapped): Ignition coil, air flow meter, temp sensor, motronic control unit, air box

Other Tests: compression test (160-175), fuel pressure, engine vacuum leak, injection and top end fuel system clean, engine "leak down" test (all cylinders are 2-3%), cylinder head temp, exhaust cylinder temp (1 cylinder runs cooler?), exhaust back pressure, exhaust analyzer indicates lean mix below 2000rpm, heat exchanger, battery, DME pickups, air flow meter, altitude sensor

[jester911]

I have been having similar problems. I have not fixed it yet but I have good reason to believe it is the air flow sensor.
I am getting another one to see if it takes care of the problem.

[Fl Ted]

How was the CHT sensor tested?

[Gil]

I checked my records ...... we actually replaced the cyl head temp sensor with a new one (part # 93060691500).........it didn't solve the problem.

[JeremyD]

I would have said CHT too - pull the plug on the left side of the engine, white one to make sure it's been changed - if it still one plug - it's old.

[Gil]

Hey Jerry, let me know how it goes with the air flow sensor. I am trying to figure out where to make my next "investment" in my car.......while there is still some money left in the kids' college fund.......

[Scuba]

Am I the only one dirty enough to be thinking that if you take this thread title and replace "89" with "Asia" it takes on a whole new meaning (or have I spent too much time at sea)?

[jester911]

Hey Gil, I will post here with the results. My symptoms aren't exactly like yours but close. I think mine is causes by the afm because I took it out and thoughly cleaned it inside with carb cleaner, meanwhile checking all the vacuum hoses.

I put the assembly back together and it worked perfectly for 2 or 3 months. Then it started happening again the last couple of weeks. Not quite as frequent as before but very annoying.

Hey Scuba, it must of been a long cruise man.

[psjoe]

This car is now for sale. The seller mentioned this issue is still present. Any other suggestions for a resolution.
Thanks.

[stlrj]

I have owned the car for 10 years

Did it always do this?

Joe

[psjoe]

I think the issue popped up fairly recently. I pinged Gil the owner/seller he will have confirm.
Thanks

[ruf-porsche]

Originally posted by Scuba
Am I the only one dirty enough to be thinking that if you take this thread title and replace "89" with "Asia" it takes on a whole new meaning (or have I spent too much time at sea)?

Too much time at sea, watching porn.

[stlrj]

All you need to do is find out what was done recently to cause this...make sense?

Joe

[Jeff Alton]

TPS could be bad, it may test fine when cold, but sometimes when they are on their way out they not work properly when they get warm.

Cheers

[stlrj]

My 3.2 had a habit of bucking when I had the mixture set too rich.

Cheers,

Joe

[450knotOffice]

Mine used to buck when it got warm. It would get pretty bad on occasion and would also start with the infamous idle surge. Once it cooled down, all would be fine. I replaced the ICV, removed and cleaned the AFM (including the wiper assembly inside), checked for vacuum leaks, and tried to adjust my idle speed per the manual. No luck.

I finally gave up and brought my car to Hergesheimer and had their guru look at it. He hooked up a gas analyzer, found that my idle mixture was completely off, adjusted it, and then adjusted the idle speed properly. Guess what? The car has never, and I mean never, ever exhibited those symptoms again.

Have someone check the idle mixture while the car is on a Gas Analyzer and then once that's spot-on, make sure the idle is adjusted absolutely perfectly, per the manual. I bet the problem goes away, never to return.

[jabb]

I would also check the O2 Sensor, make sure its OK